Class 
 
 Book li'<o 
 
 Copyright ]^^._ 
 
 CX)F»R!GRT DEPOSIT. 
 
PASTEURIZATION OF MILK 
 
 FROM THE PRACTICAL VIEWPOINT 
 
 A HANDBOOK RELATING TO THE INSTAL- 
 LATION, OPERATION AND CONTROL OF 
 PASTEURIZING PLANTS. USEFUL TO 
 MILK DEALERS, STUDENTS IN DAIRY 
 SCHOOLS, PUBLIC OFFICIALS HAV- 
 ING CONTROL OF MILK HAND- 
 LING, AND OF INTEREST TO 
 THE GENERAL PUBLIC 
 
 BY 
 
 CHAS. H. KILBOURNE 
 
 LATE CHIEF OF THE DIVISION OF PASTEURIZING PLANTS 
 NEW YORK CITY DEPARTMENT OF HEALTH 
 
 NEW YORK 
 
 JOHN WILEY & SONS, Inc. 
 London: CHAPMAN & HALL, Limited 
 
 1916 
 
5 
 
 
 Copyright, 1916 
 Bt Chas. H. Kilboubnb 
 
 4i^ 
 
 SEP 28 1916 
 
 C!.A438t)20 
 
INTRODUCTION 
 
 In presenting this book on the pasteurization 
 of milk, the author has endeavored to so handle 
 the subject that the milk dealers, the students in 
 dairy schools, and health department officials who 
 are charged M'ith the supervision and control of 
 the milk sold in their communities, will find in the 
 book practical assistance in their work. Except 
 for the excellent bulletins issued by the United 
 States Government, there are few books which deal 
 with the practical aspects of milk pasteurization, 
 and the author felt that a real need existed for 
 such a work. 
 
 It is possible that his long association with the 
 milk work^ as it has been carried on by the New 
 York City Department of Health, has somewhat 
 colored his views with official conservatism. He 
 has tried, however, to be fair and impartial, and to 
 look at matters from the dealers' point of view. 
 He has presented freely practical lessons which 
 
 iii 
 
INTRODUCTION 
 
 he has learned during a somewhat wide experience 
 in investigating pasteurizing plants. 
 
 If any dealers with questionable motives look in 
 this book for practical suggestions by which they 
 may be able to save milk and cream which is going 
 bad, or if they wish to learn how departmental 
 regulations can be evaded, they will be disap- 
 pointed. 
 
 It is hoped, however, that dealers who honestly 
 desire to handle milk so that it will be safe and 
 salable will find assistance in this book. 
 
 The author wishes to acknowledge the assistance 
 and good advice which he has received from Dr. 
 Wm. H. Park, Dr. Chas. F. Boldune, Ole Salthe 
 and James E. Thomson, and from Inspectors 
 Ryan, Lee and others in the New York City De- 
 partment of Health. Also he wishes to thank the 
 various manufacturers of dairy machinery for in- 
 formation given and illustrations supplied. 
 
 C. H. K. 
 
 New York, September 1, 191 6. 
 
 iv 
 
The Pasteurization of Milk from the 
 Practical Viewpoint 
 
 CHAPTER I 
 
 PASTEURIZATION IN GENERAL 
 
 The guarding of food supplies in large towns 
 and cities is one of the most important functions of 
 government activity. This activity, like all forms 
 of organized effort, has been a gradual develop- 
 ment. In the most primitive communities, individ- 
 uals naturally felt a certain care over the food 
 which they ate. This interest was instinctive and 
 fundamental, since each individual was conscious 
 that some foods were dangerous. He therefore 
 obeyed the law of self-preservation when he se- 
 lected his food. 
 
 As the homes of individuals became more con- 
 gested on account of the increase in population, 
 it grew to be increasingly difficult for the indi- 
 vidual to select the food which he ate. He there- 
 fore came to depend more and more upon the 
 judgment of other people who had either used 
 similar food before or else knew how it was pro- 
 
 1 
 
THE PASTEURIZATION OF MILK 
 
 duced. The substitution of the judgment of oth- 
 ers for his own personal inspection of food nat- 
 urally developed into a certain sort of communal 
 or public control of foods. As communities be- 
 came more and more congested^ it became neces- 
 sary to centralize the control of foods under some 
 definite organization. This centralized control, 
 which was usually at first vested in some private 
 organization, was later taken over by the govern- 
 ment which obtained in the town or city. Thus we 
 have the Boards of Food Control, which are now 
 usually centered in the Health Departments. 
 
 As the inter-dependence of the various towns and 
 cities became more fully recognized, it became evi- 
 dent that not only the cities but the states should 
 on broad lines, regulate the production and sale of 
 foods. This state regulation of foods has been cen- 
 tered partially in State Health Departments, partly 
 in the Agricultural Departments and sometimes in 
 special departments whose duties have been to 
 control the foods sold in the state. These state 
 departments are becoming increasingly efficient as 
 the good work which they do is becoming more and 
 more recognized. 
 
 Since the means of communication and transpor- 
 
 2 
 
FROM THE PRACTICAL VIEWPOINT 
 
 tation are becoming more rapid, the effect is that 
 the world is becoming smaller, and so the consump- 
 tion of foods is not confined to the states where it 
 is produced. The increasing use of cold storage 
 facilities for preserving foods also adds to the wide 
 area from which cities and towns can obtain the 
 foods which are there consumed. It, therefore, 
 becomes evident that state regulation is too narrow. 
 In order to properly protect the citizens, therefore, 
 the general government has taken up, to a large 
 extent, the control of foods which enter into inter- 
 state commerce, and government standards are 
 adopted. 
 
 Among the articles of food which have perhaps 
 received the largest share of attention we find milk. 
 This attention has been deserved on account of the 
 almost universal use of milk, and also on account 
 of the fact that it becomes easily infected with 
 dangerous bacteria, and having become infected it 
 is itself an ideally good medium for their growth. 
 The milk thus becomes so changed or decomposed 
 that it is frequently unsafe for food. The oppor- 
 tunities for infection are many, on account of the 
 many persons through whose hands it passes be- 
 fore it reaches the city consumer, and where it is 
 
THE PASTEURIZATION OF MILK 
 
 perhaps fed to the children who depend upon milk 
 for their life. At any point along the line of 
 travel from the cow to the consumer it may be- 
 come dangerously infected. If the cows from 
 which it is drawn are not healthy, the milk may 
 start on its journey in an unsafe condition. Even 
 if it is perfectly wholesome when drawn from the 
 cows, it may at any point along its line of travel 
 become changed from its natural state. 
 
 Disease-producing bacteria or other less harm- 
 ful germs may enter the milk from stable dust or 
 from the manure and urine which drops from the 
 cow herself. The milk bottles and cans may have 
 been carelessly washed or the water with which 
 the washing is done may be from contaminated 
 sources. Diseased, or unclean persons may be em- 
 ployed in milking the cows, or in handling the 
 milk after it is drawn. Cans or bottles in which 
 the milk is placed may have been returned from 
 the consumer in filthy condition and have been 
 again used for containing fresh milk before being 
 thoroughly washed and sterilized. Contagious dis- 
 ease may have been in the homes from which they 
 are returned. 
 
 Much of the milk in large cities is handled at 
 
 4 
 
FROM THE PRACTICAL VIEWPOINT 
 
 creameries or shipping stations which arc located 
 in the country and from which the milk is shipped 
 to the cities. Thus, there is an added opportu- 
 nity for milk infection on account of the insani- 
 tary buildings or from coming in contact with 
 dust-laden air or diseased employees. Once hav- 
 ing gained access to the milk the growth and mul- 
 tiplication of the germs is aided by the powerful 
 agencies of age and heat. If germs which pro- 
 duce disease get into the milk the danger that epi- 
 demics of disease will occur is a serious one. Each 
 point in the handling of milk is therefore an im- 
 portant point, for the chain of milk safety is only 
 as strong as its weakest link. 
 
 Aside from the danger of bacterial contamina- 
 tion there is of course the possibility of actual 
 adulteration being practised within the legal defini- 
 tion of that term. Foreign substances may be 
 added, such as water, coloring matter, preserva- 
 tives, etc., or the cream may be removed. Such 
 adulteration may be accidental or it may be de- 
 liberately practised, with "malice aforethought," 
 with intent to deceive and defraud the final con- 
 sumer, for the purpose of increasing the profits. 
 On account of the sharp competition which ex- 
 
 5 
 
THE PASTEURIZATION OF MILK 
 
 ists in modern trade, some dealers consider that 
 tliey are justified in doing some things which are 
 objected to by public boards of control. Some- 
 times milkmen will endeavor to save a perishable 
 product by the use of preservatives. This form of 
 adulteration, however, is at present very little 
 practised. 
 
 The importance which attaches to the public or 
 communal control of milk is not the only force 
 which is lifting to a higher level the character of 
 the milk sold to the public. Milk dealers them- 
 selves are realizing more and more that modern 
 conditions are such that only the best and the 
 most efficiently produced and handled product can 
 remain in the market. They are therefore be- 
 coming more and more active in establishing 
 means for effectively controlling their own sup- 
 plies. The methods employed are various. Asso- 
 ciations of men have been formed, the object of 
 which is to secure mutually useful advice and to 
 give each other the benefits of individual expe- 
 riences. 
 
 The larger dealers establish within their own 
 organizations an efficient inspection service and 
 seek by means of laboratory tests and research 
 
 6 
 
FROM THE PRACTICAL VIEWPOINT 
 
 work to study their problems and so secure the 
 best milk possible at the least expense, and with 
 the least amount of waste. Thus the governmen- 
 tal forces and the dealers themselves both work 
 toward the goal of a better milk supply. 
 
 The great importance of the problems which 
 affect the securing of a safe milk supply has led 
 to the publication of many books, in which the va- 
 rious phases of the matter have been considered. 
 The composition of the milk, its chemical charac- 
 teristics, the number and kind of bacteria con- 
 tained, the forms of adulteration which occur and 
 the methods for detecting such adulteration have 
 all been broadly covered. The relation of milk to 
 the public health and the disease epidemics which 
 have been due to infected milk have received large 
 attention in published works. Much has also been 
 published regarding the most effective methods to 
 be employed in the public control of milk supply. 
 
 While there is an extensive literature concern- 
 ing the problems of milk pasteurization dealing 
 with the matter from the theoretical side, and also 
 covering certain special phases of the work, it is 
 rather surprising to find how little of this is 
 available for the practical use of the milkman who 
 
 7 
 
THE PASTEURIZATION OF MILK 
 
 wishes to install pasteurizing apparatus and to so 
 handle his output that the most efficient service 
 can be secured with the least possible expense. 
 This dearth of literature has been no doubt largely 
 due to the fact that the information which the 
 many practical men have gained in their experi- 
 ments has never been so brought together that it is 
 available for the use of those who are seeking 
 knowledge along practical lines. That this should 
 be so is but natural, for several reasons. 
 
 First: The manufacturers who are interested in 
 emphasizing the good points of their apparatus 
 are not inclined to call attention to their defects. 
 
 Second: Milk dealers who, through experiments 
 in trying out various forms of apparatus have 
 learned what appears to be best suited to their 
 needs, are not inclined to publish to the world 
 information which has cost them much time and 
 money to secure. Should they do so, they would 
 be benefitting their competitors. 
 
 Third: Public officials in city, state or national 
 public service, who have made many inspections, 
 conducted tests and carried on extensive research 
 work are comparatively few. In fact, in very few 
 cities is the field for observation sufficiently exten- 
 
 8 
 
FROM THE PRACTICAL VIEWPOINT 
 
 sive to enable such officials to draw unbiased or 
 broad conclusions. State officials are as yet doing 
 little work along these lines. The general govern- 
 ment has been and is now carrying on extensive 
 and valuable experimental work^ and as a result 
 much useful and valuable information has been 
 published.* 
 
 The writer has published some matter which his 
 experience has taught him.f Dr. Rosenau lias 
 devoted considerable space to the subject of milk 
 pasteurization and has given much valuable infor- 
 mation on the subject.]; 
 
 Additional information which is of considerable 
 value has been acquired by the experience of the 
 writer and other inspectors in the New York City 
 Department of Health, working in conjunction 
 with the laboratories. It seems to be proper that 
 this information could be available to the general 
 public. 
 
 As before stated, the application of heat to per- 
 ishable foods in order to preserve them from de- 
 
 *Ayers and Johnson, Bureau of Animal Industry — Circular 
 184 and other pubHcations. 
 
 fN.Y.C. Department of Health Reprint Series Nos. 1 and 27. 
 JThe Milk Question by M. J. Rosenau. 
 
 9 
 
THE PASTEURIZATION OF MILK 
 
 cay has probably been practised since the discov- 
 ery of fire. The earliest record of the application 
 of heat to food in a scientific way was in 1872, 
 when Sheele, the well-known Swedish chemist, 
 discovered that vinegar could be preserved against 
 spoiling by heating it. Soon after this other peo- 
 ple began to preserve fruits, vegetables, milk, etc., 
 by heating them in closed vessels. No scientific ex- 
 planation, however, of the reason why the heating 
 process preserves these foods appeared until I860 
 to 1870, when Pasteur, in his studies as to the 
 causes for the deterioration which took place in 
 wines and beers, discovered that there was certain 
 forms of life previously unknown whose unchecked 
 growth gave to liquor its bad flavors, etc. These 
 were termed by Pasteur "diseases." He discovered 
 that by heating beer and wine to a temperature of 
 158° to 176° F., and holding the fluids at these 
 temperatures for a period of time, the "disease 
 germs," as he called them, were destroyed and the 
 flavor of the liquor was improved, the loss by 
 spoiling being at the same time prevented. 
 
 This discovery was of immense financial benefit 
 to Europe, and in consequence the heating of wines 
 and beers became very generally practised, the 
 
 10 
 
FROM THE PRACTICAL VIEWPOINT 
 
 process being termed "pasteurization," from the 
 name of the man who originated it. At the present 
 time, no brewery is considered to be well equipped 
 and up to date unless extensive apparatus is em- 
 ployed to heat the product before it is placed upon 
 the market. 
 
 The thought that the same principle might be 
 applied to the preservation of milk on an exten- 
 sive scale had its birth in Europe, and it is claimed 
 that the first commercial milk pasteurizer was 
 made by Ahlborn in Hildeshein, Germany, in 1880, 
 and that a similar apparatus was made in the same 
 year by Fresca in Berlin, Germany. The process 
 was later adopted in Denmark, where dairying has 
 reached such a high degree of perfection. 
 
 At all events, the machine now known as the 
 Danish pasteurizer was introduced into this coun- 
 try by Reid about 1895, and is now sold under 
 various names by different manufacturers. Modi- 
 fications and developments of the original idea 
 form the basis of nearly all the pasteurizing ma- 
 chines used at the present time. 
 
 This form is illustrated in Figs. 1 and 2, and is 
 described more in detail later in this book. 
 
 In Denmark the object sought by the use of the 
 
 11 
 
THE PASTEURIZATION OF MILK 
 
 pasteurizer was the improvement of the flavor and 
 quality of butter, the manufacture of which is such 
 an important industry in that country. The pas- 
 teurization of the cream used for butter is there 
 generally practised, and it is subsequently ripened 
 by the introduction of a pure culture grown in the 
 laboratories in order to secure the most desirable 
 texture and flavor. These methods have resulted 
 in the production of a butter in Denmark which is 
 considered to be a standard article. The indus- 
 try has grown remarkably and its products are 
 shipped to England and other parts of Europe in 
 normal times, and have also, in times of shortage, 
 been shipped to the United States. 
 
 When it became appreciated in Denmark that 
 the spread of bovine tuberculosis was a danger- 
 ous menace to the dairy industry, a law was passed 
 requiring that milk whey, etc., which was fed to 
 calves, swine and other animals must be heated 
 before being fed in order to prevent the spread of 
 this disease among the growing stock. This 
 proved so useful in accomplishing its object, that 
 similar laws have been passed in various states in 
 this country. Vermont and Pennsylvania have 
 such laws in the East. Strange to say, many of 
 
 12 
 
FROM THE PRACTICAL VIEWPOINT 
 
 the dairymen object to this^ much preferring the 
 unheated skim milk. The dangers are not gen- 
 erally appreciated. 
 
 It became apparent to some people that that 
 which was good for preventing disease among cat- 
 tle would also be useful in preserving health 
 among children, and in 1 866 Soxhlet advocated that 
 milk which was fed to infants be heated. About 
 this time, Jacobi, the distinguished American pedi- 
 atrist, advised the boiling of milk fed to infants. 
 In 1869 he referred to the apparatus devised by 
 Soxhlet, this being the first American reference 
 to the subject. This was before it was so well 
 known, as is now generally accepted, that milk is 
 a means of carrying infectious diseases, such as 
 diphtheria, typhoid, scarlet fever, etc. Jacobi found 
 that children fed upon boiled milk were less liable 
 to have intestinal disorders, and his long and con- 
 tinued success in treating children tends to dis- 
 credit the assertions made by some that the pas- 
 teurization of milk at comparatively low tempera- 
 tures destroys its nutritive value and is injurious 
 to children. Jacobi still advocates the boiling of 
 milk. 
 
 It was soon brought to the attention of milk 
 
 IS 
 
THE PASTEURIZATION OF MILK 
 
 dealers that milk which was old and liable to be- 
 come a commercial loss on accomit of souring 
 could be saved if it were heated, and that the fer- 
 mentation due to the growth of the enormous num- 
 ber of bacteria in milk could thus be checked. 
 Milk which had been handled in an unclean man- 
 ner, or which had been badly cooled by insuffi- 
 cient icing, or which it became necessary to hold 
 for a long time before sale, could still be made 
 marketable by rapidly heating and cooling it. Lit- 
 tle attention, however, was paid to the matter of a 
 uniform heating of the milk, or to the exact degree 
 of temperature to which it was subjected. Almost 
 no attention was directed to the destruction of 
 pathogenic bacteria. These, in fact, were little un- 
 derstood by the milk dealers, and few dealers main- 
 tained laboratories for studying milk problems. 
 
 On account of the questionable motives which 
 actuated dealers in adopting this method of milk 
 treatment, as well as the faulty methods employed, 
 health authorities, as a rule, at first looked upon 
 the pasteurization of milk with disfavor. It was 
 considered that the process was a makeshift and 
 simply used as a means of covering up bad prac- 
 tices in the production and handling of milk. In- 
 
 14 
 
FROM THE PRACTICAL VIEWPOINT 
 
 stead of encouraging the pasturization of milk, or 
 even ignoring it, health authorities rather took 
 steps to discourage its practice. The desire to se- 
 cure a safe milk supply for the public took form 
 in strenuous efforts to clean up the sources from 
 which the milk was secured, to secure proper re- 
 frigeration and to assure clean handling. The cry 
 was for clean milk as produced from the dairies, 
 and the process of pasteurization was frowned 
 upon. 
 
 In New York and other cities, commendable 
 progress was made in the effort to secure a clean, 
 safe raw milk, and the improvement made in the 
 conditions under which milk is handled, particu- 
 larly in receiving stations and creameries, can 
 hardly be appreciated by those who were unfa- 
 miliar with conditions before the campaign for 
 clean milk was inaugurated. Dairy conditions 
 have also been greatly improved, and the dairymen 
 themselves repeatedly say that they would not for 
 any consideration go back to old conditions. All 
 efforts made to advance the production of clean 
 milk should be continued with unabated vigor. 
 
 It soon became apparent, however, that the se- 
 curing for a large city of a raw milk supply 
 
 15 
 
THE PASTEURIZATION OF MILK 
 
 which could be guaranteed to be reasonably clean 
 and safe was practically impossible. If it was se- 
 cured, it would involve the expenditure of an enor- 
 mous amount of money and energy, which the tax- 
 payers would not approve, and it was seen that it 
 might result in so much added expense to pro- 
 ducers and dealers that the price of milk to the 
 consumer would be greatly increased, perhaps to 
 such an extent that the sale of this valuable uni- 
 versal food would be seriously curtailed. 
 
 Public health administrators were at length led 
 to the conclusion that the pasteurization of milk 
 was the only practical means of securing a sup- 
 ply which would be reasonably safeguarded against 
 dangerous infection. By many persons it was con- 
 sidered to be a makeshift, and it is still so re- 
 garded by some authorities, it being held by them 
 that its employment should only be continued until 
 a clean, safe raw supply can be secured. Others, 
 and by far the majority of authorities, are, how- 
 ever, convinced that pasteurization will always be 
 a necessity, and that even the best of raw milk 
 should be provided with the additional safeguard 
 which will be secured by pasteurization. 
 
 It is even urged by some that certified milk, 
 
 16 
 
FROM THE PRACTICAL VIEWPOINT 
 
 which is the safest raw milk possible to be ob- 
 tained, should be pasteurized before being used for 
 infant feeding. This thought has been strength- 
 ened by information of comparatively recent dis- 
 covery, that milk may become infected through 
 coming in contact with persons who harbor dis- 
 ease germs, but who are not in any way ill. These 
 persons are therefore perfectly innocent of any 
 knowledge that they are a source of infection to 
 milk, and thus a dangerous and insidious menace 
 to the milk consumer. It has been found that cer- 
 tain persons may be, and not infrequently are, in- 
 fected with typhoid bacilli, without they themselves 
 knowing that they are thus infected. Such per- 
 sons are known as typhoid carriers. Other persons 
 harbor the germs of diphtheria in mouth and 
 throat, without having any symptoms of the dis- 
 ease whatever. Such persons may handle milk and 
 unwittingly infect it. 
 
 Within the last few years there have been in 
 different cities epidemics of septic sore throat. 
 These have occurred in Boston, Baltimore, Chi- 
 cago, etc. In Boston in 1911 several thousand 
 persons were made ill by milk coming from a 
 farm where the milk was exceptionally well cared 
 
 17 
 
THE PASTEURIZATION OF MILK 
 
 for.* Many of the persons thus affected died. 
 In 1912 a similar epidemic occurred in Baltimore, 
 where many persons were made sick and many 
 deaths occurred. This was traced to milk infec- 
 tion, f Had these milks been properly pasteur- 
 ized, these epidemics of disease would probably 
 have been avoided. 
 
 Aside from the foregoing considerations, the 
 fact that a very considerable percentage of cows 
 producing milk are tuberculous gives an added 
 reason why it is desirable to heat the milk be- 
 fore use. There has been much misapprehension 
 in the public mind regarding the actual danger 
 which threatens human beings from this source. 
 There seems to be no doubt that these dangers, 
 while real, have been somewhat exaggerated. In 
 the first place, the fact that a cow may be seri- 
 ously affected with tuberculosis does not make it 
 certain that her milk is dangerous to use. If 
 proper care is exercised while the milk is being 
 drawn from the cow, none of the germs will get 
 
 *Winslow, C. E. A., Journal of Infectious Diseases, Volume X 
 
 No. 1, January, 1912. 
 
 tPublic Health Reports, November 22, 1912. 
 
 18 
 
FROM THE PRACTICAL VIEWPOINT 
 
 into the milk. Of course, if the disease existed in the 
 udder of the cow, or in the milk ducts, there would 
 then be direct contamination of the milk as it was 
 drawn. Cows more frequently, however, have the 
 disease in the lungs or other parts of the body, in 
 which case the germs will pass through the alimen- 
 tary tract and be voided with the urine and faeces. 
 If the cows are allowed to become badly soiled, 
 particles of manure and dirt, carrying with them 
 the tubercle bacilli, will inevitably fall into the 
 milk, thus infecting it. It is also possible that 
 dried manure in stables where tubercular cattle 
 are kept will produce dust, which, when stirred 
 up by the movements of the cattle or by persons 
 and by sweeping, may fall into the milk. This 
 danger is probably more imaginary than real, 
 since recent experiments by the Geneva Experi- 
 ment Station * indicate that stable dust plays a 
 part in milk infection which is of comparatively 
 little importance. It is also true that the exposure 
 of manure to light and air for a length of time 
 sufficient to produce a dry dust would tend to de- 
 stroy the tubercle bacilli. The amount of infec- 
 
 *Bul. 409. N. Y. Ag. Exp. Sta. 
 
 19 
 
THE PASTEURIZATION OF MILK 
 
 tion would be therefore comparatively small. It 
 is also a known fact that while tubercle bacilli will 
 live in milk, they will not multiply. 
 
 The apprehension experienced by many persons 
 that they may be infected with tuberculosis from 
 the milk which they consume should be lessened 
 by their knowledge of this further fact, namely, 
 that tuberculosis of the bovine type with which 
 cattle are affected is rarely infectious to human 
 beings who are over fifteen years of age, and 
 rarely causes fatal tuberculosis in children over 
 five years old. The careful examination of hun- 
 dreds of cases where death has occurred from 
 tuberculosis among children appears to conclu- 
 sively show that the danger of infection from bo- 
 vine tuberculosis is largely limited to persons 
 under fifteen years of age. Of deaths from tuber- 
 culous affections of persons under this age, only 
 10 per cent, had tuberculosis of the bovine type. 
 This has been determined for New York City by 
 investigations carried on by Park and his col- 
 leagues, extending over several years, and the same 
 conclusions have been reached by European sci- 
 entists. 
 
 The records of New York City for the years 
 
 20 
 
FROM THE PRACTICAL VIEWPOINT 
 
 1913-1914-1915 show the following interesting 
 facts : 
 
 Deaths of Children Under Fifteen Years. 
 
 1913 1914 1915 
 
 From all causes... 23,574 22,312 23,031 
 From all tubercular 
 
 diseases 1,288 1,166 1,200 
 
 10 per cent of these 
 latter figures in- 
 dicate 128.8 116.6 120. 
 
 These represent the number of persons who died 
 in these years from tuberculosis which was prob- 
 ably of bovine type. 
 
 This means that out of every 1,000 deaths from 
 all causes of children under fifteen years of age, 
 5.4 in 1913, 4.8 in 1914, and 5.2 in 1915, had 
 tuberculosis which was probably of the bovine 
 type. 
 
 While it is possible that bovine tuberculosis may 
 reach human beings through infected meat or by 
 direct infection from dust, dirt, etc., it is probable 
 that most of it is due to infected milk. 
 
 There are many cases of tuberculosis existing 
 
 21 
 
THE PASTEURIZATION OF MILK 
 
 in bones and glands which do not result fatally. 
 Nearly one-half of these are thought to be of the 
 bovine type, and very likely have their origin in 
 milk. 
 
 It is evident, therefore, that while the danger of 
 tubercular infection from milk when expressed in 
 terms of percentages is comparatively slight, there 
 appears to be, nevertheless, a definite danger to 
 children from this source, and the safeguarding of 
 this milk by pasteurization is extremely desirable. 
 
 Rosenau * places tuberculosis first among the 
 diseases carried by milk, thus considering it a 
 greater menace than typhoid fever. 
 
 All these facts have induced most health authori- 
 ties to change their attitude toward the pasteuriz- 
 ing of milk for general use, and it is now the ex- 
 ception instead of the rule to find persons familiar 
 with the subject who favor the use of raw milk, 
 except when it is from dairies which are abso- 
 lutely above suspicion. 
 
 The important consideration which influences 
 authorities when they insist that milk be pasteur- 
 ized is of course the desire that the milk may be 
 free from dangerous bacteria. 
 
 *The Milk Question — M. J. Rosenau. 
 
 22 
 
FROM THE PRACTICAL VIEWPOINT 
 
 There are commercial reasons which influence 
 dealers, such as the desire to prevent the souring, 
 and thus the loss of milk, but these considerations 
 have little weight with health authorities. The 
 prevention of economic waste of food products has 
 a bearing upon the public health, and there are 
 indications that the personal interest which those 
 in authority have as men in these matters is being 
 extended to their oflficial interest. Care must be 
 observed, however, that these two considerations be 
 justly balanced. 
 
 The United States Government has endeavored 
 to reduce the losses which result from the condem- 
 nation of cream which is not considered fit to use 
 as cream. This is accomplished by partially de- 
 naturing it by the addition of salt, so that it can be 
 used for butter making. An attempt has also been 
 made to prevent the destruction of milk which has 
 a temperature above that fixed by the authorities 
 as legal. It is well known that in some cities this 
 drastic action is taken in order to secure proper 
 refrigeration. Such destruction of milk, which has 
 a high food value, should be looked upon as almost 
 criminal. 
 
 Careful experiments carried on by Park, Rose- 
 
 23 
 
THE PASTEURIZATION OF MILK 
 
 nau, and others have demonstrated the fact that 
 if milk is heated to a temperature of 140° F._, and 
 is held at this temperature for twenty minutes, or 
 even less, all of the pathogenic or disease-produc- 
 ing bacteria will be destroyed. Also, if the milk 
 is heated to a uniform temperature of 158° F., 
 and held thereat for one minute, all such disease 
 germs will be killed. Between these extremes, dif- 
 ferent degrees of temperature, and correspond- 
 ingly varying lengths of holding time, will pro- 
 duce equally good results. These experiments 
 have been carried on of course in laboratories 
 where ideal conditions for securing accurate re- 
 sults existed. Accurate temperatures could be ob- 
 tained and the length of time for which the milk 
 was held could be carefully controlled. When, 
 however, pasteurization is carried on under com- 
 mercial conditions, where large quantities of milk 
 are handled, the same amount of accuracy is not 
 possible. There are variations in temperature and 
 variations in the length of time for which it is 
 held, due largely to the mechanical defects or 
 limitations in all forms of machinery. These fac- 
 tors of error render the results uncertain, and it 
 is therefore desirable that the temperatures and 
 
 24 
 
FROM THE PRACTICAL VIEWPOINT 
 
 the lengths of time for holding, which in the labo- 
 ratory tests have been found to be effective, be 
 somewhat increased, in commercial practice. 
 
 Various cities have made regulations in this re- 
 spect which appear to best suit local conditions. 
 In New York City, when regulations were first 
 adopted concerning milk pasteurization, the length 
 of time for which milk must be held when heated 
 to 158° F. was officially fixed at no less than three 
 minutes, and if heated to 140° it must be held for 
 at least twenty minutes. Between these extremes 
 of temperature holding times were fixed which va- 
 ried between three minutes and twenty minutes. 
 
 Experiments were made by Schores and Rose- 
 nau * in which careful tests were carried on while 
 milk was being pasteurized in the ordinary way, 
 a commercial pasteurizer and holding device being 
 used. These tests were made for the purpose of 
 determining if the thermal death point of patho- 
 genic bacteria, as indicated by laboratory tests, 
 could be safely relied upon under commercial con- 
 ditions. In their experiments the investigators in- 
 troduced germs of tuberculosis, diphtheria, and 
 typhoid fever, into milk, which was then run 
 
 ♦The Journal of Medical Research Vol. XXVI No. 1. 
 
 25 
 
THE PASTEURIZATION OF MILK 
 
 through a commercial pasteurizer and heated to 
 different temperatures_, and held for varying lengths 
 of time. The results obtained indicated that when 
 an attempt was made to heat this milk in a com- 
 mercial pasteurizer to a temperature of 140° F., and 
 then hold it for twenty minutes, there was a con- 
 siderable unavoidable variation in the actual tem- 
 perature to which the machine was capable of 
 heating the milk. This was due to the difficulties 
 of both hand and automatic temperature control. 
 Even with the best automatic controller, it is 
 probable that the real variation of temperature is 
 greater than is indicated upon the record charts. 
 Thermometers are not usually sufficiently sensitive 
 to record rapid fluctuations in temperature. It is 
 also true that thermometers indicate average tem- 
 peratures only, and it is possible that certain por- 
 tions of the milk, the temperature of which is con- 
 siderably below this indicated average, pass 
 through the apparatus. 
 
 In regard to the time held also, especially when 
 a continuous or flow type holding apparatus is 
 used, great uncertainty exists. It is impossible to 
 be sure that the time is the same as intended. The 
 rate of flow varies, and there is also more or less 
 
 26 
 
FROM THE PRACTICAL VIEWPOINT 
 
 mixing of the milk due to various causes^ which 
 will be discussed later. 
 
 Schores and Rosenau found that pathogenic bac- 
 teria were not all killed when the factors of tem- 
 perature and time were attempted which had been 
 found effective in laboratory tests. They there- 
 fore recommended, in order to provide a sufficient 
 margin of safety, that all milk he heated to a 
 temperature of at least 145°, and there held for 
 no less than twenty-five minutes. This opinion is 
 shared by most persons who have made a study 
 of the subject. The New York City Department 
 of Health, in 1914, so modified its regulations as 
 to require that pasteurized milk be heated to from 
 142° to 145° F. for at least thirty minutes. 
 
 While the destruction of all pathogenic bac- 
 teria in milk is the primary concern of health au- 
 thorities, there are certain other considerations 
 which have weight with them, and among these 
 is the effect which heat has upon the chemical 
 characteristics of the milk. It has been found that 
 when milk is heated to say l60° F. or over, some 
 of the constituent parts of the milk are changed in 
 such a way as to make it somewhat inferior as a 
 food, especially for infants. These changes have 
 
 27 
 
THE PASTEURIZATION OF MILK 
 
 been somewhat extensively studied by the United 
 States Government experts^ and it has been found 
 that as the temperature rises above 160° F., these 
 changes take place to an increasing extent, and at 
 the boiling point quite extensive changes are ob- 
 served. At this temperature, the milk sugar be- 
 comes scorched, the casein and the albumin are 
 somewhat hardened, the calcium, magnesium and 
 phosphoric salts are partially precipitated, all of 
 which renders the milk less easily digested. It 
 therefore follows that the lowest temperature 
 which is consistent with the destruction of the 
 pathogenic bacteria is the most desirable. 
 
 It is also true that milk which contains an ex- 
 cessive number of bacteria carries with it, as a re- 
 sult of their growth, certain by-products, such as 
 acids and other undesirable substances, and may 
 also contain dangerous poisons. Rosenau states 
 that the known poisons which are produced by the 
 growth of bacteria in milk are very few, but that 
 such poisons may possibly exist and produce harm- 
 ful effects upon the persons using the milk. These 
 by-products of bacterial grovrth in milk are not 
 entirely destroyed by heating, even when the boil- 
 ing temperature is attained. For this reason it is 
 
 28 
 
FROM THE PRACTICAL VIEWPOINT 
 
 desirable that milk which is to be pasteurized shall, 
 before it is heated, be as free as possible from all 
 bacteria. It is this consideration which has led 
 health authorities to insist that the milk before pas- 
 teurization shall not contain an excessive number 
 of bacteria. 
 
 Milk dealers know that their customers com- 
 monly judge of the richness of the milk by the 
 amount of cream which appears upon the top of 
 the bottle. For this reason the showing of a 
 "good cream line" is one of the things for which 
 the milk dealer strives. In some parts of Europe 
 the cream is thoroughly mixed in the milk by 
 homogenizing it, so that the cream will not rise, 
 but the American housewife is not educated to this 
 custom, and therefore anything which interferes 
 with the apparent volume of cream on the milk is 
 a stumbling-block to the milk dealer. It has been 
 found that milk which is heated to a temperature 
 of 148° F. or over and is held for any consid- 
 erable period of time, will have its cream line de- 
 stroyed, or at least be made indistinct. When 
 milk is heated to a temperature lower than this 
 and is held for a great length of time, the same 
 effect is produced. There are other reasons which 
 
 29 
 
THE PASTEURIZATION OF MILK 
 
 interfere with the cream line which will be dis- 
 cussed later. 
 
 Another objection which customers urge against 
 pasteurized milk is that it has a distinctly 
 scorched or cooked taste. This is undoubtedly true 
 when the milk is heated to a high temperature, or 
 when an uneven temperature is maintained. If the 
 heating medium is kept at a point greatly above 
 the temperature to which the milk is to be raised, 
 the same effect is produced. On account of this 
 cooked taste it is evident that there is a commer- 
 cial objection to pasteurization where it is not 
 properly or carefully done. 
 
 Moreover, when a low temperature of heating is 
 used, the enzymes are not much affected, while 
 they are destroyed when a high temperature is ap- 
 plied. Indeed, the Storch test, which is used to 
 determine whether skim milk has been heated to 
 165° or higher in compliance with the laws in this 
 regard, depends upon the non-action of the en- 
 zymes. These are destroyed by high heating. 
 This test is of little or no value in testing milk 
 pasteurized at low temperature. 
 
 Since an even heating at comparatively low 
 temperatures and a holding for a long time secures 
 
 30 
 
FROM THE PRACTICAL VIEWPOINT 
 
 the desired result in the destruction of bacteria, 
 and at the same time produces none of the unde- 
 sirable effects which follow when, a high tem- 
 perature is employed, it is evident that this 
 method of procedure is that which is much to be 
 preferred. 
 
 To summarize the considerations which have 
 just been discussed, it is evident that the pastur- 
 ized milk which most nearly fulfills the require- 
 ments desired by health authorities, and at the 
 same presents, from the commercial aspect, the 
 least objections, must conform to the following de- 
 mands : 
 
 First: Before pasteurization it must contain only 
 a small number of bacteria. 
 
 Second: When it is heated it must be subjected 
 to a temperature which destroys all pathogenic or 
 disease-producing bacteria, and also a large per- 
 centage of bacteria of all other kinds. 
 
 Third: Its constituents must be very little 
 changed or altered by excessive heating. Its nu- 
 tritive value must not be impaired, and its diges- 
 tive enzymes must be uninjured. 
 
 Fourth: The taste of the milk must not be no- 
 ticeably changed. 
 
 31 
 
THE PASTEURIZATION OP MILK 
 
 Fifth: The apparent volume of cream must not 
 be reduced. 
 
 In so far as these factors represent results 
 which are properly demanded by health authori- 
 ties, there are, broadly speaking, two general 
 methods by which they can be controlled when 
 their control depends upon the powers exercised 
 by the municipality or the state. One of these 
 may be called the laboratory method, and the 
 other the inspectional method. When the labora- 
 tory method is employed it is necessary that cer- 
 tain definite chemical and bacteriological standards 
 be adopted, which apply to pasteurized milk or to 
 milk which is to be pasteurized. Some of these 
 standards may depend upon color reactions. Such 
 standards being in force, the effectiveness of con- 
 trol depends upon the frequent examination of sam- 
 ples of milk taken before and during the process 
 of pasteurization and as it is offered for sale. If 
 the tests show that the milk conforms to the legal 
 standards, it may be judged, with a fair degree of 
 confidence, that the apparatus employed in pas- 
 teurizing and handling the milk is properly in- 
 stalled and operated. 
 
 When the inspectional method of control is em- 
 
 S2 
 
FROM THE PRACTICAL VIEWPOINT 
 
 ployed, it is necessary that certain definite regula- 
 tions be adopted which shall specify on broad lines 
 the form of apparatus which must be used, how 
 it shall be installed and how it shall be operated. 
 The construction and arrangement of the build- 
 ings and of the various rooms may be specified, it 
 having been determined by previous experience 
 that such and such apparatus and surroundings 
 operated and handled in such and such a way will 
 produce milk which will be of the character de- 
 sired. With these regulations in force, it is pos- 
 sible, by frequent and careful inspections made of 
 pasteurizing plants, to determine whether or not 
 the legal regulations are being faithfully observed. 
 If it is found that they are complied with, then it 
 is logical and safe to conclude that the milk pro- 
 duced is of suitable character, and will satisfac- 
 torily respond to all suitable chemical and bac- 
 teriological tests which may be applied. 
 
 As a matter of fact, neither method of control 
 is used by authorities to the exclusion of the other, 
 but a combination of the two methods is found to 
 be the most satisfactory. In some cities the em- 
 phasis is placed upon laboratory tests, with in- 
 spections made to confirm the results. In other 
 
THE PASTEURIZATION OF MILK 
 
 places, the emphasis is upon physical regulations 
 and inspections, with occasional laboratory tests to 
 confirm the conclusions reached and to aid in the 
 discovery of obscure defects which may escape ob- 
 servation during the usual inspections. No advice 
 can be given as to which method is most desirable 
 without first knowing local conditions, taking into 
 account the extent of the milk industry, the avail- 
 able factors of men, money and laboratory equip- 
 ment, etc. Each community presents its individ- 
 ual problem. 
 
 Health authorities are often requested by milk 
 dealers to give advice as to the form of pasteurizing 
 apparatus which will perform the best work, or 
 they are asked what kind of machine the authorities 
 recommend. It is manifestly improper for health 
 authorities to recommend specifically any one or 
 more forms of apparatus as the best. If they did, 
 they would lay themselves open to the charge of 
 unfair favoritism, and to the suspicion that im- 
 proper influence determined their judgment. It 
 is only proper that they should state that in their 
 experience certain forms of apparatus, operated 
 in certain ways, have performed certain things in 
 actual practice which are or are not satisfactory 
 
FROM THE PRACTICAL VIEWPOINT 
 
 to those who are responsible for this condition of 
 the milk. Indeed, when advice is asked as to the 
 form of apparatus most desirable to be installed 
 at a given point, it is impossible to solve such a 
 problem without possessing complete knowledge of 
 the conditions which surround each plant where it 
 is desired to install a pasteurizer. Each plant 
 presents an individual problem of its own, which 
 must be carefully studied, having clearly in mind 
 all the facts which specially relate to the plant in 
 question. It is impossible to place too much em- 
 phasis upon this point, since time and money and 
 the securing of expert advice before the construc- 
 tion and equipment of a plant will frequently bring 
 continuous dividends in convenience, in the saving 
 of time, in preventing needless waste of money, 
 and in the general satisfaction which accompanies 
 the successful operation of an efficient plant. 
 
 Among the factors to be considered, the con- 
 struction and physical characteristics of the build- 
 ing where the plant is to be located is of impor- 
 tance in determining the selection of the appara- 
 tus to be used. Again^ the distance of the plant 
 from the point where the milk is to be distributed 
 and consumed should be considered. If located 
 
 S5 
 
THE PASTEURIZATION OF MILK 
 
 in the country at a distance from the city, the ele- 
 ment of time available after the milk is delivered 
 by the dairyman is also an important item. The 
 amomit of milk to be pasturized daily, and the 
 use which is to be made of the finished product 
 have a bearing upon the final decision. With 
 many dealers the question of expense may be of 
 first importance, but it must be borne in mind 
 that cheap installation does not always mean econ- 
 omy. The question of expense involves both the 
 initial cost of installation and the outlay for oper- 
 ation and upkeep. Where the matter of furnish- 
 ing sufficient steam is a point for serious con- 
 sideration, or where water expense affects the final 
 cost, it is desirable to use those forms of appara- 
 tus which consume the fewest heat units and which 
 use the least amount of water. There are also 
 other considerations which will be discussed later, 
 and it will be found that at many plants unique 
 conditions exist which must be carefully studied. 
 
 On broad lines, however, it may be stated that 
 a pasteurizing plant, in order to be as nearly as 
 possible ideal in regard to its construction, and 
 which will at the same time be capable of produc- 
 ing a milk which will be satisfactory from the 
 
 36 
 
FROM THE PRACTICAL VIEWPOINT 
 
 standpoint of safety and wholesomeness, and will 
 also satisfy commercial demands, should combine 
 the following features: 
 
 1. 2'he Building. — The building where the plant 
 is located should contain ample space and should, 
 if possible, be so arranged that the milk will flow 
 by gravity from the point of receipt, or where 
 cans are emptied to the point where it is taken out 
 for delivery or transportation. 
 
 2. Separate Rooms. — The various stages in the 
 process of treating the milk, such as receiving, 
 pasteurizing, cooling, filling containers, storage 
 and of washing the containers, should be carried 
 on in separate, clean, well-lighted and ventilated 
 rooms or compartments. 
 
 3. Protection from Contamination. — At all 
 points during the process of handling, the milk 
 should be protected against contamination from 
 contact with unclean apparatus, and from infec- 
 tion by means of dust-laden air. This protection 
 is especially necessary after the holding process 
 is completed. Any infection occurring after this 
 time is not corrected by heating, and may there- 
 fore be a source of danger. 
 
 4. Constant Temperature. — The heating appa- 
 
 «7 
 
THE PASTEURIZATION OF MILK 
 
 ratus, whatever its form, should be capable of 
 heating every particle of milk to a temperature 
 which will never be below that to which it is the 
 intention that it shall be heated. For instance, 
 if it is intended to heat to 140°, the temperature 
 should not fluctuate between 135° and 145°, but 
 should remain constantly at 140° or over. 
 
 5. Method of Heating. — The heating should be 
 accomplished by an apparatus which allows the 
 milk to flow over a clean metal surface, which is 
 kept hot by means of heated water, and not by 
 direct steam contact. This hot water should never 
 have a temperature more than 10° or 15° higher 
 than that to which it is desired to heat the milk. 
 
 6. Holding Apparatus. — The holding appara- 
 tus, whether the absolute or the continuous flow 
 type process is employed, should be so constructed 
 and operated that it will definitely insure the 
 holding of every particle of the milk without fail 
 for the desired length of time. 
 
 7. Recorders. — The temperature to which the 
 milk is heated must be automatically recorded, and 
 should be automatically controlled. It is desir- 
 able that a temperature recording device be in- 
 stalled at the point where the milk leaves the 
 
 58 
 
FROM THE PRACTICAL VIEWPOINT 
 
 heating apparatus and that another recorder be 
 attached to the outlet pipe from the holder. This 
 latter recorder indicates whether or not any great 
 amount of heat has been lost during the holding 
 process^ and also shows whether the apparatus is 
 thoroughly heated before the milk is admitted. If 
 not so heated, the first milk leaving the holder 
 will have been somewhat cooled, and the recorder 
 will indicate this. After the apparatus has been 
 in operation for a considerable time, it will then 
 acquire the temperature of the milk, which will 
 then pass out with the temperature but little di- 
 minished. These observations do not apply to a 
 tank or batch pasteurizer. In this case a single 
 recorder attached to the tank itself shows all that 
 is necessary. It also indicates the time for which 
 the milk is held at the required temperature. 
 
 8. Pumps and Pipings. — The amount of milk 
 piping in use should be reduced to the minimum 
 requirements. All piping which is used should 
 be of sanitary construction, with the joints and 
 turns so arranged that they can be easily taken 
 apart for cleaning. As before stated, the appara- 
 tus should be so arranged that the milk will flow 
 by gravity from point to point in the process of 
 
 S9 
 
THE PASTEURIZATION OF MILK 
 
 treatment. If, however, it is necessary to use milk 
 pumps, they should be of absolutely sanitary con- 
 struction. The use of pumps for moving the raw 
 milk is less objectionable than is their use for mov- 
 ing pasteurized milk. Not only is the danger of 
 infection by means of unclean pumps very serious, 
 but if the milk is pumped while hot, the cream is 
 so disturbed that it does not rise as readily as is 
 desirable. 
 
 9. Rubber Fittings and Gaskets. — The use of 
 rubber fittings, of gaskets and of stuffing-boxes 
 should be avoided. 
 
 10. Cooling. — The milk should be immediately 
 and rapidly cooled, to a temperature as nearly 
 40° F. as possible. This cooling should be accom- 
 plished within thirty minutes after the heating and 
 holding process is completed. Except where cool- 
 ing is carried on in the tanks where it is heated, 
 the cooling can be completed in much less than 
 thirty minutes. The milk should be, of course, 
 kept cold until delivered to the consumer. 
 
 11. Cleaning of Containers. — All containers, 
 including cans, covers and bottles, should be com- 
 pletely and if possible automatically washed and 
 sterilized. They should then be thoroughly dried 
 
 40 
 
FROM THE PRACTICAL VIEWPOINT 
 
 and should be stored in clean, cold rooms, and there 
 kept inverted or carefully covered until filled. 
 
 12. Cleaning of Apparatus. — All apparatus 
 used in handling milk should be carefully washed 
 and sterilized after its use, and all of it which 
 comes in contact with the pasteurized product 
 should be again sterilized before its use each day. 
 
 13. Healthy Employees. — All persons employed 
 in handling the milk should be known to be healthy 
 and free from any infectious disease. They 
 should be clean in their person and habits, and 
 should wear special clean clothing, preferably of 
 white material, while handling milk. 
 
 lit. Bottle Capping. — The milk bottles, after 
 filling, should be capped by clean machinery, thus 
 avoiding as far as possible any personal contact 
 with the milk after it is pasteurized. 
 
 It is needless to say that all the ordinary precau- 
 tions regarding the sanitary construction of build- 
 ings where food is handled should be observed, 
 and the close proximity of stables or other con- 
 taminating influences should be avoided. 
 
 There are, of course, many other points of de- 
 tail in the construction and operation of pasteur- 
 izing plants which will repay careful attention. 
 
 41 
 
THE PASTEURIZATION OF MILK 
 
 These will be touched upon in the following pages. 
 On broad lines, however, it may be said that if the 
 foregoing conditions are carefully fulfilled, then 
 it will be possible to obtain a good safe milk which 
 the public may consume with a feeling of security, 
 and which should satisfy all requirements of health 
 authorities. 
 
 It is not proper, of course, to recommend any 
 specific type or form of apparatus to be used in 
 pasteurizing milk. It is proposed, however, to de- 
 scribe in the following pages and to show by dia- 
 gram or illustration the construction and operation 
 of different makes of apparatus, and to call atten- 
 tion to those points in each which experience has 
 taught are of advantage or disadvantage. 
 
 42 
 
CHAPTER II 
 
 HEATERS 
 
 In 1909 the New York City Department of 
 Health first adopted the rule which required that 
 milk could not be considered as pasteurized un- 
 less it had been heated to a definite temperature 
 and held at this temperature for a certain definite 
 length of time. New York was the pioneer in 
 requirements of this sort. 
 
 At this time various forms of milk heaters were 
 on the market, but no device was available for 
 holding the heated milk. All heaters employed 
 a process which is known as the continuous or flash 
 process of heating. By this process the milk 
 flowed or was forced in a continuous stream 
 through the apparatus, where it was subjected to 
 an amount of heat which was not very definite, and 
 which was controlled by the hand of the operator. 
 The milk was then immediately cooled. 
 
 Most of the forms of apparatus which were 
 then on the market are still in use, and certain new 
 forms of heaters have been invented. Certain new 
 types of apparatus were devised as adjuncts of 
 
 43 
 
THE PASTEURIZATION OF MILK 
 
 the heaters, into which the milk was allowed to 
 flow from the heaters and in which the hot milk 
 was held for the time required by the regulations. 
 
 As before stated, the forms of heaters in use 
 in 1909 are still employed, with certain new forms 
 made by many different manufacturers. They are 
 all comprised under some one of five typical forms, 
 as follows: 
 
 First Type. — The so-called Danish heater is 
 sold by various firms. It is shown in the accom- 
 panying illustrations (Figs. 1 and 2). This is 
 the oldest form of heater in use in this country. 
 In this form a large central cylinder is provided 
 with a double cover or jacket. The space between 
 the inner and outer shell is filled with water, into 
 which steam is introduced. By means of a 
 suitable device the steam is distributed through the 
 water at various points. 
 
 In operation, the milk is allowed to flow or is 
 pumped into the inner compartment or cylinder, 
 and by means of rapidly revolving paddles it is 
 thrown by centrifugal force against the inner sur- 
 face of the cylinder. This surface is kept hot by 
 means of the hot water and steam in the outer 
 shell. The milk enters at the bottom of the cylin- 
 
 44 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Fig. 1 
 
 Fig. 2 
 
 der, and since the outlet pipe at the top is placed 
 at a tangent to the cylinder^ the rotating paddles 
 tend to throw the milk out of the pipe. The ma- 
 chine therefore acts somewhat as a pump, and 
 when the whole machine is set at an angle from 
 the perpendicular, this tendency to throw the milk 
 is enhanced and the milk can be lifted about fifteen 
 feet. This fact is one of the advantages of the 
 machine. Another advantage is that it is com- 
 paratively inexpensive, since it is rather small. Its 
 
 45 
 
THE PASTEURIZATION OF MILK 
 
 size also tends toward the ease of cleaning, there 
 being no great amount of surface with which the 
 milk comes in contact. 
 
 This very fact, however, that the heating sur- 
 face is small in area, is also a disadvantage, for 
 it renders it necessary to raise the temperature of 
 the heating medium to a point so high that it is 
 frequently very much in excess of that to which 
 it is the desire to heat the milk. The result is 
 that certain portions of the milk reach a tempera- 
 ture so high that a distinctly scorched taste is im- 
 parted to it. This taste persists in the entire 
 body of the treated milk, even though the average 
 temperature of the milk leaving the apparatus is 
 below 145°. This is especially noticeable if the 
 flow of milk into the apparatus fluctuates. It can 
 be readily seen that with a very hot heating sur- 
 face, and at the same time a small amount of milk 
 passing through the machine due to a sudden stop- 
 page of flow, this milk would attain a high tem- 
 perature. 
 
 This superheating of even a portion of the milk 
 tends to cause an interference with the normal 
 rising of the cream, after the milk is placed in 
 containers. The vigorous agitation of the hot milk 
 
 46 
 
FROM THE PRACTICAL VIEWPOINT 
 
 by means of the paddles also has a tendency to 
 break up the fat globules into smallei particles, 
 which do not so readily rise to the surface. 
 
 It is difficult to maintain a uniform temperature 
 with this type of machine, since the amount of 
 heating fluid is comparatively small, and when 
 there is either a fluctuating flow of milk or a vary- 
 ing milk temperature, there is no automatic con- 
 troller which can be made to respond to sudden 
 changes in temperature quickly enough to check 
 or increase the flow of steam into the heating 
 chamber. 
 
 As a general proposition, also, the introduction 
 of steam directly into a heating chamber is to be 
 avoided, since there is always the possibility that 
 certain portions of the steam will strike the heat- 
 ing surface before becoming condensed, and will 
 therefore heat these portions to an abnormally 
 high point. 
 
 Second Type. — There are several heating de- 
 vices made by different firms, and having certain 
 variations in the details of their construction, 
 which embody the same general principles. These 
 are illustrated in Figs. 3, 4, 5. In all of these 
 the milk flows between two or more upright, heated 
 
 47 
 
THE PASTEURIZATION OF MILK 
 
 Fig. 3 
 
 1 — Discharge of warmed milk to gathering tank. 
 
 2 — Return of warmed milk to interior of heater. 
 
 3 — Discharge of heated milk to holder. 
 
 4 — Hot water intake. 
 
 5 — Return of held milk to regenerator. 
 
 6 — Cold milk entering heater. 
 
 7 — Discharge of partly cooled miik to cooler. 
 
 48 
 
FROM THE PRACTICAL VIEWPOINT 
 
THE PASTEURIZATION OF MILK 
 
 Fig. 4-B 
 
 cylindrical surfaces. The heating surfaces are 
 kept at the desired temperature by means of hot 
 water, which in turn is heated either by the intro- 
 duction of steam into the water chamber directly, 
 or by heating the water in tanks outside the milk 
 
 50 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Milk 
 Outlets 
 
 Fig. 5 
 
 1 — Interior water tank. 
 2 — Exterior water tank. 
 3 — Space between water tanks, through which milk is forced upward. 
 
 51 
 
THE PASTEURIZATION OF MILK 
 
 apparatus. From these tanks it is pumped into 
 the heating chambers. Where steam enters di- 
 rectly into the milk apparatus the same objections 
 obtain which were noticed in the description of the 
 Danish type of heater. Superheating of the milk 
 in whole or in part, an objectionable cooked taste, 
 interference with the cream line, etc., are likely to 
 follow. Where an outside heating tank is employed, 
 it is comparatively easy to keep the water at a 
 nearly uniform temperture by means of a thermo- 
 stat, which controls the introduction of steam. 
 With this heated water being pumped to the milk- 
 heating apparatus, it is certain that the milk can 
 never get above the temperature to which the water 
 is heated, and if this water is not more than 10° or 
 15° hotter than the temperature at which it is the 
 intention to heat the milk, no serious superheating 
 can result. This point will be more fully de- 
 scribed later. 
 
 In all heaters of this type some method is em- 
 ployed to keep the milk in constant motion as it 
 flows upward between the heating surfaces, thus 
 insuring that all portions of milk come in contact 
 with their surfaces. In the machine illustrated in 
 Fig. 3 this agitation is accomplished by means of 
 
 52 
 
FROM THE PRACTICAL VIEWPOINT 
 
 a revolving arm, which extends into the milk space 
 between the inner and the outer water chambers. 
 In Fig. 5 J the inner cylinder revolves and the nar- 
 row corrugation which extends in a spiral form 
 around the cylinder forces the milk upward. The 
 shaft which operates these stirring devices in some 
 instances comes in contact with the milk, and in 
 order to prevent leakage, it is necessary to pro- 
 vide some sort of packing or stuffing box. This 
 is a disadvantage, since nearly all packing is some- 
 what porous, and it is difficult to keep clean. 
 
 Heaters constructed in this general form have 
 been found to be effective in operation, and good 
 results have been obtained by their use. They 
 have been found to be durable as well. Some in- 
 dividual machines have been in use for ten years, 
 which indicates the carefulness with which they 
 have been constructed. Those forms of heaters 
 are the most satisfactory in which the greatest 
 amount of heating surface is available, and where 
 the amount of hot water which circulates through 
 the apparatus is relatively large. These conditions 
 render it possible to use water which has a com- 
 paratively low temperature. 
 
 Some of these heaters employ what is known 
 
 53 
 
THE PASTEURIZATION OF MILK 
 
 as the "regenerative principle." This means that 
 the hot milk which flows from the machine is em- 
 ployed for warming the cold milk which flows into 
 the apparatus to be heated. When this regenera- 
 tive principle is used, a considerable economic sav- 
 ing of heat units is secured. This saving means 
 that less steam is required for heating, and also that 
 less ice is necessary for cooling. In the type illus- 
 trated in Fig. 4 the milk flowing from the holder 
 is conveyed to a holding apparatus, and after be- 
 ing held is returned to the heater, where it flows 
 through another compartment and helps to heat 
 the inflowing cold milk. 
 
 At least one form of regenerative heater (Fig. 
 6) is so constructed that this intermediate holding 
 process cannot be used. In sections of the country, 
 therefore, where city regulations require that the 
 heated milk be held for a definite period, this form 
 of heater cannot be used. As a so-called "flash" 
 pasteurizer, this machine has given good results. 
 
 In Fig. 4-B is shown a form of heater in which 
 the hot water is contained on the inside of the lower 
 cone. The milk flows from the top over the heated 
 cone. Revolving arms to which is attached a heavy 
 cord, keep the cone surface wiped, and prevent 
 
 .54 
 
FROM THE PRACTICAL VIEWPOINT 
 
 d 
 
 M 
 
 55 
 
THE PASTEURIZATION OF MILK 
 
 the milk from sticking to the heated surface. 
 There is difficulty in keeping the cord clean and 
 sanitary. 
 
 Third Type. — The tubular type of heater is 
 manufactured and sold by several concerns. In 
 all of these forms, the milk flows through tubes, 
 which are themselves surrounded by some heating 
 medium, usually hot water. In the form shown 
 in Fig. 7 the milk tube is enclosed by a larger 
 tube, through which hot water flows in a direction 
 opposite to the milk flow. In forms which are 
 illustrated by Figs. 8, 9 and 10 the heating water 
 is contained in boiler-like structures, through 
 which the tubes extend. Care must be exercised 
 in order to make sure that there can be no leak- 
 age between the milk tubes and the water con- 
 tainers. In Fig. 7 the couplings between the vari- 
 ous milk pipes in the series are outside of and 
 beyond the water couplings, so that no mixing of 
 the milk and water can occur unless there is a 
 broken milk pipe. In Figs. 8, 9 and 10 the milk 
 tubes are either braized or expanded into the heads, 
 and the danger of leakage is slight. Of course, 
 when heat is applied to these tubes, the tendency 
 is for them to expand and so become more tightly 
 
 5Q 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Fig. 7 
 
 fixed in the heads. Sudden and wide variations of 
 temperature would tend to loosen the joints. The 
 flowage of the water in a direction opposite to milk 
 flow brings the hottest water against those milk 
 tubes where the hottest milk is found. As the 
 
 57 
 
THE PASTEURIZATION OF MILK 
 
 Fig. 8 
 
 water flows along the tubes it becomes gradually 
 cooled by the cooler milk^ so that it emerges at a 
 low temperature. Thus the milk is heated grad- 
 ually, and no sudden raising of the temperature 
 occurs. This renders the control of the tempera- 
 ture an easy matter, since sudden fluctuation in 
 temperature cannot readily occur. There is also 
 
 58 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Fig. 9 
 
 an economical use of the heat, and little of it is 
 wasted. 
 
 In Fig. 11 a form of heater is illustrated in 
 which the milk flows through a group of small 
 tubes, which are themselves enclosed in a large 
 
 59 
 
THE PASTEURIZATION OF MILK 
 
 60 
 
FROM THE PRACTICAL VIEWPOINT 
 
THE PASTEURIZATION OF MILK 
 
 tube. The larger tube contains the water which 
 surrounds the small tubes which contain the milk. 
 When the regenerative principle referred to is em- 
 ployed, in this type of heater the hot milk return- 
 ing from the holding tanks is allowed to flow 
 through the larger tube, and thus assist in heating 
 the cold inflowing milk. 
 
 Tubular heaters are doing very satisfactory 
 work. Those machines are in some respects the 
 most efficient in which the flow of milk is slow 
 enough or which have a sufficient heating surface 
 to insure that all portions of the milk will reach 
 the maximum temperature. It has been found 
 from experience that when milk flows through 
 tubes which are of comparatively large diameter, 
 there is a tendency for that portion of the milk 
 which is in the center of the tube to flow faster 
 than that which is close to the inner surface of 
 the tube. This is due to the greater friction at 
 the point of contact. It can be readily seen that 
 there will therefore be a tendency for the milk 
 which flows more slowly close to the heated surface 
 of the tube to become heated to a considerably 
 higher point than that near the center. When 
 the water entering the final tube of the heater is 
 
 62 
 
FROM THE PRACTICAL VIEWPOINT 
 
 high in temperature, there is a certain amount of 
 danger of cooking or scorching the milk, and pos- 
 sibly of breaking up the fat globules. It is also 
 true that if a coating of cooked milk forms on the 
 inner surface of the tube, it acts as an insulating 
 material and therefore a constantly increasing tem- 
 perature must be applied to the water. The return 
 of the milk from one tube to another in the series 
 tends to mix the milk and so break up the more 
 rapid flowing core. This breaking up process, 
 however, may have a detrimental effect upon the 
 fat content and may render the cream less likely 
 to rise. In one or two instances known to the 
 writer it was found that when the milk left the 
 apparatus at a temperature of only 140° the cream 
 line was considerably interfered with. 
 
 The types shown in Figs. 7, 10 and 11 have this 
 advantage, namely, that since they can be obtained 
 in sections, the pasteurizing plant can be expanded 
 by the installation of additional sections as the 
 growth of the business demands. Since a cooling 
 apparatus of exactly similar form is provided it is 
 possible to extend the cooling facilities in the same 
 way. By a proper interchange of the water used 
 in both the heater and cooler, the regenerative 
 
 63 
 
THE PASTEURIZATION OF MILK 
 
 principle is made use of, and the cool water leav- 
 ing the heater is carried over to the cooler, so that 
 it helps to cool the hot milk flowing into it. 
 
 In choosing a machine of this type, care should 
 be exercised in securing one which may be easily 
 cleaned, especially at the turns and joints. All 
 these should be smooth and readily accessible. 
 
 It should be borne in mind that while a large 
 heating area with many pipes is an advantage in 
 securing an even heating with a low water tem- 
 perature, the difficulties of cleaning are also in- 
 creased. 
 
 It is also readily seen that when powerful pumps 
 force the hot water rapidly through the heating 
 pipes, a relatively lower heating temperature may 
 be employed. 
 
 An objection to the tubular form of heater lies 
 in the fact that the tubes in this system are nearly 
 'liorizontal and parallel. There is thus but little 
 inclination or pitch to the tubes, and the milk flows 
 from them rather slowly when they are emptied at 
 the close of operations for the day. This objec- 
 tion has been overcome in some of the more re- 
 cently manufactured machines, by putting the 
 pipes at an incline and not parallel to each other. 
 
 64s 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Thus the milk can be more readily drained from 
 the apparatus when it is being emptied. 
 
 One striking advantage of the tubular type of 
 apparatus is found in the fact that it may be very 
 thoroughly sterilized. Steam can be admitted into 
 all the parts where the milk will enter, and the 
 steam may be under pressure if so desired. 
 
 It is important that a machine of this type be 
 so constructed that no milk will leak from one 
 section of tubing into another section, but that it 
 all follows the course which it is intended that it 
 shall follow. In the forms shown in Figs. 8, 9 
 and 10, the doors at the ends which cover the ends 
 of the milk tubes are provided with gaskets to 
 prevent this leakage. 
 
 It is well to note whether or not these gaskets 
 are tight. In one or two forms, the gaskets con- 
 sist of sheets of metal which are backed by felt 
 or rubber in such a way that the metal readily 
 conforms to the projections of the tubes, thus mak- 
 ing a closely fitting cover. The metal sheet can, 
 of course, be readily cleaned. 
 
 Fourth Type. — The tank, or so-called batch sys- 
 tem of heating milk, is quite largely employed. 
 Heating tanks for this purpose are now manu- 
 
 Q5 
 
THE PASTEURIZATION OF MILK 
 
 66 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Fig. 13 
 
 factored by many concerns which handle pasteur- 
 izing apparatus. These batch pasteurizers consist, 
 as shown in Figs. 12, 13, 14-, 14-B, 15, 1 6, of hori- 
 zontal tanks, constructed sometimes singly and 
 sometimes made with two compartments in the same 
 apparatus. In Fig. 16 we see a tank which is in the 
 form of an upright cylinder. These tanks are in 
 some cases surrounded by an insulating jacket. 
 In others there is an open space between the inner 
 and outer shell, through which hot water is made 
 
 67 
 
THE PASTEURIZATION OF MILK 
 
 
 68 
 
FROM THE PRACTICAL VIEWPOINT 
 
THE PASTEURIZATION OF MILK 
 
 to circulate, usually by means of a pump. These 
 tanks have, extending through them in a horizon- 
 tal direction, some form of agitator. This may be 
 a tubular coil, as in Figs. 12, 13 and 14-B, or stir- 
 ring paddles, as in Fig. 15, or it may be coil sus- 
 pended from above, as in Fig. l6. Some of the 
 older forms have, instead of a coil of pipe, a series 
 of hollow screw-shaped discs. In some, as in Fig. 
 14, there is a tubular structure which is suspended 
 from the top of the tank and which swings back 
 and forth by means of a mechanical arrangement. 
 In operation, these tanks being filled with milk, 
 hot water is forced through the tubes or discs 
 above referred to. These coils rotate, keep the 
 milk mixed and, at the same time, heat it and thus 
 raise it to the desired temperature. The circulation 
 of water is maintained in some machines by means 
 of pumps, the steam for heating being admitted 
 into the return water shortly before it is again 
 forced through the coil. 
 
 In other machines, as in Fig. 12, the admission 
 of air into the coil creates a suction which forces 
 the water through without the use of pumps. In 
 the form shown in Fig. 15, the heating is accom- 
 plished in a rather novel manner. In the space 
 
 70 
 
FROM THE PRACTICAL VIEWPOINT 
 
 6 
 
 71 
 
THE PASTEURIZATION OF MILK 
 
 between the inner and outer shell, there are placed 
 near the top two perforated pipes, into which hot 
 water is forced. The water is thrown through 
 the perforations, in jets, against the outer surface 
 of the inner shell. It flows down, following the 
 contour of the tank, and drops from the bot- 
 tom, from whence it is again pumped through 
 the pipes after being reheated. The milk in the 
 meantime is kept in agitation by means of the 
 paddles. 
 
 In any of these tanks it usually requires from 
 fifteen minutes to twenty-five minutes to raise the 
 milk from 50° to a temperature of 145°. The 
 proper temperature having been attained, the steam 
 is shut off, and the milk is allowed to remain hot 
 in the tank for any desired length of time. 
 
 The tank form of pasteurizer in practice shows 
 excellent results. In plants where there are large 
 quantities of milk to be pasteurized it is necessary 
 that two, three or more tanks be arranged in se- 
 ries. This insures a continuous flow of milk 
 through the cooling apparatus and the filling de- 
 vices. In actual operation with three tanks, it 
 occurs that while one tank is being emptied after 
 heating and holding, the milk is being held in the 
 
 72 
 
FROM THE PRACTICAL VIEWPOINT 
 
 second tank, while in the third tank the milk is 
 flowing in and is being heated. These operations 
 are repeated in rotation. 
 
 Many tests have shown that if the water in the 
 heating coils is heated by injecting steam directly 
 into the heating coil, the temperature at the inlet 
 end is rarely above l65°. It may occasionally 
 reach 175°. Usually it is sufficiently low so that 
 the milk is not injured by superheating. It can be 
 readily seen that the temperature at the inlet end 
 of the coil is much greater than at the outlet end, 
 since the cold milk takes up the heat, therefore the 
 heating efficiency of the coil is not equally great 
 for its entire length. Some attempts have been 
 made to improve matters by placing a smaller per- 
 forated coil inside the larger pipe, so that the 
 water distributed through the coil would have the 
 same temperature in its entire length. 
 
 An objection to the submerged coil is that it be- 
 comes necessary to have the bearings packed with 
 some sort of a stuffing-box. Stuffiing-boxes are 
 always a source of possible danger both on account 
 of the absorption of milk, which renders cleaning 
 difficult, and on account of the fact that the con- 
 stant attrition of the metal at the point of bearing 
 
 7S 
 
THE PASTEURIZATION OF MILK 
 
 creates a condition whereby a metallic taste may- 
 be imparted to the milk. 
 
 In the form shown in Fig. 15 the objections 
 due to uneven heat distribution are at least partly 
 overcome, since the heat is the same at both ends 
 and on both sides of the tank. 
 
 In Figs. 15 and 16 there are no bearings in the 
 milk, and stuffing-boxes are therefore eliminated. 
 
 It is obvious that when pumps of large capacity 
 force the water rapidly through the coils, the tem- 
 perature will be more nearly uniform throughout 
 the entire length, and a lower initial temperature 
 can be employed. 
 
 In plants where a comparatively small amount 
 of milk is to be pasteurized, as frequently occurs 
 in country shipping stations, one or two tanks will 
 hold all the milk which is received at a plant each 
 day. It is therefore possible to use the tank for 
 several purposes. First, as a dumping tank for 
 receiving the milk; second, as a heater; third, as 
 a holding apparatus; fourth, as a cooler, since by 
 replacing the hot water by ice water or brine in 
 the coils, the milk can be cooled in the same tank. 
 Fifth, cans can be filled directly from these tanks. 
 In using the tank as a cooler, however, it is found 
 
 74 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Fig. 16 
 
 75 
 
THE PASTEURIZATION OF MILK 
 
 that the time required is usually considerably over 
 thirty minutes, which is longer than most authori- 
 ties will allow. In some instances the writer has 
 found that from an hour to an hour and a half 
 was required. Where brine can be circulated rap- 
 idly through the coil, this time can be considerably 
 reduced, especially if the coil is large. Some spe- 
 cial tanks are provided with unusually large coils. 
 In plants which are at a considerable distance 
 from the point where the milk is consumed, the 
 tank system of pasteurizing has this added advan- 
 tage. It is not always possible to get the milk into 
 the creamery from the patrons and to pasteurize 
 it before the departure of the milk train. In some 
 localities the regulations of the authorities specify 
 that pasteurized milk must be sold within from 
 twenty-four to thirty-six hours after pasteuriza- 
 tion. At these distant points it therefore becomes 
 necessary to hold over some raw milk from day to 
 day. If a pasteurizing system other than the tank 
 system is employed, this raw milk is stored in 
 cans, and a considerable amount of extra labor is 
 required to handle them. If the tank is used, the 
 milk which is received on one day may be placed 
 in the tank and there stored till the following 
 
 76 
 
FROM THE PRACTICAL VIEWPOINT 
 
 morning, it being kept cold in the meantime by 
 the circulation of cold water through the coils. 
 This milk may be heated on the morning of pas- 
 teurization as early as necessary to get it ready 
 for shipment, no handling or transfer of the milk 
 being previously necessary. 
 
 In case the tank is used as both a heater and a 
 cooler, there is of course a considerable strain 
 upon the joints of the apparatus due to the expan- 
 sion and contraction of the metal. Those forms of 
 apparatus are therefore the most desirable which 
 are the most strongly constructed, and are there- 
 fore least liable to break. A coil of pipe is 
 stronger than a screw disc. 
 
 Fifth Type. — Another process which has been 
 used to a limited extent for pasteurized milk is 
 known as bottle pasteurizing. By this method, the 
 bottles are filled with cold milk and are hermeti- 
 cally sealed. They are then either placed in a 
 tank, where they are submerged in water, or else 
 they are carried under showers of water. In either 
 case the temperature of the water increases as 
 the bottles are carried forward. When the de- 
 sired temperature is reached, the bottles are then 
 held for the desired time and are then brought 
 
 77 
 
THE PASTEURIZATION OF MILK 
 
 in contact with cold water, either in tanks or 
 in showers, till the temperature is sufficiently 
 reduced. 
 
 There is little doubt that from the purely theo- 
 retical point of view the pasteurization of milk in 
 the bottle is the ideal method. During the process 
 not only the bacteria contained in the milk are de- 
 stroyed, but also whatever bacteria may have been 
 contained in the bottles and on the caps are also 
 killed. It can also be seen that the danger of 
 recontamination after pasteurization is reduced to 
 the minimum. 
 
 There are several forms of apparatus on the 
 market in which the pasteurization takes place in 
 the bottle, two of which are shown in Figs. 17 and 
 18. This method of treatment is very extensively 
 used in the manufacture of beer. In Fig. 17, the 
 cases filled with bottles of the milk are carried by 
 an endless chain conveyor through several tanks 
 of water in succession. The water in the first tank 
 is warm, is hotter in the next, and so on till the 
 maximum is reached, after which the milk is car- 
 ried into the cooling tanks. The entire process 
 requires an hour or more. 
 
 In the process shown in Fig. 18, an endless plat- 
 
 78 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Fig. 17 
 
 :W^>y^'^r/^^'^ 
 
 79 
 
THE PASTEURIZATION OF MILK 
 
 Fig. 18 
 
 form carries the cases of bottles under showers of 
 water, of varying temperatures. 
 
 When milk is pasteurized by this method, a more 
 complete cooling is necessary than is the case with 
 
 80 
 
FROM THE PRACTICAL VIEWPOINT 
 
 beer. More cooling tanks or additional showers 
 are therefore required. 
 
 In a rather new machine, not shown in this book, 
 the bottles are placed in a thoroughly insulated box 
 or compartment, where they are subjected to a 
 shower of water, the temperature of which is in- 
 creased or decreased at will by proper regulating 
 devices on the outside of the apparatus. It is 
 claimed that with this outfit the heating and cool- 
 ing is rapidly accomplished, and that the com- 
 plete insulation of the compartment prevents the 
 loss of heat. It is also said that, for the same rea- 
 son, the same apparatus can be used as a cold 
 storage box, and the treated milk can be allowed 
 to remain in the apparatus after the completion 
 of the process till it is ready to be taken out for 
 delivery. These claims would seem to make it an 
 especially desirable outfit for small dealers, and 
 for dairymen in or near the cities where the milk 
 is to be sold. 
 
 The objections which are advanced against 
 the process of bottle pasteurization are, f,rst, that 
 the cap which it is necessary to use upon the bot- 
 tles in order to secure a tight seal is expensive; 
 too much so to warrant its use upon milk which is 
 
 81 
 
THE PASTEURIZATION OF MILK 
 
 sold at tlie popular price. It can, however, be 
 used on bottles containing milk sold at advanced 
 prices, like Certified Milk, Grade A, etc. The 
 second objection is that since the milk expands 
 upon being heated, the bottles cannot be entirely 
 filled. The bottles must therefore be made of a 
 size especially large, and customers must be 
 taught that bottles which are not full do still in 
 fact contain the full measure of milk. A third 
 objection advanced has been that milk in bottles 
 which are not full is more likely to become shaken 
 up, and the cream disturbed, than is the case in 
 bottles completely filled. This objection is 
 probably not of serious moment. A fourth and 
 rather serious objection is that the expense in the 
 consumption of heat units is much greater than 
 when other methods of pasteurizing are employed. 
 The reason for this is that the mass of glass in 
 the bottle nearly equals the mass of the milk, and 
 that since both bottle and milk must be heated 
 and also cooled, nearly double the amount of heat 
 is necessary, and a proportionately great amount 
 of cooling medium is used. In large plants this 
 added expense is very considerable. 
 
 An attempt has been made to overcome this last 
 
 82 
 
FROM THE PRACTICAL VIEWPOINT 
 
 objection, in part at least, by providing a series 
 of tanks shown in Fig. IQ. The five tanks shown 
 in line No. 1, 2, 3, 4, 5 are used for containing 
 the cases of filled bottles which are to be heated. 
 These are lowered into the tanks by suitable de- 
 vices. The other three tanks behind the pas- 
 teurizing tanks contain the water to be used in the 
 process. One, A, contains hot water, which is 
 kept at a constant temperature by means of a 
 thermostat. From this tank the water is circu- 
 lated by means of a pump through the tank, which 
 at the time contains the bottles which are being 
 heated and held. 
 
 A second tank, C, contains cold water, which is 
 kept cold either by ice or by a brine coil. This 
 water is circulated by a pump through the pas- 
 teurizing tank, in which at the time are contained 
 the bottles which were being cooled. 
 
 The third tank, C, is called a tempering tank. 
 The water in this is used for regenerative pur- 
 poses, in the following manner: After a tank full 
 of bottles has been heated and held for the de- 
 sired length of time, the hot water is all returned 
 to the heating tank, rendering the bottle tank 
 empty of water. Cool water from the tempering 
 
 83 
 
THE PASTEURIZATION OF MILK 
 
 tank is then admitted. This cools the hot bottles 
 of milk to a certain extent, and is in turn partly 
 heated. The water is then returned to the tem- 
 pering tank, after which the cold water from tank 
 C is pumped into the tank full of partially cooled 
 bottles, and when the cooling is complete, the bot- 
 tles are removed, and the tank is filled with fresh, 
 unpasteurized bottled milk. The warm water from 
 the tempering tank, then being admitted, it begins 
 to warm the cold bottles and is itself cooled. 
 After its return to the tempering tank it is ready 
 to be used again in the routine which has been 
 described, the process being repeated indefinitely. 
 In this way a large amount of heat is saved which 
 would be otherwise wasted. 
 
 From the illustration and the description the im- 
 pression is gained that this apparatus would be 
 rather cumbersome to operate, although it would 
 no doubt be possible to somewhat simplify the me- 
 chanical arrangements for shifting the water from 
 tank to tank. The writer is not personally fa- 
 miliar with any plant where such an arrangement 
 is in use. 
 
 Another method has been devised for saving 
 some of the heat otherwise wasted. This consists 
 
 84 
 
FROM THE PRACTICAL VIEWPOINT 
 
 r— ( 
 6 
 
 85 
 
THE PASTEURIZATION OF MILK 
 
 in heating the milk in any good form of pasteuriz- 
 ing apparatus, and then pouring it, while hot, into* 
 bottles which have just emerged in a hot condition 
 from this sterilizing apparatus. The heat which 
 is usually lost in cooling the hot bottles is in this 
 way saved. Since, however, the bottles must in 
 any case be cooled, it can be seen that the cooling, 
 which usually takes place slowly in the air when 
 washed bottles are stored in the ordinary way, 
 must now be accomplished rapidly in order to re- 
 duce the milk to the proper temperature in the 
 time required. This necessitates the use of ice 
 water or brine refrigeration, and since the volume 
 of glass used equals the volume of the milk, dou- 
 ble the amount of cooling medium is required than 
 when only the milk is cooled. 
 
 Experiments were made by Ayers and Johnson 
 in which the heated milk in bottles received a pri- 
 mary cooling by means of blasts of air at ordinary 
 temperatures. These experiments indicated that 
 a considerable economical saving of cooling medium 
 thus could be effected. Completing the cooling by 
 means of blasts of chilled air produced satisfac- 
 tory results. The fact that the cooling process 
 required a long time seemed to produce no harm- 
 
 86 
 
FROM THE PRACTICAL VIEWPOINT 
 
 ful effects upon the milk. There was no noticeable 
 increase in bacterial content when the cooling was 
 accomplished within two hours. These results 
 were obtained under conditions which somewhat 
 approached what might be termed laboratory sur- 
 roundings, and it is possible that under the stress 
 of commercial conditions^ difficulties of operation 
 might develop which would unfavorably influence 
 the results. 
 
 There is one objection which has been raised in 
 the practice of pasteurization in the bottle which 
 may have some weight in certain circumstances. 
 It is claimed that because of the fact that the bot- 
 tles are tightly sealed, there is no chance for the 
 escape of disagreeable or offensive odors. In other 
 heating and cooling processes, a certain amount of 
 aeration takes place, with, as claimed by some 
 dealers, beneficial results. Those who advocate 
 bottle pasteurization claim that during the process 
 of heating, the objectionable gases are driven out 
 of the milk and are forced beneath the bottle cap 
 into the outer air. In so far as known to the 
 writer, the correctness of this claim has not been 
 demonstrated. Neither is it known that objec- 
 tionable odors or flavors have been subjects of 
 
 87 
 
THE PASTEURIZATION OF MILK 
 
 complaint among the users of milk pasteurized in 
 the bottle. 
 
 An objection which may be a serious one at 
 times is this. If the bottle caps are not abso- 
 lutely tight, as may occur when bottle necks are 
 chipped or uneven, there is an opportunity for 
 water to be drawn into the bottle. When the cooling 
 is being carried on there is, of course, a partial 
 vacuum produced in the space above the milk, and 
 if in cooling the bottles are immersed in water, 
 then the water might be drawn into the bottle. If 
 the water were impure the danger becomes ap- 
 parent. 
 
 A certain advantage in the use of the bottle pas- 
 teurizing process from a commercial point of view 
 becomes apparent when only small amounts of 
 milk are to be treated. If individual dairies are 
 compelled by legal requirements to pasteurize the 
 milk sold, it is a comparatively inexpensive mat- 
 ter to equip for pasteurizing in the bottle. The 
 only equipment necessary is a tank large enough 
 to immerse the filled bottles; facilities for supply- 
 ing hot water to the tank, and also for replacing 
 the hot water with cold when the heating is ac- 
 complished. Heat-recording devices are manu- 
 
 88 
 
FROM THE PRACTICAL VIEWPOINT 
 
 f actured for use in connection with bottle pasteuriz- 
 ing. When this method is installed in small dairies 
 there is saved the expense of installing heaters, 
 holders, coolers, pumps and piping. Equally im- 
 portant to the dairyman is the fact that the oper- 
 ating expenses are less, since the amount of ma- 
 chinery to be kept cleaned and in repair is almost 
 nothing. 
 
 A process of pasteurizing which, so far as known 
 to the writer, has been but little employed, con- 
 sists in making use of the vacuum pans which are 
 commonly employed in the manufacture of con- 
 densed milk. With certain changes, these can be 
 used satisfactorily in pasteurizing milk. As usu- 
 ally constructed, these vacuum pans are retort- 
 shaped structures made of copper, and contain at 
 the bottom two or three coils of copper pipe, into 
 which live steam is admitted. When milk is con- 
 densed, these hot pipes raise the milk to the de- 
 sired temperature, and the natural water contained 
 in the milk is drawn off in the form of steam by 
 means of the vacuum pipe attached to the top of 
 the pan. If these pans are used without change 
 as pasteurizing tanks, it is probable that the live 
 steam in the heating coils would have a tendency 
 
 89 
 
THE PASTEURIZATION OF MILK 
 
 to scorch the milk^ and it would be necessary to 
 replace the steam by hot water, which should be 
 rapidly pumped through the coils, the water being 
 maintained at a uniform temperature in tanks out- 
 side the condensing pan. The pans could be used 
 also for holding the milk after it is heated for any 
 desired length of time. 
 
 In plants where seasonal conditions require that 
 the milk be used for different purposes at different 
 times of the year, such an arrangement would 
 effect a saving of expense in equipment, and 
 would thus aid in obtaining greater operating effi- 
 ciency. 
 
 From time to time attempts are made to bring 
 forward some new process for treating milk de- 
 signed to reduce the number of bacteria in milk 
 by some agency other than heat. One of these is 
 the treatment of milk by means of an electric cur- 
 rent. In one electric process, the milk is allowed 
 to flow from chamber to chamber through orifices 
 of small diameter. While so flowing it is sub- 
 jected to a strong alternating current of electricity. 
 It is claimed that this current destroys the bac- 
 teria contained in the milk through the shock to 
 which they are subjected, and that the digestive 
 
 90 
 
FROM THE PRACTICAL VIEWPOINT 
 
 qualities of the milk are not impaired^ but are 
 rather improved. 
 
 It is, however, found necessary to heat the milk 
 to about 130° before subjecting it to the electric 
 current, and during electric treatment it attains a 
 temperature of about 158°, due to the resistance 
 of the milk to the electric discharge. It is an 
 open question whether the destruction of bacterial 
 life, which undoubtedly takes place, is due to the 
 electric current or to the heat to which the milk is 
 subjected. The results of tests made of the milk 
 so treated indicate that the percentage of bacteria 
 destroyed is high. If the effectiveness of the appa- 
 ratus depends upon the heat generated during the 
 process, it is probable the high percentage of bac- 
 terial destruction is partially due to the fact that 
 milk flows in such a small stream through the ma- 
 chine. Every portion of it is thus uniformly 
 heated to the maximum temperature, and even 
 when milk is not held for any appreciable length 
 of time, it has been found in laboratory tests that 
 the bacteria are killed. As before stated, it is a 
 fact that mechanical defects which exist in all ma- 
 chinery render it difficult to maintain uniform tem- 
 peratures. This makes the holding of hot milk a 
 
 91 
 
THE PASTEURIZATION OF MILK 
 
 necessary requirement in order to equalize tem- 
 peratures. 
 
 The ultra-violet rays have been suggested as a 
 means of killing bacteria in milk, Since^ however, 
 these rays have but little penetrating power, it has 
 been found that the opaque character of milk pre- 
 vents obtaining the good results which have re- 
 sulted in the use of the ultra-violet rays in water 
 purification. 
 
 The ozone process, which will by oxidation de- 
 stroy some forms of bacterial life, and which will 
 destroy odors, aLso acts upon the constituent parts 
 of milk and so changes them that it seems probable 
 that ozone can never be satisfactorily substituted 
 for the usual pasteurization process. 
 
 An ingenious idea has been brought to the 
 writer's attention by which it was proposed to de- 
 stroy the bacteria by treatment in vacuum. It is 
 well known that when persons work under abnor- 
 mally high air pressure as in tunnel construction 
 under rivers, etc., it is necessary for them to exer- 
 cise the greatest care in coming out into the normal 
 air pressure. The air, which under pressure is 
 absorbed in the bodily tissues, suddenly expands 
 when the abnormal pressure is relieved. The cells 
 
 92 
 
FROM THE PRACTICAL VIEWPOINT 
 
 of the body may be strained or broken. In such 
 case the disease known as "the bends" results. It 
 has been proposed that a machine might be so con- 
 structed that an abnormal air pressure upon the 
 milk could be suddenly released^ thus allowing the 
 air within the germ bodies to quickly expand and 
 so destroy them. No such system has been made 
 commercially available. 
 
 93 
 
CHAPTER III 
 
 HOLDERS 
 
 As previously stated, the New York City De- 
 partment of Health was the pioneer among health 
 authorities to require that milk, in order to be offi- 
 cially considered to be pasteurized, must be held, 
 after heating for a definite length of time. When 
 this regulation was adopted no holding device was 
 upon the market which was suitable to be used on 
 a commercial basis. Since that time most of the 
 manufacturing firms making milk-handling ma- 
 chinery have constructed and placed upon the mar- 
 ket one or more forms of holding apparatus. These 
 differ in detail, and to a considerable extent in the 
 efficiency with which they operate. In general, 
 however, it may be said they are naturally divided 
 into two classes: 
 
 First, those which may be termed absolute 
 holders, and 
 
 Second, those which are of the continuous or 
 flow type. 
 
 Absolute Holders 
 
 The absolute holders are so called for the rea- 
 son that the milk, after being heated, is all held 
 
 94 
 
FROM THE PRACTICAL VIEWPOINT 
 
 in tanks or compartments for a definite length of 
 time before being discharged. 
 
 The first holder placed upon the market was of 
 this character, and consisted of an upright cylin- 
 drical tank having partitions radiating from the 
 centre, thus dividing the tank into eight compart- 
 ments. Such a holding apparatus is illustrated in 
 Fig. 20. The drawing, however, shows a later 
 type of the same apparatus, in which there are 
 eight separate tanks which are arranged in a cir- 
 cle. An upright shaft extends through the centre 
 of the tank or the group of tanks, as the case 
 may be, to which is attached, at the upper end, a 
 revolving spout, into which the milk is discharged 
 through the pipe from the heater. This spout as 
 it revolves causes each tank to be filled in turn. 
 To each tank is attached at the bottom an outlet 
 pipe and valve. These valves are kept closed by 
 springs, and are opened by means of a revolving 
 arm, or cam, attached to the lower end of the up- 
 right shaft before referred to. These outlet pipes 
 discharge into a common pipe, through which the 
 milk is conveyed to the cooler. By placing the 
 revolving inlet spout in proper position with rela- 
 tion to the revolving cam at the bottom, it can be 
 
 95 
 
THE PASTEURIZATION OF MILK 
 
 readily seen that each tank will be emptied after 
 the milk has been held in the tank during the time 
 required for the shaft to make a complete revolu- 
 tion. By properly gearing the mechanism which 
 operates the shaft it can be seen that the time of 
 holding can be fixed at will for any period de- 
 sired. A little thought, however, will make it clear 
 that the actual holding time will not equal the time 
 required for the shaft to make a complete revolu- 
 tion, since approximately one-eighth of this time 
 is occupied in filling each tank, and one-eighth is 
 required to discharge each tank. In order to ar- 
 rive at the actual minimum time for which we can 
 be sure all the milk is held, we must reduce the 
 time of revolution by one-fourth, or 25 per cent. 
 Thus if it is desired to hold the milk for thirty 
 minutes, it is necessary that the time of revolution 
 of the operating shaft be forty minutes, which 
 reduced by 25 per cent, equals thirty minutes, the 
 actual holding time. 
 
 It is also necessary to make sure that the dis- 
 charge pipes are completely closed before the milk is 
 allowed to enter through the inlet pipe into any tank. 
 Otherwise some milk may pass out of the holder 
 without being held for any definite length of time. 
 
 96 
 
FROM THE PRACTICAL VIEWPOINT 
 
 97 
 
THE PASTEURIZATION OF MILK 
 
 Another point to be observed when partitions 
 separate tlie tanks is to make sure that no tank 
 becomes filled to overflowing. In such case, the 
 milk will flow into a tank from which milk is be- 
 ing discharged, and thus the holding time becomes 
 a matter of great uncertainty. 
 
 In this form of holder considerable foam de- 
 velops, due to the dropping of the milk for a con- 
 siderable distance from the discharge pipe into 
 the body of milk in the tanks. The foamy milk 
 does not retain the heat as well as is desirable, 
 and as a consequence the destruction of the bac- 
 teria is not always sufficiently complete. 
 
 In Fig. 21 the eight compartments or wells are 
 themselves immersed in a tank of water, the tem- 
 perature of which is kept somewhat above that to 
 which the milk is heated. In this form of appa- 
 ratus the tendency to foam is largely overcome 
 from the arrangement which allows the milk to 
 enter the well from the bottom. Both the inlet 
 pipe and the outlet pipe are operated by means of 
 mechanism, which is above the tanks. There are 
 sixteen valves, each of which is made tight by a 
 ground seat, upon which the valve sets. These 
 valves are at the lower end of the plug shanks, 
 
 98 
 
FROM THE PRACTICAL VIEWPOINT 
 
 99 
 
THE PASTEURIZATION OF MILK 
 
 which extend through the milk to the top of the 
 tanks. Any loosening of these valves, or any in- 
 accurate adjustment of the cams which operate 
 them, may cause milk to be discharged from a tank 
 before it has been held a proper length of time. 
 The efficiency of the apparatus would thus be 
 impaired. 
 
 The fact that the temperature of the heated 
 milk is not reduced during the holding process 
 appears to be an advantage. The surrounding 
 jacket of hot water maintains or increases the 
 temperature of the milk in the vats. 
 
 In Fig. 22 the eight tanks are arranged in a 
 circle upon a frame or platform, which itself re- 
 volves, carrying the tanks with it. A central tank, 
 which is stationary, receives the milk from the 
 heater. From this tank the milk is distributed to 
 the various holding tanks by means of pipes, 
 which radiate from a central valve beneath the re- 
 ceiving tank. This single central valve is of very 
 ingenious construction, and is so made that all the 
 holding tanks are filled and are also discharged 
 through the same valve. Thus it is seen that this 
 one valve replaces the sixteen valves which are 
 employed in such an apparatus as shown in Fig. 
 
 100 
 
FROM THE PRACTICAL VIEWPOINT 
 
 101 
 
THE PASTEURIZATION OF MILK 
 
 Fig. 22-B 
 
 21. The chances of valve difficulties are thus 
 reduced. 
 
 The arrangement of this valve is rather diffi- 
 cult to describe. It is shown in Fig. 22-B. A 
 central core is attached to the pipe, which de- 
 scends into it from the central tank. This core 
 remains stationary, and is provided with a sin- 
 gle opening, which is a continuation of and is at 
 right angles to the discharge pipe from the tank 
 
 102 
 
FROM THE PRACTICAL VIEWPOINT 
 
 above it. Outside this core, and closely fitting 
 it, is a shell which revolves around it. Into this 
 shell the eight pipes from the various holding 
 tanks are fastened, and they are so placed that as 
 the shell revolves each pipe is in turn brought op- 
 posite to the opening into the inner core. The 
 milk is thus admitted to the bottom of each hold- 
 ing tank in turn. As the shell continues to re- 
 volve each pipe in the outer shell passes in turn the 
 inner opening and the milk supply is thus shut off 
 from each particular tank, and so remains until the 
 shell has nearly completed its revolution. The pipe 
 opening from the holding tank then comes oppo- 
 site to another opening in the inner core, which 
 extends only a short distance into the core. This 
 opening turns downward and is connected with a 
 pipe, which discharges the milk to the cooler. Thus 
 it is seen that each tank is filled in turn and is in 
 turn discharged automatically. The same method 
 must be employed for arriving at the minimum 
 holding time as that used with the device illus- 
 trated in Fig. 20, namely, the time of revolution 
 must be reduced by 25 per cent. 
 
 The exact holding time may be arrived at in 
 another way, namely, by carefully noting the 
 
 103 
 
THE PASTEURIZATION OF MILK 
 
 exact time at which the last milk enters any sin- 
 gle compartment of the holder, and then observ- 
 ing the exact time at which the first milk flows 
 from the same tank. The difference indicates the 
 minimum holding time. Of course, some of the 
 milk is held for a longer time than that which is 
 thus indicated, but we are sure that none is held 
 for a less time. 
 
 It will be found that the time as observed in 
 this way is nearly equal to that which we obtain 
 by calculation, allowances being made for varia- 
 tions in the mechanical exactness with which the 
 machine operates. 
 
 It will be seen from the illustration that the 
 various holding tanks are insulated by a cork 
 jacket, so that little heat is lost during the hold- 
 ing period. It will be noted, however, that the 
 pipes leading from the holding tanks to the cen- 
 tral valve are not insulated, and in this condition 
 the milk which lies in these pipes during the time 
 of revolution may, and probably will, become 
 cooled, and the effectiveness of the bacterial de- 
 struction will be impaired. This having been 
 brought to the attention of the manufacturers, they 
 provided insulating jackets for the pipes as well 
 
 104. 
 
FROM THE PRACTICAL VIEWPOINT 
 
 as for the tanks. Discharge pipes constructed with 
 these insulating jackets are now provided for ma- 
 chines which are placed upon the market at the 
 present time. 
 
 A modification of this type of holder is now be- 
 ing manufactured in which the holding tanks do 
 not revolve but are made stationary and, instead, the 
 central valve revolves. The same effect is secured 
 as in the other type, and there is this advantage, 
 that less power is required, and the heavy frame 
 required to hold the revolving tanks is not neces- 
 sary. There is also this added advantage, namely, 
 that a small plant may install such an apparatus 
 with but two or four tanks, and as business ex- 
 pands there may be added other tanks, it being 
 only necessary to change the shell of the valve 
 which revolves about the core. 
 
 In Fig. 28 there are seven oblong enamel-lined 
 tanks which are immersed in a tank of hot water. 
 These are each filled in turn by means of valves 
 in a pipe which extends along the upper side of 
 the series. These valves are opened and closed 
 by means of an automatic arrangement operated 
 by a revolving shaft extending parallel to the inlet 
 pipe. A similar shaft extends along the discharge 
 
 105 
 
THE PASTEURIZATION OF MILK 
 
 pipe at the bottom of the series, and operates 
 valves which automatically regulate the discharge 
 of the milk. 
 
 There is one thing which should be carefully ob- 
 served regarding this form of holder. It will be 
 noted that the two shafts which operate both the 
 inlet valves and the outlet valves are impelled by 
 a single worm-driven gear. Thus both shafts 
 move in unison. Care must be taken to make sure 
 that no inlet valve is opened into any tank till the 
 outlet valve is completely closed, otherwise some 
 milk will flow out without being held for the 
 proper length of time. 
 
 In calculating the holding time with this appa- 
 ratus, it must be noted that since there are but 
 seven tanks in the series, there is required one- 
 seventh of the entire period of sequence for each 
 tank to fill and one-seventh for it to be emptied. 
 Thus the entire time of sequence must be reduced 
 by two-sevenths. A little thought will make it 
 clear that as the number of tanks in a series de- 
 creases in number, the time of revolution or se- 
 quence must be increased. With eight tanks a 
 period of revolution of forty minutes reduced by 
 25 per cent, would equal thirty minutes. If, how- 
 
 106 
 
FROM THE PRACTICAL VIEWPOINT 
 
 ©I 
 
 107 
 
THE PASTEURIZATION OF MILK 
 
 ever, a seven-tank holder has a forty-minute se- 
 quence, which is reduced by two-sevenths, we have 
 a holding time of but twenty-eight and four- 
 sevenths minutes, and so on as the number of 
 tanks decreases. 
 
 A modification of the valve system, shown in 
 Fig. 23, is now provided by the manufacturers of 
 this machine. A valve exactly similar in principle 
 to that shown in Fig. 22-B is made use of. All 
 tanks fill and empty from the bottom, thus avoid- 
 ing foam and reduring the danger of by-passing 
 the milk. 
 
 All the types of holders already described are 
 being used with very satisfactory results. To 
 summarize the points which should be observed 
 in either buying or supervising the operation of 
 holders of this character: 
 
 First. — Any serious loss of heat should be pre- 
 vented by complete insulation of all tanks and 
 pipes in which the heated milk is held. Of 
 these insulations, the hot-water jacket is the most 
 expensive and perhaps the best. There is a 
 question whether the added expense secures 
 enough added efficiency to render the expenditure 
 wise. 
 
 108 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Second. — We should be sure that every particle 
 of milk is held for the minimum time required. 
 
 Third. — The valves for admitting and releasing 
 the milk must be so tightly fitted that no milk 
 can by any possibility be discharged before the 
 proper holding time is completed. It may be pos- 
 sible for valves to become so worn by use that 
 annular grooves will be worn around them, thus 
 allowing milk to be by-passed while the valve is 
 closed. 
 
 Fourth. — Make proper calculation to determine 
 that the cycle of filling, holding and emptying of 
 the tanks is long enough to make sure that the hold- 
 ing time is sufficient and in addition to allow for 
 the filling and emptying of the tanks. 
 
 Fifth. — Make sure that the inlet valve is never 
 open into a tank before the outlet pipe is closed. 
 
 Sixth. — Since the ease and convenience of clean- 
 ing is an item of importance, as a general propo- 
 sition it may be said that, other things being equal, 
 a machine which has the fewest pipes and valves 
 consistent with efficient operation is the most de- 
 sirable. 
 
 Seventh. — It is desirable that as little foam as 
 possible be produced in the operation of a holder. 
 
 109 
 
THE PASTEURIZATION OF MILK 
 
 Whatever form of tank holder is used, it is nec- 
 essary that it be thoroughly sterilized before use 
 each day, by the admission of live steam for a 
 considerable period of time. This sterilization is 
 of importance not alone for the destruction of the 
 bacteria contained in it, but also in order that the 
 pipes and tanks may become thoroughly heated im- 
 mediately before use. If they are not so heated, 
 it will be found that the milk first admitted to the 
 apparatus will be considerably cooled, and will be 
 discharged at a temperature much below that re- 
 quired by the regulations, and will so continue until 
 the hot milk has itself slowly heated the appa- 
 ratus. This may require fifteen or twenty minutes. 
 It will be found under such circumstances that the 
 milk first discharged from a holder contains many 
 more bacteria than that which flows from it after 
 the machine is heated. 
 
 Another form of holder which belongs to the ab- 
 solute type is that which is represented by the tank 
 heaters shown in Figs. 11, 12, 13, 14, 14.-B, 15, 1 6, 
 and previously described. In these the milk, after 
 having been heated, is allowed to remain for any 
 desired length of time, and is then released. This 
 method of holding has produced very satisfactory 
 
 110 
 
FROM THE PRACTICAL VIEWPOINT 
 
 results. It has this advantage; that the milk 
 comes in contact with no new metal or apparatus 
 between the completion of the heating process and 
 the time when the milk is cooled. One disadvan- 
 tage is that since it requires considerable time for 
 a large tank full of milk to be discharged^ the last 
 milk leaving the tank is held for a period consid- 
 erably longer than that which first flows from it, 
 and this long holding tends to interfere with the 
 proper rising of the cream. 
 
 Continuous Holders 
 
 The continuous or flow type holders differ from 
 the absolute holders in that the milk, instead of 
 being quietly held in retainers for a definite length 
 of time until the required period for holding is 
 completed, is simply retarded in its flow. This 
 period of retardation is so extended that before the 
 milk passes to the cooler it has retained its tem- 
 perature for the length of time desired. 
 
 There are several forms of continuous holders. 
 One of the first of these is the so-called Park 
 holder, invented by Dr. William H. Park, of the 
 New York City Department of Health, and pat- 
 Ill 
 
THE PASTEURIZATION OF MILK 
 
 Fig. 24 
 
 ented and given to the milk trade for use by the 
 inventor. It is shown in Fig. 24^ and consists 
 primarily of an upright cylindrical tank, into 
 
 112 
 
FROM THE PRACTICAL VIEWPOINT 
 
 which the milk flows at the top, and from which 
 it is discharged at the bottom. An inverted goose- 
 neck attached to the outlet pipe so directs the out- 
 flow that no milk can be discharged until the tank 
 has become filled. In theory, the hot milk which 
 enters at the top becomes gradually cooled as it 
 flows downward, and so the last milk to enter the 
 tank will be the last milk to leave it. If this 
 were entirely true, then the time required for fill- 
 ing a tank would be identical with the holding 
 time. In such case the various particles of milk 
 would pass through the tank like a flock of sheep, 
 one after another. Unfortunately, there are several 
 disturbing elements which enter into the problem, 
 and the particles of milk, instead of resembling 
 sheep, more nearly resemble a flock of chickens 
 in their behavior. In the first place, the milk 
 which is nearest to the outside circumference of 
 the tank becomes cooled more than that which is 
 in the centre, and as it cools it increases in weight, 
 and naturally falls to the bottom and goes out. 
 This tendency is partly overcome by providing in- 
 sulating jackets. In some cases, as in Fig. 25, 
 the jacket is a hot-water covering contained in 
 the space between the inner and the outer shell. 
 
 113 
 
THE PASTEURIZATION OF MILK 
 
 Again, it can be seen that if the temperature of 
 the milk as it enters the tank from the heater is 
 not accurately controlled, it will frequently occur 
 that the temperature will drop, and this cooler milk 
 will fall through the body of milk toward the bot- 
 tom. It is also true that the force of the milk as 
 it enters the tank from the heater will, unless this 
 force is broken, tend to carry the milk deeply into 
 the body of that already in the tank, and so cre- 
 ate currents which will interfere with the actual 
 holding time. This force is broken by placing 
 some sort of a baffle plate under the inlet pipe. 
 This baffle is sometimes so arranged that it floats 
 on the surface of the milk, and rises as the tank 
 becomes filled. In other cases a flat piece of 
 metal is placed near the top of the tank, and may 
 or may not contain perforations which allow the 
 milk to flow through as well as over the edge of 
 the plate. It is immaterial what form of spreader 
 is used so long as the currents are broken up. It 
 will be seen by referring to the illustration that 
 the inverted U-shaped pipe for the discharge of 
 the milk is provided with a by-pass valve, so that 
 the tank can be emptied when the operation is 
 completed for the day. It is important that this 
 
 114 
 
FROM THE PRACTICAL VIEWPOINT 
 
 U-pipe be provided with a vent at the upper end, 
 otherwise a syphon will be created and the milk 
 will all be rapidly drained from the tank. 
 
 In plants where a large amount of milk is pas- 
 teurized, and there is therefore a rapid flow, it is 
 necessary to install more than one of these tanks 
 in series, and in some instances three and four 
 tanks are so installed, each succeeding tank being 
 a little lower than the one before it, and the valves 
 so arranged that the milk-flow is from one to the 
 other through the entire series. This also helps 
 to equalize any uneven temperature which may oc- 
 cur as the milk is discharged into the first tank. 
 
 With all these precautions to insure a steady 
 and even flow, it is never safe to assume that the 
 holding time is correct unless a test is made. Only 
 two feasable means of so testing the tanks have 
 developed. One is the color test and the other 
 the temperature test. Neither are absolutely ac- 
 curate, but are sufficiently so for practical pur- 
 poses. 
 
 In the color test, the tanks are filled with water, 
 heated to the same temperature as is the case when 
 milk is pasteurized. The time of filling having 
 been observed, a solution of some intense color, 
 
 115 
 
THE PASTEURIZATION OF MILK 
 
 preferably methylene blue or uranin^ is allowed 
 to flow into the tank with the heated water. The 
 time is observed between the time of its introduc- 
 tion and the time when the first trace of it appears 
 at the outlet. In order to make the test as ac- 
 curate as possible, care should be taken that a com- 
 plete solution is made of the color, otherwise small 
 particles of solid color may fall through the liquid 
 and deceive the observer. The solution of any 
 color is of course slightly heavier than the liquid 
 in which it is dissolved, and the tendency is for 
 it to fall after its introduction. Therefore, the 
 solution should be made as nearly as possible of 
 the same specific gravity as the water in the tank. 
 If it can be made slightly less in weight than the 
 water the result of the test will be rather better. 
 Even with the greatest care, it seldom happens that 
 two tests of the same apparatus will bring iden- 
 tical results. Unless the speed of flow is accu- 
 rately gauged, the results will differ. 
 
 The temperature test is sometimes used to de- 
 termine the efficiency of these holders. When this 
 method of testing is employed it is the practice to 
 fill the holders with water in the same manner as 
 with the color test. The temperature of the water 
 
 116 
 
FROM THE PRACTICAL VIEWPOINT 
 
 as it leaves the heater is then suddenly raised 
 5° to 10°, and the time at which the rise takes 
 place is noted. A careful watch is then kept at the 
 outlet of the holder to determine when any rise in 
 temperature occurs at this point. The elapsed time 
 indicates the time of holding. The temperature, 
 instead of being raised, may be lowered a given 
 amount at the heater, and the corresponding drop 
 in temperature at the outlet noted. 
 
 The inaccuracy of this method of testing is due 
 to the fact that during the long holding period 
 there is a natural tendency for the changed tem- 
 perature to become diffused throughout the sur- 
 rounding liquid. It can also be seen that when 
 the temperature is raised the natural tendency is 
 for the hotter liquid to remain on top of the tank, 
 while if the temperature is dropped, the tendency 
 is for the cooler liquid to settle toward the bot- 
 tom of the tank. A graphic chart can be made 
 showing the result of these tests very clearly. 
 Using the upright gradations of the chart to indi- 
 cate changes in temperature, and the horizontal 
 gradations to indicate periods of time, the sudden 
 rise at the heater will be clearly shown by an al- 
 most perpendicular line. The line showing the 
 
 117 
 
THE PASTEURIZATION OF MILK 
 
 rise of temperture at the outlet will be compara- 
 tively gradual in its rise and will not reach its 
 highest point for a considerable time. It will also 
 be found that the proportional rise in temperature 
 at the outlet will not be as great as at the inlet 
 of the holder. When the temperature of the inlet 
 is dropped instead of being raised, it will be found 
 that the change of temperature at the outlet occurs 
 in a much shorter space of time. 
 
 In choosing between the color test and the tem- 
 perature test, it can safely be said that for the 
 Park holder the color test is the more accurate. 
 When the tubular holder is used, which will be de- 
 scribed later, it is probable that the two tests are 
 nearly equal in accurac}^ 
 
 When two or more tanks are employed in series, 
 it is desirable that the piping be so arranged that 
 the lowest tank can be filled with milk first when 
 the process of pasteurizing is commenced for the 
 day, and then when the lower tank is full the up- 
 per tanks should be filled and the process contin- 
 ued in this manner. The milk will then flow 
 through all the tanks in succession from the high- 
 est to the lowest. The reason for filling the lower 
 tank first is as follows: When each tank is first 
 
 118 
 
FROM THE PRACTICAL VIEWPOINT 
 
 filled, the milk of course falls from the inlet pipe 
 at the top to the bottom of the tank, and afterward 
 onto the surface of the body of milk in the tank as 
 it fills up to the level of the outlet pipe. In conse- 
 quence there is considerable agitation of the liquid 
 and currents are created. This may cause the last 
 milk which enters the tank to be the first to be 
 discharged, and our holding time becomes a mat- 
 ter of uncertainty. If, however, the lower tank is 
 the first one filled, we are then sure that all the 
 milk in this tank is held for at least the time re- 
 quired for the other tanks to fill. 
 
 This method of filling may be effected in either 
 of two ways: First, a pipe may extend along the 
 top of the tanks in such a way that by opening the 
 proper valves the milk may be directed into either 
 tank at will. Second, the pipe may be arranged 
 at the bottom of the series in such a way that 
 either tank may be filled, if the proper valves are 
 opened and closed. Both arrangements of pipes 
 are shown in Fig. 24. 
 
 It has been found by tests that this form of 
 holder never holds the milk for a period of time 
 as long as that which is required for them to be 
 filled. Depending upon the form of the tanks and 
 
 119 
 
THE PASTEURIZATION OF MILK 
 
 the method of construction, the percentage of hold- 
 ing time to filling time is from 25 per cent, to 70 
 per cent. It is usual to estimate the time as 60 per 
 cent, of the filling time. It is true that tanks which 
 are tall and of comparatively narrow diameter are 
 more efficient than are short and wide tanks, the 
 reason probably being that with long, narrow tanks 
 the movement of milk is comparatively rapid, and 
 there is less diffusion of the milk than when the 
 movement is slow, as in the wide, short tank. Tests 
 have been made which indicate that when the rate 
 of flow is twelve feet or over a minute, there is 
 very little diffusion of the liquid. 
 
 In all tanks of this character it is desirable, and 
 indeed almost a necessity, that some sort of an 
 insulating jacket be provided in order that there 
 be as little loss of temperature as possible during 
 the holding process. The reason for this, as be- 
 fore stated, is that the cooling of the milk which 
 is near the outer circumference of the tank causes 
 downward currents. Thus the milk which falls 
 to the bottom on account of these currents is car- 
 ried out of the tank before it has been held for the 
 proper length of time. 
 
 The insulation may be provided by means of 
 
 120 
 
FROM THE PRACTICAL VIEWPOINT 
 
 jackets of asbestos, cork or felt, or a surround- 
 ing tank of water may be provided, as in Fig. 25. 
 By means of the insulation, if properly applied, 
 the heat will be retained and the milk as it flows 
 from the tank will have a temperature but little 
 below that at which it enters. When the hot water 
 insulation is used, as in Fig. 25, the initial tem- 
 perature of the milk may become somewhat in- 
 creased during the holding period. This addi- 
 tional heating, it can be seen, has a tendency 
 to cause the milk which may enter the tank below 
 the average temperature to become heated and rise 
 toward the top of the tank, thus increasing the 
 time for which it is held. As a matter of fact, the 
 water-insulated tanks have shown a good percent- 
 age of holding time as compared with the filling 
 time when the color test has been applied. The 
 test of their efficiency as measured by the destruc- 
 tion of the bacteria contained in the milk is also 
 good. 
 
 This Park type of holding tank has been some- 
 what modified by various manufacturers in this re- 
 spect, namely, by introducing the milk at the bot- 
 tom and allowing it to flow out at the top instead 
 by the reverse method of flow. When the inlet 
 
 121 
 
THE PASTEURIZATION OF MILK 
 
 pipe from the heater enters the tank at the centre 
 of the bottom, and the milk is forced upward till 
 the tank is filled, the color tests made have indi- 
 cated that their efficiency percentage was small. 
 Especially was this true when the outlet pipe was 
 at one side and near the top of the tank. It can 
 be seen that the force which is necessary to impel 
 the milk in at the bottom against the weight of 
 the superimposed milk in the tanks must of neces- 
 sity create currents. This will be more noticeable 
 if the milk is forced through the heater by means 
 of a pump. The impulses will create a somewhat 
 uneven flow and the resulting currents will be 
 greater. The discharge of the milk from one side 
 of the top also tends to cause currents and an 
 uneven overflow. 
 
 One manufacturer has so constructed his tanks 
 that the inlet pipe enters at the top through the 
 cover, is carried down through the body of the 
 milk in the tank to the bottom, and then dis- 
 charges the milk into the tank by means of an 
 enlarged perforated foot somewhat resembling a 
 sprinkler head on a watering can. In the plants 
 where this apparatus is used the milk flows by grav- 
 ity and there are thus no pump impulses. The 
 
 122 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Fig. 25 
 
 force is broken up by the descent of the milk 
 through the body of that in the tank. It can be 
 seen that when the milk as it enters the tank is be- 
 low the average temperature, the tendency will be 
 
 123 
 
THE PASTEURIZATION OF MILK 
 
 for it to remain at the bottom, and so be heated 
 before it is discharged. In this holder, also, the 
 outflow is from the top, but the flowage into the 
 discharge pipe is from many points at the surface 
 into a gathering pan. In this way surface cur- 
 rents are avoided. 
 
 One of the disadvantages of the upright tank 
 holder is that when it is of large size it is rather 
 difficult to clean. It becomes necessary for the 
 workmen to get inside the tank in order to thor- 
 oughly clean it. Some upright tanks are being 
 made which are mounted upon trunions in such a 
 way that when the pipes are disconnected the tank 
 may be turned into a horizontal position, and the 
 cleaning can then be more easily performed. 
 
 A second form of continuous or flow type tank 
 is so constructed that a long horizontal tank, which 
 opens at the top, is divided by cross partitions into 
 several compartments. At the top of each of these 
 partitions is a gathering trough, extending along 
 the upper edge of the partition. A tube attached 
 to the centre of this trough extends to near the 
 bottom of the next succeeding compartment. This 
 is shown in Fig. 26. 
 
 In operation, the milk enters into the compart- 
 
 124 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Fig. 26 
 
 merit at one end of the tank, and when the com- 
 partment is full, the milk flows into the gathering 
 trough and is carried by means of the tube to the 
 bottom of the succeeding compartment. Here the 
 same routine is repeated till all the compartments 
 are full. Then the flow becomes continuous till 
 all the milk is pasteurized. When all the milk has 
 left the heater, of course the flow from the holder 
 stops. The tanks are at this time all full, and 
 it is then necessary to remove the plug which is 
 
 125 
 
THE PASTEURIZATION OF MILK 
 
 near the bottom of each compartment in turn 
 till all are emptied. Since these plugs are re- 
 moved by hand^ it is necessary to place the hand 
 and arm into the empty compartment at each 
 operation. The danger of contamination is thus 
 evident. 
 
 When the partitions are low it has been found 
 that the milk flows over the tops of all of them, 
 and there is thus but little holding time possible, 
 since the milk flows almost directly from the inlet 
 to the outlet pipe. Even with the best of con- 
 struction, tests have shown that the percentage of 
 holding time to the filling time is small, sometimes 
 being as low as 10 per cent, to 15 per cent. 
 
 The third form of continuous flow type holder 
 now used quite extensively is shown in Fig. 27. It 
 consists of a series of large-size tubes arranged in 
 a box- like structure. These tubes are connected 
 one with another at the ends by suitable hinged 
 heads, so that the milk which enters the top tube 
 of the series flows forward and backward through 
 all of them and is discharged from the lower tube. 
 The discharge pipe is carried upward in the form 
 of an inverted U tube in a similar manner to that 
 shown in Fig. 24. This gives assurance that no 
 
 126 
 
FROM THE PRACTICAL VIEWPOINT 
 
 127 
 
THE PASTEURIZATION OF MILK 
 
 milk will be discharged until all the tubes have 
 become filled. 
 
 In this form of holder, the flow of milk through 
 the apparatus is comparatively rapid. As before 
 stated, this rapid flow tends to prevenjt diffusion, 
 and the holding time more nearly approaches the 
 time required to fill the apparatus than in any 
 other form of flow-type holder. In some respects 
 it is rather difficult to make a satisfactory color 
 test upon this holder on account of the fact that 
 the air, which of course fills the holder when the 
 filling with milk is commenced, is not all forced 
 out as completely as is desired, and thus air pock- 
 ets are formed. It thus occurs that some milk is 
 forced from the discharge tube before the appara- 
 tus is completely filled. Thus it is difficult to ob- 
 tain the exact time required to fill the tubes. It 
 is claimed by the manufacturers that when it is 
 operating under the most favorable conditions the 
 milk will be held for 98 per cent, of the time re- 
 quired for the apparatus to become filled. The 
 tests observed by the writer indicate that the hold- 
 ing time is from 80 per cent, to 90 per cent, of the 
 filling time, which is a greater percentage than 
 with other holders. 
 
 128 
 
FROM THE PRACTICAL VIEWPOINT 
 
 The same difficulty which is experienced in 
 emptying the tubular heater is observed with rela- 
 tion to the tubular holder. This is due to the very 
 slight inclination or pitch of the tubes from the 
 horizontal. In some cases it has been the prac- 
 tice to force the last milk out of the tubes by fol- 
 lowing it with water. The possibility of adul- 
 terating the milk unless great care is exercised is 
 apparent. In the later machines made, the tubes 
 are given a greater pitch, and the objection due to 
 slow drainage is at least reduced. 
 
 It should be noted that unless the tubes are very 
 thoroughly heated by means of hot water or steam 
 immediately before use, the first milk entering the 
 holder will be so cooled that its temperature at the 
 discharge will be below that which is required. 
 
 This form of holder can be easily cleaned, since 
 the tubes are large, and can be readily opened. 
 It is thus easy to force a suitable brush through 
 the pipes, and it is not difficult to see if all dirt 
 has been removed. It is of course necessary that 
 the cleaning be performed with great thorough- 
 ness in order that it be effective in the destruction 
 of bacteria. 
 
 Whatever form of holder is used, whether it be 
 
 129 
 
THE PASTEURIZATION OF MILK 
 
 of the absolute or the continuous type, careful 
 sterilization should be practised, not only directly 
 after the apparatus is washed each day, but also 
 immediately before its use on the following day. 
 The reason for this is due to the fact that any 
 organic matter which may remain in the apparatus 
 after wasliing may contain spores of bacteria 
 which are not readily killed by the heating to 
 which the apparatus is usually subjected. These 
 spores may develop into active bacteria during the 
 time that the apparatus remains idle. Especially 
 would this be true if, as usually occurs, consid- 
 erable moisture is allowed to remain in the machine. 
 For this reason the holder should be thoroughly 
 sterilized before use each day. It may here be 
 noted that there is even a greater necessity for 
 sterilizing the cooler, pipes, bottling machine, etc., 
 with which the pasteurized milk comes in contact 
 after leaving the holder. Any recontamination at 
 these points is not afterward corrected and may 
 be a source of danger. 
 
 It should here be noted that a feature which 
 has been introduced into some milk plants con- 
 sists in a brief superheating of the milk after it 
 leaves the holder. This is accomplished by allow- 
 
 130 
 
FROM THE PRACTICAL VIEWPOINT 
 
 ing the milk to flow in a thin layer over pipes 
 which are heated to about l62° to l65°. The milk 
 is then immediately cooled. It is claimed that bac- 
 teria which are resistant to 142° temperature are 
 nevertheless considerably weakened by this heat- 
 ing, and are completely destroyed at the brief 
 heating of 162°. It is also claimed that the cream 
 rises in a more satisfactory manner when the ad- 
 ditional heating is employed. The feature of ap- 
 plying a brief superheating temperature to milk 
 already pasteurized has been covered by a patent. 
 
 It must be evident, when a little thought is 
 given to the matter, that in order for any con- 
 tinuous holder to be reliable, the rate of milk flow 
 must be uniform. In very few forms of appara- 
 tus is there any attempt to properly control the 
 rate of flow. When milk flows by gravity, the 
 rate at which it flows into the heater will depend 
 partly upon the volume of the fluid in the tank 
 which feeds the machine. When a pump is used 
 to supply the heater, its rate of delivery may be 
 influenced by the steam pressure, or by the degree 
 to which the steam valve is opened, or by the con- 
 dition of the valves and pistons. In places where 
 a gravity flow is emjiloyed, it is not a difficult mat- 
 
 131 
 
THE PASTEURIZATION OF MILK 
 
 ter to arrange a feed cup which will make it cer- 
 tain that no more than a definite amount of milk 
 can reach the heater per hour. When a pump is 
 used, a float valve in the tank which feeds the 
 heater can be made to shut off the intake pipe to 
 the feed tank. This increases the milk pressure 
 upon the pump and the discharge pipe, and by 
 means of a suitable valve this increased pressure 
 is made to close the steam valve which supplies the 
 pump. This method of controlling the flow of 
 milk to the heater is in successful operation in 
 several pasteurizing plants. 
 
 132 
 
CHAPTER IV 
 
 TEMPERATURE CONTROLLERS AND RECORDERS 
 
 In order that uniformly good results in the pas- 
 teurization of milk may be obtained, it is abso- 
 lutely necessary that the temperature to which the 
 milk is heated be controlled in such a way that 
 there will be no great variation. In order to con- 
 trol this properly, three things are necessary — 
 first, a uniform, even flow of milk; second, a steam 
 pressure which does not vary; and third, that the 
 steam which is admitted to the heater be so con- 
 trolled that whatever variations there may be in 
 the temperature of the inflowing cold milk may be 
 met by varying amounts of steam, admitted to the 
 heater. This control will, of course, also prevent 
 any excessive heating which would follow if too 
 much steam entered the heating apparatus. 
 
 The matter of an even milk flow has been dis- 
 cussed in the previous chapter. 
 
 The control of steam pressure may be accom- 
 plished in various ways. It is, of course, necessary 
 that there be sufficient boiler capacity to insure 
 that the steam pressure does not fall below a cer- 
 
 133 
 
THE PASTEURIZATION OF MILK 
 
 tain minimum amount. One of the simplest meth- 
 ods of steam pressure control is by an instrument 
 constructed like the safety valve of a boiler. A 
 movable weight upon an arm regulates the pressure 
 which is desired. When properly set any increase 
 of pressure above the desired amount lifts the arm 
 and shuts the steam valve connecting with the pipe 
 leading to the heater. Other more complicated 
 forms of apparatus are on the market, the details 
 of which it is not necessary to describe. 
 
 In the matter of the control of the temperature 
 at which the milk leaves the heater, it is, of course, 
 possible to do this by hand. This method makes it 
 necessary that a man constantly watch the ther- 
 mometer attached to the outlet milk pipe, and at 
 the same time open or close the steam valve to ad- 
 just the steam flow to the varying temperature of 
 the milk. 
 
 If the speed of milk flow, and also the steam 
 pressure is well controlled, it is possible for a care- 
 ful workman to regulate the milk temperature with 
 good success. If, however, these factors are con- 
 stantly varying, it is nearly impossible for even a 
 careful man to obtain good results. It is, of course, 
 more economically eflficient to arrange for auto- 
 
 134 
 
FROM THE PRACTICAL VIEWPOINT 
 
 matic temperature control than to depend upon 
 man power, provided, of course, that the machine 
 works as it is intended to work. 
 
 The machines designed to control temperatures 
 are operated in two ways. In one machine the 
 bulb which is inserted into the milk is filled with 
 some volatile liquid like ether and is connected 
 by means of a capillary tube with a pressure coil, 
 which in turn regulates the flow of compressed air 
 to a valve. The compressed air is employed as a 
 motive power to operate the valve which regulates 
 the admission of steam to the milk heater. Such a 
 system involves the installation of an air pump 
 and a tank for the storage of compressed air. To 
 one unfamiliar with the apparatus the description 
 may appear involved and the operation compli- 
 cated. Fig. 28 shows this system. 
 
 In another form of controller, electricity is em- 
 ployed as a motive power in operating the steam 
 valve instead of compressed air. The bulb which 
 enters the milk contains two metals, which are so 
 fastened together that the difference in expan- 
 sion makes and breaks the electrical connection 
 and the steam valve is operated by this means. 
 This is shown in Fig. 29- This method can, of 
 
 135 
 
THE PASTEURIZATION OF MILK 
 
 a. 
 
 > 
 <. 
 
 < 
 
 or 
 o 
 
 CC 
 
 136 
 
FROM THE PRACTICAL VIEWPOINT 
 
 ELECTRICAL CONTROLEFJ 
 
 RCCOROCF}^ 
 
 To 
 PAiTBURlZEft 
 
 Terminal j 
 
 To y^ 
 
 controllino 
 
 Valve 
 
 Tlrminal To 
 The-rmostat 
 
 bcCTION OF 
 
 Pastcurizer 
 
 Fig. 29 
 
 course, be employed only where an electric current 
 is available. This current, however, may be fur- 
 nished by a small inexpensive dynamo, which can 
 be operated at any plant where power is available. 
 Both these forms of control work in a satisfactory 
 manner. Of course, they are somewhat delicate 
 
 137 
 
THE PASTEURIZATION OF MILK 
 
 in adjustment, and careful handling is necessary. 
 Either form will control the milk temperature 
 within 2°, as indicated by the temperature re- 
 corder. 
 
 A method of temperature control which was 
 proposed by the writer some years ago had for its 
 basis a principle which has been made use of 
 in this connection to a limited extent only. This 
 consisted in this, namely, that the temperature of 
 the heating medium be so controlled as to remain 
 constant, and that the milk which flowed out of 
 the heater be kej^t at a uniform temperature by 
 varying the speed of flow of the milk through 
 the heater. This reverses or inverts the present 
 practice, in which the speed of milk flow is con- 
 stant, while the 'temperature of the heating med- 
 ium varies. The proposed method would have 
 this advantage, that no part of the milk could ever 
 be heated higher than the temperature of the water, 
 and if this water temperature were controlled by 
 a thermostat no scorching of the milk would ever 
 result. It is evident that with a uniform heating 
 medium the milk which flows through the heater 
 will take up more of this heat if the speed of flow 
 is slow than it will if the milk moves rapidly over 
 
 138 
 
FROM THE PRACTICAL VIEWPOINT 
 
 tlie heating surface. A thermostat attached to the 
 milk outlet pipe from the heater could be made 
 to control the steam which supplied the milk 
 pump. This would vary the speed of milk flow. 
 If milk flows by gravity to the heater, the ther- 
 mostat might be made to open or close a valve in 
 the feed pipe. 
 
 The nearest approach to the use of this prin- 
 ciple occurs in some plants when the heated water 
 is kept at a uniform temperature by a thermostat, 
 and the milk flow is also constant. The heating 
 surface of the heater is so very large compared to 
 the amount of milk heated, that the water is never 
 more than 3° or 4° hotter than the milk, and 
 there is therefore no possibility of scorching the 
 milk. In these plants also the efficiency of the re- 
 generative principle is carried as near the theo- 
 retical limit of perfection as it seems possible. The 
 water leaving the heater is within a few degrees of 
 the temperature of the cold milk entering the ma- 
 chine. This cooled water is conveyed to the milk 
 cooler, where it is used for cooling the hot milk. 
 It becomes so heated when leaving the cooler that 
 it is but a few degrees lower than the hot milk. 
 It can be seen that but little steam is required to 
 
 139 
 
THE PASTEURIZATION OF MILK 
 
 again raise the temperature to the desired point. 
 The increased amount of heating and cooling sur- 
 faces required for this form of pasteurizing ma- 
 chine calls for careful cleaning and sterilization. 
 
 Automatic Recorders 
 
 The automatic recording of the milk temperature 
 is desirable, and in most cities where the pas- 
 teurization of milk is subject to public control it 
 is required. The milk company which is really 
 anxious to put out a safe product wants an office 
 record which will indicate whether the work is 
 being properly performed. With health authori- 
 ties, such a record is necessary, since it is impos- 
 sible for inspectors to be at pasteurizing plants all 
 of the time to watch their operations. A correct 
 automatically made record is the best substitute 
 for personal inspection. To be of ideal value, such 
 a record should show, not only the temperature, but 
 also the time of holding. When the tank or batch 
 heater is used, the single recorder attached to the 
 tank will show these items with fair accuracy, but 
 the observer must note whether or not the cooling 
 is either wholly or partially done in the tank itself. 
 
 140 
 
FROM THE PRACTICAL VIEWPOINT 
 
 If such cooling in the tank does take place, then 
 the length of time for which the recording mark 
 remains at the highest point is a correct indica- 
 tion of the time for which the hot milk is held. 
 If the cooling is performed entirely outside the 
 holding tank, then allowance must be made for the 
 time necessary for the milk as drawn from the 
 tank to fall below the point where the thermome- 
 ter bulb is inserted into the milk. It is plain that 
 the making of the record by the recorder pen will 
 continue as long as the bulb remains in the hot 
 milk. Thus, if the highest temperature were re- 
 corded for forty-five minutes, and it required twen- 
 ty-five minutes for the milk in its discharge to fall 
 below the recorder bulb, then the actual holding 
 time for all of the milk would be but twenty 
 minutes. 
 
 When the continuous holding process is used, it 
 is desirable that a recorder be attached to the out- 
 let of the heater, and that another be placed in the 
 outlet pipe from the holder. If the charts on these 
 two recorders are both set at the correct hour of 
 the day then it is easy to calculate the duration 
 between the time of the first discharge of hot milk 
 from the heater and the first discharge from the 
 
 141 
 
THE PASTEURIZATION OF MILK 
 
 holder. If one recorder only is in use^ it is more 
 important that it be placed at the holder outlet. 
 It is evident that if there is a serious loss of heat 
 during the holding process due either to imper- 
 fect insulation or to insufficient preliminary heating 
 of the holder, then the milk would not be satisfac- 
 torily pasteurized, since some of the dangerous 
 organisms originally in the milk may escape de- 
 struction. The holder recorder indicates this. 
 
 The various recording instruments upon the 
 market differ in this one particular, namely, that 
 in one form ether, or a similar volatile fluid, is 
 used in the thermometer bulb and capillary tube, 
 while in the other, the bulb and tube are filled with 
 mercury. One of the former is shown in Fig. 30, 
 while the mercury bulb is shown in Fig. 31. There 
 is a variation also in the method employed for 
 regulating the recording arm. In a form of re- 
 corder not shown, another form of adjusting screw 
 is attached to the recording arm, and an improved 
 device is used for securing the paper chart to the 
 face of the instrument. 
 
 In the selection of a recording instrument, one 
 of the most important points to consider is its sen- 
 sitiveness to rapid or frequent changes in tempera- 
 
 142 
 
FROM THE PRACTICAL VIEWPOINT 
 
 •'ink. ^ 
 
 IS*"' 
 58| 
 
 •J ^ a a - " "^ 
 
 o 
 
 CO 
 
 I 
 
 !^ 111 
 
 V vy "? 3 i 
 
 '^ -C: .V t o o o 
 
 t c a -^ S .\ H: 
 
 2 S S c 6' 5 S 
 
 "i CQQ g ^ :J O 
 
 
 143 
 
THE PASTEURIZATION OF MILK 
 
 Fig. 31 
 
 ture. If it is slow in responding to such changes, 
 there is a possibility that there may be a wide 
 fluctuation of temperature, which will not be shown 
 upon the recording chart. The manufacturer of 
 each instrument claims that his machine is very 
 sensitive to rapid temperature changes. 
 
 It should be borne in mind that a temperature 
 
 144< 
 
FROM THE PRACTICAL VIEWPOINT 
 
 recorder is in reality a pressure recorder only in 
 which the changes in pressure due to varying tem- 
 peratures are so graduated as to indicate with 
 fair accuracy the temperature of the milk. With 
 the ether instrument, the amount of movement of 
 the arm for, say, a ten degree rise, changes as the 
 higher temperatures are reached. So the grad- 
 uations on the chart are not of the same width all 
 the way across. In the mercury instruments this 
 is not true, but the degree graduation lines are 
 equally distant one from the other. There are cer- 
 tain inaccuracies in these instruments which must 
 be taken into account. Thus it can be seen that 
 the temperature of the room in which the recorder 
 is placed must have an effect upon the pressure 
 coil. In the instrument shown in Fig. 30 an at- 
 tempt is made to correct this by attaching to the 
 arm a compensating coil. This coil also contains 
 mercury, and is so placed that it moves in a di- 
 rection opposite to that of the coil to which the 
 capillary tube is connected. The recording arm 
 is attached to both coils. When, therefore, both 
 coils move as the result of the room temperature, 
 no effect is produced upon the recording arm, but 
 it remains stationary. Any increased pressure in 
 
 145 
 
THE PASTEURIZATION OF MILK 
 
 one due to the temperature of the heated milk will 
 move the pen and cause it to make a proper rec- 
 ord. The same effect may be produced in another 
 way. In this case the comjDensating coil is con- 
 structed of two different metals, and the differences 
 in expansion cause it to move, but in a direction 
 opposite to that produced by the ether coil. 
 
 It must also be borne in mind that the recorder 
 does not register absolute temperatures, but only 
 relative changes in temperature. Thus inaccurate 
 adjustment of the arm may produce a record which 
 is deceptive. For this reason it is necessary to 
 provide some means of adjusting the arm in order 
 to secure an accurate reading. In some instru- 
 ments the arm has a flexible joint which can be 
 moved by hand. This is rather difficult to accom- 
 plish, without danger of breaking the recording 
 arm, and fine adjustment is not easy. There is 
 also the danger that the joint will be uninten- 
 tionally moved when placing the chart upon the 
 face of the dial. 
 
 In one recorder a post is so placed that it can 
 be turned by means of a clock key. After the 
 proper adjustment has been made, the post may be 
 held in proper position by sealing it to other rigid 
 
 146 
 
FROM THE PRACTICAL VIEWPOINT 
 
 posts beside it. This form is of value to the in- 
 spector, since by placing his seal upon it he can 
 be sure that no change is made in the recorder 
 during his absence. 
 
 In other instruments other means of adjustment 
 are provided. If, as in some forms, the coil is so 
 placed that its axis of rotation is the same as that 
 of the recording arm, then no movement of the arm 
 at the joint can affect the relative temperature 
 valves of the varying degree spaces upon the chart. 
 With this form there appears also to be less lia- 
 bility to vibrate with the vibration of the walls of 
 the buiding in which it is placed. This form also 
 has the advantage that the knob or screw which 
 holds the chart to the face of the dial is so ar- 
 ranged that the chart cannot be left loose upon the 
 apparatus, but must either be securely fastened 
 or left off the instrument altogether. It is also 
 very easy to fasten the chart to the clock face. 
 
 It has frequently been found by inspectors that 
 instruments were not accurately adjusted. This 
 may be due to a defect in the instrument itself, or 
 it may be due to an intentional false adjustment 
 by the man who is operating the pasteurizer. He 
 may wish to indicate upon the chart a higher tem- 
 
 147 
 
THE PASTEURIZATION OF MILK 
 
 perature than is actually employed in the pas- 
 teurization of the milk. For this reason those in- 
 struments whose adjustment is under the control 
 of the inspector alone are desirable. They should 
 be frequently tested. This frequent checking is of 
 advantage to the honest milk dealer as well^ since 
 if a recorder by any means shows a temperature 
 lower than it should^ there may be trouble with 
 the cream line due to an unsuspected high tem- 
 perature in the pasteurizer. 
 
 Health authorities must be alert in watching the 
 temperature records which are kept on file by the 
 dealer. It is, of course, possible for a dishonest 
 dealer to make false records. These may be made 
 in various ways. Instances have been known 
 where the entire record has been made by hand, 
 an ordinary pen being used. This requires more 
 skill than the average dealer possesses, if he is to 
 deceive the wideawake inspector. It is possible 
 to put a chart upon a recorder dial and leave it so 
 loosely attached that it does not revolve with the 
 clock. Then, when the desired temperature is 
 reached, the chart may be turned by hand and a 
 beautiful even line be drawn upon it. When the 
 first milk from a holder has a temperature lower 
 
 148 
 
FROM THE PRACTICAL VIEWPOINT 
 
 than required by law, some dealers wait until the 
 proper temperature is attained, and then, by plac- 
 ing the thermometer bulb in the milk, they get a 
 record which indicates an immediate rise of tem- 
 perature to the highest point, and then a uniformly 
 even line. Any record which indicates that the 
 temperature has been raised at once to the maxi- 
 mum point, and then continues with no variation 
 during the entire run, should be looked upon with 
 suspicion. Inspectors with a little experience soon 
 learn to detect false records, by evidences not al- 
 ways easy to explain, and they are able to gain 
 from dealers the admission of irregularities which 
 are at first denied. 
 
 149 
 
CHAPTER V 
 
 CLEANING AND COOLING THE MILK CLEANING 
 
 CONTAINERS HOME PASTEURIZATION, ETC. 
 
 It is of course needless to say that all milk 
 should be clean when it arrives at the plant where 
 it is to be pasteurized. That is^ there should be no 
 visible dirt in the milk. It is also desirable that 
 all dirt which is not readily detected be absent. 
 While visible dirt and bacteria are not identical, 
 still it is true that visible dirt is almost always ac- 
 companied by bacteria in large numbers. Dealers 
 should therefore make every effort to induce the 
 dairymen to be so cleanly in their methods that 
 very little dirt will find entrance into the milk. 
 The sediment test when properly used is an ex- 
 cellent method of finding out whether or not the 
 dairyman is cleanly in his methods. If, however, 
 the producer is allowed to strain his milk before 
 bringing it to the shipping station, then the sedi- 
 ment test simply tells the dealer whether or not 
 the farmer has strained the dirt out. Or rather, 
 let us say it indicates either that the farmers' 
 methods of caring for the milk are cleanly, or that 
 
 150 
 
FROM THE PRACTICAL VIEWPOINT 
 
 the evidence of his uncleanliness has been strained 
 out. It seems wise to advise dealers to prohibit 
 the straining of milk at the farm. This may 
 seem like radical doctrine, but a little thought dis- 
 closes its wisdom. If the milk is unstrained, then 
 the sediment test becomes of real value to the 
 dealer in directing his attention to those dairymen 
 who need attention from the inspector. Then, 
 again, after the dirt once gains access to the milk, 
 the straining simply removes that part of the dirt 
 which is the least objectionable, namely, the in- 
 soluable part. If milk is poured over a strainer, 
 the dirt remains upon the surface, and the milk 
 which may be afterward poured through the 
 strainer helps to carry through those soluble por- 
 tions which may have at first escaped solution. 
 This soluble portion, of course, contains most of 
 the bacteria. 
 
 The removal of the dirt at the shipping sta- 
 tion or the pasteurizing plant may be accom- 
 plished by straining as it is received, or since the 
 straining of cold milk is difficult, it may be strained 
 while hot from the heater and before it enters the 
 holding apparatus. There is no objection to this, 
 since whatever bacteria are carried through into 
 
 151 
 
THE PASTEURIZATION OF MILK 
 
 the holder are destroyed during the holding 
 process. 
 
 Clarification 
 
 The centrifugal clarifier is used to a large ex- 
 tent^ and removes not only the dirt which is ordi- 
 narily seen in milk, but also the pus cells, blood 
 cells, etc., which usually escape detection. The 
 clarifier, as is well known, is made in a manner 
 similar to a separator, the difference being that 
 the cream is not separated from the milk, but the 
 dirt, pus, etc., is thrown against the outer por- 
 tions of the revolving shell, and is there collected. 
 Of course, this material contains a great many bac- 
 teria, which are carried along with the heavier ma- 
 terial. Tests, however, made by the plating 
 method, do not show the great decrease in the 
 number of bacteria which might be expected, and 
 in many instances the apparent number is in- 
 creased. This is probably due to the fact that the 
 clumps of bacteria are broken up and so produce 
 more colonies upon the plate than results when 
 they remain bunched together in the original milk. 
 One of the clarifiers is illustrated in Fig. 32. 
 
 One objection to the clarifier has been the 
 
 152 
 
FROM THE PRACTICAL VIEWPOINT 
 
THE PASTEURIZATION OF MILK 
 
 tendency which there was to create foam^ espe- 
 cially if the milk were cold. This foaming is due^ 
 of course_, to the entrance of air into the milk dur- 
 ing the process. Milk which has been previously 
 pumped seems more likely to foam than when 
 pumps have not been used. Machines are now 
 made by which the air is excluded, and no foam, 
 or almost none, is produced when they are oper- 
 ated, even when the milk is cold. It is generally 
 held that the clarification of milk by a centrifugal 
 machine is a good thing. It is claimed that the 
 pus cells, leucocytes, etc., which are in the milk, 
 tend to form a covering for the bacteria contained 
 in the milk, to such an extent that they are some- 
 what protected and are not so readily destroyed 
 by heat. It is claimed that the removal of this 
 covering by means of the clarifier therefore assists 
 in the complete destruction of the bacteria. This 
 claim has not been fully demonstrated to the knowl- 
 edge of the writer. 
 
 It is the practice of some dealers to strain the 
 pasteuried milk as it enters the bottling machine. 
 This is to be condemned unless the strainer is 
 completely covered and is sterilized at the same 
 time that the final sterilizing of the bottler occurs. 
 
 154 
 
FROM THE PRACTICAL VIEWPOINT 
 
 In fact_, any straining after the milk leaves the 
 holding apparatus is undesirable, and seems to be 
 useless if the milk has been well cleaned before 
 pasteurizing. 
 
 Coolers 
 
 The rapid cooling of heated milk has been held 
 to be an important factor in the satisfactory pas- 
 teurizing of milk. It was claimed that the sud- 
 den chilling had a destructive effect upon the bac- 
 teria_, which had been already weakened by the 
 heating. Investigations made by Ayers and John- 
 son, however, seem to indicate that when the cool- 
 ing is accomplished, during a period of two hours, 
 there is no noticeable increase in bacterial growth. 
 
 There are three general types of milk coolers 
 in use: 
 
 First; The open cooler or aerator. This consists 
 of a series of tubes, made usually of copper and 
 well tinned. These tubes are arranged one above 
 another, and are so connected at the ends that cold 
 water or brine is forced through the entire series. 
 The water flow is into the lower tubes and up- 
 ward through the series, so that the coldest water 
 comes in contact with the coldest milk. This form 
 
 155 
 
THE PASTEURIZATION OF MILK 
 
 Fig. 33 
 
 of cooler is shown in Fig. 33. The cooler is usu- 
 ally arranged in sections. Through the upper 
 section cold water, frequently well water, flows, 
 while the lower section contains ice water or brine. 
 This form of cooler is very effective in rapidly 
 
 156 
 
FROM THE PRACTICAL VIEWPOINT 
 
 cooling the milk when it is made large enough to 
 take care of the milk which is to be treated. They 
 are made by various manufacturers in forms which 
 vary somewhat in details. Some are so arranged that 
 the regenerative principle is made use of. In most 
 of these the hot milk from the holder is allowed 
 to flow over pipes through which the incoming 
 cold milk flows. This is a means of saving heat 
 units, but such coolers are rather difficult to clean, 
 and there is a danger that the pressure of the cold 
 milk on the inside of the pipes will find openings 
 through which the milk will be forced into the pas- 
 teurized milk on the outside. The contamination 
 which results is not corrected by repasteurization. 
 Some one may say that the same danger exists when 
 the cooling medium on the inside of the pipes is 
 water. This is true, but it must be remembered 
 that the water pipes do not need to be taken apart 
 for cleaning, while the milk pipes must of neces- 
 sity be opened for cleaning daily, and the danger 
 from loosened joints is therefore greater. 
 
 Another objection which has been urged to the 
 use of the open cooler is that the milk is exposed 
 to the air, and that there is great danger from 
 air contamination. This is true when the air is 
 
 157 
 
THE PASTEURIZATION OF MILK 
 
 full of dust or foul odors. In most milk plants^ 
 however, the air is so moist that little dust is flying 
 about, and recent investigations by Ruehle and 
 Kulp * of milk contamination by stable air indi- 
 cate that even under unfavorable conditions the air 
 contamination is not as serious a matter as we have 
 supposed. Of course, milk coolers can be en- 
 closed by tightly fitting metal covers, or they may 
 be located in separate rooms or compartments, and 
 so be protected from contact with air which is 
 questionable. If a separate room is provided, 
 suitable ventilation should be secured for carrying 
 off steam, and the opening for the admission of air 
 should be so protected that the incoming air will 
 be filtered. 
 
 Since it is difficult to clean and sterilize metal 
 covers for coolers, it seems more desirable that the 
 milk be protected by enclosure in separate rooms. 
 
 The complete sterilization of this open type of 
 cooler is a rather difficult matter. The reason for 
 this is that the cooling surface cannot be subjected 
 to the action of steam under pressure. The usual 
 method employed is to direct live steam from a 
 
 *BuI. 409. N. Y. Agricul. Exp. Sta. 
 
 158 
 
FROM THE PRACTICAL VIEWPOINT 
 
 hose against the outer surface of the pipes, after 
 the washing has been completed. It is well known 
 that steam when relieved of its pressure rapidly 
 cools, and a person can hold his hand a short 
 distance from an open steam pipe with no incon- 
 venience. It often happens that not all the parts 
 of the cooler receive the benefit of even this re- 
 duced temperature. The tubes, of course, must 
 be empty of the water usually contained in them 
 before they are steamed. 
 
 It might be feasible to provide covers for these 
 coolers which would be sufficiently tight to allow 
 the pressure of the steam to be retained to some 
 extent before it escaped into the outer air. Some 
 covers are now made which are fairly tight. 
 
 The best way to sterilize this form of cooler is 
 to have the tubes of sufficient strength so that 
 steam may be admitted on the inside under pres- 
 sure. In such case the sterilization is from the 
 inside. If, while the pipes are hot from the en- 
 closed steam, water is allowed to trickle over the 
 outside, this is heated, and is itself converted into 
 steam, which helps to cleanse the pipes. 
 
 Care should be taken to be assured that the 
 steam which rises from the milk while being cooled 
 
 159 
 
THE PASTEURIZATION OF MILK 
 
 does not become condensed upon any unclean sur- 
 face, such as the ceiling or a metal covering over 
 the cooler, and from thence fall back into the milk. 
 If this occurs, very serious contamination may 
 result. 
 
 Open pipe coolers should not be made very long 
 in relation to their height. It can be seen that 
 the water flowing through long pipes will become 
 warmed on the inner surface of the tubes, while 
 the central more rapidly flowing core may still be 
 cool. More ejffective cooling is obtained where this 
 milk flow is broken up by frequent turns as the 
 water is returned from one pipe to another. 
 
 Second: The cooling may be accomplished in 
 the same apparatus in which the milk is heated 
 and held. This can be done when the tank sys- 
 tem of pasteurization is employed, as illustrated in 
 Figs. 12, 13, 14, 1 i-B, 15, 16. When cooling is so 
 carried on, the cold water or brine takes the place 
 of the hot water in the pipes, by means of which 
 the heating was originally done. It is found in 
 practice that when the same coil is used for the 
 brine as well as for the hot water, there is dan- 
 ger that careless workmen may allow the brine and 
 the water to become mixed. There is therefore a 
 
 160 
 
FROM THE PRACTICAL VIEWPOINT 
 
 loss of brine. Some heating tanks are now made 
 with double coils^ one of which is used for heating 
 and the other for cooling. If the cooling is done 
 in tank pasteurizers there is the advantage that 
 the milk comes in contact with no additional metal 
 surface or other material after it is placed in the 
 tank till it is drawn into the final containers. 
 
 The principal objection to the tank cooling is 
 that usually a long time is required to reach the 
 desired low temperature. As stated in the chap- 
 ter on heaters, the time is frequently from an hour 
 to an hour and a half. Large coils and a rapid 
 circulation of brine will decrease this cooling time 
 greatly. 
 
 In country plants at a distance from the point 
 of milk consumption, the time of cooling is an im- 
 portant consideration from the dealers' point of 
 view, since the time between the receipt of the milk 
 from the farmer and the departure of the milk 
 train is limited. 
 
 The change in temperature from the high heat 
 necessary to pasteurize the milk to the cold re- 
 quired for rapid cooling produces a considerable 
 strain upon the pipes of the coils, and the joints 
 are apt to become weakened. 
 
 161 
 
THE PASTEURIZATION OF MILK 
 
 Third: The tubular cooler is being used to a 
 considerable extent. In this form of cooler the 
 pipes through which the hot milk flow are en- 
 closed by other pipes^ through which cold water 
 is forced in a direction opposite to the flow of 
 the milk. These coolers are exactly similar to 
 the tubular heaters illustrated in Figs. 7, 10, 
 and 11. 
 
 This form of cooler is effective and rapid; it has 
 this advantage, that sterilization by steam under 
 pressure can be made complete. There is the same 
 difficulty in emptying the tubes which was noted 
 in describing the tubular heater and holder, and 
 whatever advantage there may be in exposing milk 
 to the air in order to get rid of bad odors, etc., is 
 absent from the tubular cooler. 
 
 The regenerative principle is made use of in the 
 tubular heater and cooler, as already described, 
 and there is little danger of the milk becoming 
 contaminated by leakage of the water, since the 
 joints of the water pipes do not come in contact 
 with the joints of the milk jDipes. 
 
 One of the most efficient forms of apparatus to 
 use from the point of view of economy of heat 
 units is probably that shown in Fig. 11. The 
 
 162 
 
FROM THE PRACTICAL VIEWPOINT 
 
 great amount of piping, however, renders it diffi- 
 cult to keep clean. 
 
 Washing of Containers 
 
 It is of course important that containers in 
 which pasteurized milk is placed shall be thor- 
 oughly cleaned and sterilized. There can be little 
 advantage gained in the proper pasteurization of 
 milk if it is to be immediately placed in contain- 
 ers which are not free from all dangerous bacteria. 
 The relative importance which the cleaning of cans 
 and bottles has in the bacterial content of milk 
 has not been recognized to the extent which it 
 deserves. 
 
 Cracks and open seams, especially in milk cans, 
 may harbor particles of milk which are heavily in- 
 fected with bacteria, which in many cases are of a 
 type which are difficult to destroy by ordinary 
 methods. Especially is this true if the cans or 
 covers contain moisture, since this aids in the de- 
 velopment of the bacterial life. 
 
 It is undoubtedly true that the methods em- 
 ployed in washing bottles are generally much more 
 satisfactory than those in use in handling the cans 
 and covers. Bottle-washing machines of various 
 
 163 
 
THE PASTEURIZATION OF MILK 
 
 makes are on the market which perform excellent 
 work. Some of these employ revolving brushes, 
 which are automatically forced into the bottles, in 
 which a strong washing solution has been placed. 
 In others, the cleaning is accomplished by inject- 
 ing under high pressure jets of washing solution 
 into the inverted bottles. This type of machine is 
 that which is in the most general use at the pres- 
 ent time. 
 
 As usually constructed, this washing apparatus 
 is a long machine, in which are placed several 
 tanks for containing the washing and rinsing 
 fluids. One tank contains a strong washing solu- 
 tion, another contains water for the first rinsing, 
 and a third contains clean water for the final rinse. 
 Over these tanks are placed plates having a sur- 
 face area of about the same size as that of the top 
 of a bottle case. These plates are perforated, and 
 powerful pumps force the liquid in the tanks 
 through these perforated plates in such a way that 
 the liquid is forced upward into the bottles, which 
 are inverted in cases over them. An automatic 
 feed pushes the cases from plate to plate along a 
 track made for the purpose. The bottles thus get 
 first a cleaning with the fairly hot washing solu- 
 
 164 
 
FROM THE PRACTICAL VIEWPOINT 
 
 tion, then a rinsing with hot water, after which 
 clean water is forced into them, which is near the 
 boiling temperature, and sometimes a final jet of 
 live steam is forced into the bottles. If the final 
 rinse water is clean and hot, and the steam is ap- 
 plied long enough, the bottles leave the machine 
 at a temperature of from 150° to 170°, and are 
 reasonably free from bacteria. 
 
 Several points are to be borne in mind in using 
 a machine of this kind. In the first place, no ma- 
 chine can be depended upon to fully clean an 
 extremely dirty bottle, particularly those which are 
 returned from the bottle exchanges and the dumps. 
 Such bottles should first be washed by hand upon 
 revolving brushes, where they can be clearly seen 
 by the workman. They should then be washed again 
 in the regular jet- washing machine. Another im- 
 portant point is that the perforations in the wash- 
 ing plates are liable to become clogged either with 
 particles of dirt, or with rust, or it may be with 
 deposits which are thrown down from water which 
 is very hard. If these openings are stopped up 
 it will mean that some bottles are not washed as 
 it is intended they should be, and dealers may be 
 unable to account for an unusually large number 
 
 165 
 
THE PASTEURIZATION OF MILK 
 
 of dirty bottles which they find from time to time 
 upon their routes. 
 
 Another important item is the temperature of 
 the rinsing water. Unless this temperature is con- 
 trolled by a thermostat, it may be easy to care- 
 lessly let the temperature drop below the steriliz- 
 ing point. Workmen who have to take away the 
 washed bottles from the machine and store them 
 find that it is uncomfortable to handle bottles which 
 are extremely hot, and these men may, therefore, 
 allow the steam supply to the rinsing tank to be 
 cut down to such an extent that the bottles do not 
 get sterilized. A thermostat attached to this 
 rinsing tank will automatically keep the tempera- 
 ture up to the desired point. If, in addition to 
 this, a temperature recorder is also attached to this 
 tank, a record will be kept which a dealer may 
 keep on file as an office record. This will enable 
 him to keep in closer touch with the work which 
 is being done in his washing-room. 
 
 Another important matter is to make sure that 
 the water which is used for the final rinse water 
 is fresh, clean water, and that it is not used over 
 and over in the final rinse tank. Most of the 
 newer machines are so arranged that the water 
 
 166 
 
FROM THE PRACTICAL VIEWPOINT 
 
 which is forced into the bottles for the final rinse, 
 instead of falling back into the tank from which 
 it is pumped_, is carried back into the tank behind 
 it. From here it can be properly used for the pre- 
 liminary rinsing of the bottles. The use of fresh, 
 clean water for final rinsing is somewhat expen- 
 sive when a public water supply is used, and also 
 a good deal of steam is required to heat it, but in 
 order to obtain sterile bottles it is necessary. For 
 heating this water use can be made of the exhaust 
 steam from engines and pumps, and thus heating 
 expenses may be cut down. 
 
 There is one form of automatic washing ma- 
 chine in which the bottles which are being treated 
 are forced down into successive tanks of water, and 
 the inverted bottles are pushed over fingers from 
 which water is forced in a direction somewhat 
 tangent to and also at right angles to the inserted 
 finger. The water as it is forced into the bottle 
 has therefore somewhat of a scouring action. This 
 is of advantage in removing dirt which has ad- 
 'hered to the glass. In this machine, also, the 
 water which is used for the final rinse is heated 
 under pressure, and as a result, when it is forced 
 into the bottle, its temperature is frequently above 
 
 167 
 
THE PASTEURIZATION OF MILK 
 
 the boiling point. One feature of this machine 
 is unique. The machine is so constructed that, 
 when the final rinse water falls below a definite 
 temperature, of say 180°, it refuses to operate, 
 since the bottles will not be lifted from the rinse 
 tank, but will remain submerged. The machine 
 thus becomes its own thermostat. This effect is pro- 
 duced in the following manner: The platform 
 upon which the cases are placed, and by means of 
 which they are lowered into and lifted from the 
 rinsing tank, is so counterbalanced that when the 
 bottles are full of water the weight is too great 
 for the case to be lifted. If the water which is 
 forced into the bottles is hot enough so that as re- 
 leased from pressure it is converted into steam, 
 then the water is forced out of the bottles, and they 
 have sufficient buoyancy to enable the counter- 
 weight to lift the entire case out of the tank. 
 
 The older method used in washing bottles, even 
 when large quantities were handled, was to pro- 
 vide means for soaking the dirty bottles, then to 
 wash them by hand on revolving brushes, and 
 finally to sterilize them in separate rooms, or in 
 tanks into which live steam was discharged for a 
 considerable time. This method is still in use to 
 
 168 
 
FROM THE PRACTICAL VIEWPOINT 
 
 a considerable extent and is effective, but is more 
 expensive than the machine method. This added 
 expense is principally due to the amount of labor 
 involved in the many handlings of the bottles 
 which is necessary. Various soaking machines are 
 in use. Some of them are so arranged that it is 
 not necessary for the workmen to put their hands 
 into the soaking solution, since an endless con- 
 veyor carries the bottles into and out of the soak- 
 ing tank. The solution is made so strong that all 
 foreign matter, even the bottle caps, is disinte- 
 grated. After being removed from the soaker, a 
 rinsing by means of a machine which forces hot 
 water into them renders them sterile. 
 
 Some method of thorough hand washing with 
 subsequent careful sterilizing probably gives bet- 
 ter results than does machine work, provided the 
 men who do the washing are careful to see that no 
 dirty bottles get by them. This is an expensive 
 method of cleaning bottles. 
 
 Whatever method of washing is employed, care- 
 ful attention should be given to proper inspection 
 of the washed bottles. Probably no one thing can 
 do more harm to a milkman's business than for his 
 customers to frequently find bottles which have 
 
 169 
 
THE PASTEURIZATION OF MILK 
 
 dirt adhering to the inside of them. Even though 
 the dirt may have been sterilized by the steam 
 treatment and be therefore harmless, the custom- 
 er's sense of cleanliness is offended and the dealer 
 may lose his trade. 
 
 A practice which has been adopted by some 
 dealers commends itself to the careful milkman. 
 This is the practice of restirilizing the bottles after 
 they have been inspected and all dirty ones re- 
 moved. Any contamination which may have re- 
 sulted from the handling of the bottles by the 
 workmen will thus be remedied. 
 
 After treatment, washed bottles should be stored 
 either in an inverted position until they are used, 
 or else they should be protected by suitable cov- 
 ers or by placing them in separate rooms where no 
 infection can occur. If a cold-storage room is 
 provided, for the washed bottles, there is a cer- 
 tain advantage. When it is remembered that the 
 mass of glass in a milk bottle nearly equals the 
 mass of the milk contained in it, it can be seen 
 that if the bottle is warm, before it is filled, the 
 temperature of the milk will be raised to a con- 
 siderable extent. When empty bottles are stored 
 at room temperature in the summer, they may 
 
 170 
 
FROM THE PRACTICAL VIEWPOINT 
 
 have a temperature of 65° to 70° when the milk 
 goes into them. If milk is cooled by the cooler 
 no lower than 50°, it will, by coming in contact 
 with the warm bottle, be warmed to a temperature 
 of from 55° to 60°. Bacteria troubles may fol- 
 low, especially if the cases of bottled milk are not 
 immediately iced, or if they are placed in a cold 
 room without ice being placed in contact with the 
 bottles. 
 
 It is a known fact that milk either in cans or 
 bottles will be very slow in cooling if the con- 
 tainers are placed in dry air, even though the tem- 
 perature of the air is considerably below that of 
 the milk. Milk containers, however, which have 
 ice placed upon them, will become cooled in a short 
 time. 
 
 Dealers and others have not realized to what an 
 extent unclean cans and covers may, and in fact 
 do, ajffect the bacterial content of the milk. Un- 
 til comparatively recently, no effective can wash- 
 ing, sterilizing and drying machines have been 
 placed on the market, and even now comparatively 
 few milk dealers are using them to the extent to 
 which their merit entitles them. It is usually found 
 that in milk-handling plants, both in those where 
 
 171 
 
THE PASTEURIZATION OF MILK 
 
 the milk is pasteurized and in those from which the 
 milk is shipped in the raw state^ the sterilizing is 
 very inadequately done. Usually the cans are 
 washed by hand with a brush, and are then placed 
 over a single jet of rinsing water and then over a 
 single jet of live steam. The time occupied in 
 both rinsing and steaming is usually but a few 
 seconds. It often happens that the can covers are 
 not steamed at all_, but are simply rinsed in water 
 which is not over clean. When the cans which 
 are to be returned to the patrons are washed, the 
 steaming which the cans receive is so brief that it 
 is almost negligible. This is not altogether the 
 fault of the man who is washing the cans, for 
 when milk is being delivered rapidly to the plant 
 there is little time for long steaming. As a matter 
 of fact, the cans require a more careful cleansing 
 and sterilizing than do the bottles, since they are 
 more likely to contain crevices and uneven sur- 
 faces than are the bottles. If for any reason it is 
 not feasible for a dealer to install an automatic 
 can washer, it is still possible to obtain satisfac- 
 tory results. An apparatus which is comparatively 
 inexpensive may be constructed by providing a long 
 table or runway of iron plate on which there are 
 
 172 
 
FROM THE PRACTICAL VIEWPOINT 
 
 installed two or three jets of water for rinsing cans, 
 and also three or more jets of steam. Each jet 
 should be provided with an automatic valve which 
 will be opened by the weight or pressure of the 
 can as it is placed over the jet. If flanges of iron 
 or sections of gas pipe are so attached to the table 
 that they will engage the flare of the can mouth 
 as it is inverted over the table, it will be impos- 
 sible to remove the can until it has travelled entire 
 length of the table and has thus received the 
 influx of water and steam from each of the jets. 
 It is possible to so arrange the table that both 
 cans and covers will be treated at the same time on 
 the same table. This is accomplished by install- 
 ing two sets of gas-pipe guides, one of them to 
 hold the cans in place and the other of them to be 
 just above the covers as they are pushed along the 
 table, with the open end down. The cans referred 
 to in this connection are the standard forty-quart 
 cans used most largely in the East. 
 
 Various machines are on the market which are 
 so arranged that the cans, after having been well 
 steamed, are also dried by means of a blast of 
 heated air. This drying is important for two 
 reasons. First, because the moisture which may 
 
 173 
 
THE PASTEURIZATION OF MILK 
 
 be left in the can renders the condition favorable 
 for the growth of bacteria which have escaped de- 
 struction, and second, because cans which are not 
 dry are much more likely to become rusty. Rusty 
 cans are hard to clean, and frequently become a 
 loss to the owner because they soon wear out and 
 are discarded. One form of can rinser, steamer 
 and dryer is rather ingeniously arranged. The ex- 
 haust steam, after having been used to operate a 
 turbine-driven fan, is employed to sterilize the 
 cans. The steam pipe which supplies the fan tur- 
 bine passes in coils through an air chamber, and 
 thus is used to heat the air which is forced by the 
 fan into the cans after they have been sterilized. 
 There is thus a very economical use of the steam, 
 and the apparatus is also very compact. 
 
 Cans, after they have been treated, should be 
 stored in an inverted position until they are used 
 for containing milk. If, however, they are thor- 
 oughly dry, there seems to be no objection if the 
 covers are tightly placed upon them and they are 
 then stored without inverting. 
 
 In determining what test to apply in order to 
 ascertain whether or not milk containers are ster- 
 ile, or sufficiently so for practical purposes, it 
 
 174 
 
FROM THE PRACTICAL VIEWPOINT 
 
 should be remembered that we are not dealing 
 with laboratory conditions, and that therefore ab- 
 solute sterility is not necessary, however desirable 
 it may be from a theoretical standpoint. Our milk 
 itself is not sterile, and if we can be assured that 
 the containers are sufficiently clean so that they 
 will not add any appreciable amount of bacteria to 
 the milk, and that those which may be added are 
 not of a pathogenic character, then health authori- 
 ties should be satisfied. Remembering that a quart 
 of milk contains about one liter of fluid, or 1,000 
 cubic centimeters, it seems reasonable to allow the 
 washed bottles to contain 1,000 bacteria. This 
 would add but one bacterium to each c.c. of milk 
 contained in the filled bottle. In like manner, 
 40,000 bacteria in a washed can might add the 
 same amount of bacterial contamination to the 
 forty quarts of milk contained in the filled can. 
 If none of these were of the coli group, it is proba- 
 ble that no danger would result. As a matter of 
 fact, with methods of cleansing which may be easily 
 secured, the bacterial content of the containers will 
 be much less than the allowable amount above re- 
 ferred to. 
 
 175 
 
THE PASTEURIZATION OF MILK 
 
 Bottle-Filling 
 
 The filling of the bottles is more an economic 
 problem than a sanitary one. Of course, the care- 
 ful cleaning and sterilization of the apparatus is 
 necessary, no matter what kind of filler is used. 
 Any failure in this respect may cause the milk to 
 gather up bacteria while it passes through the 
 bottling machine. This may cause annoyance, at 
 least, when tests are made which indicate a high 
 bacterial content. If, however, the cleaning is 
 carefully done, the items which most interest the 
 milk men are the questions of expense and of effi- 
 ciency in operation. 
 
 If a machine is operated by hand power, there 
 is the question whether human power is cheaper 
 than machine power. If automatically operated 
 by outside power, either electric, steam or hydrau- 
 lic, then the matter of bottle breakage, case dam- 
 age, and loss of milk from broken bottles is an 
 important consideration. A power-driven machine 
 may or may not be slower in operation than hand 
 power. The conditions surrounding each plant 
 must be considered and decisions made in accord- 
 ance with them. 
 
 176 
 
FROM THE PRACTICAL VIEWPOINT 
 
 The rotary filler and capper is coming into quite 
 extensive use, with many features about it which 
 appeal strongly to the milkman. 
 
 Bottle-Capping 
 
 It is important that milk, after having been 
 pasteurized, shall not be recontaminated in any 
 way. If containers are properly cleaned, the great- 
 est danger of such reinfection lies in the practice 
 of capping bottles by hand. When this method of 
 capping is employed, the caps are frequently kept 
 in open boxes beside the bottling machine, and they 
 are sometimes kept in the pockets of the workmen 
 who are capping the bottles. There is thus con- 
 stant danger that the caps will become infected by 
 dust in the air, by milk which is spattered upon 
 them or by means of the hands of the persons who 
 handle them. Men who handle bottle cases and at 
 the same time work about machinery cannot easily 
 keep the hands clean. The milk caps then suffer. 
 If any germs of disease are about these employees 
 then the danger becomes apparent. 
 
 Some form of capping machine is desirable. Sev- 
 eral such are on the market, and many of them 
 
 177 
 
THE PASTEURIZATION OF MILK 
 
 are doing satisfactory work. It is not necessary to 
 describe the characteristics of each. Those are 
 most desirable which fulfil the following conditions : 
 
 First: The caps used should be stored in sterile 
 containers or tubes before they are inserted in the 
 machine. 
 
 Second: A very small percentage of the bottles 
 should be missed in capping. 
 
 Third: They should be so constructed that they 
 can be readily taken apart for cleaning, and they 
 should have no concealed pockets or spaces where 
 milk is likely to collect and become sour or decom- 
 posed. 
 
 Fourth : They should be strongly constructed in 
 order that they may stand without breakage or dis- 
 arrangement, the rather rough usage to which they 
 are subjected. 
 
 It is very desirable that milk bottles be sealed 
 after they are filled. By sealing is meant that 
 they be so protected that they cannot be opened 
 without the fact being readily detected by the con- 
 sumer. The desirability of this sealing process 
 gets its force from two reasons: 
 
 First: To prevent the drivers or others from 
 opening the bottles and adulterating the milk. 
 
 178 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Instances have been known where the drivers of 
 rival companies have opened the bottles belonging 
 to their competitors, and have fouled the milk in 
 order to cast discredit upon the milk delivered by 
 the rival concern. Other drivers have taken cream 
 from the tops of bottles, and have filled the bot- 
 tles with water. The cream they have sold for 
 their own profit. Bottles which were effectively 
 sealed could not be treated in this way. 
 
 Second : To prevent possible contamination of the 
 milk by means which are unintentional. The use of 
 the usual paper plug cap leaves a space above the 
 cap where dust and dirt and ice water from melt- 
 ing ice, etc., can collect. Unless this is carefully 
 washed off before the bottle is opened, it is likely 
 to fall into the milk. If a bottle of milk which 
 when filled has a temperature of say 50° to 55° 
 is then placed in a case and covered with ice, the 
 milk is cooled to perhaps S5° to 40°. This causes 
 the milk to contract. The air in the space above 
 the milk also contracts, and a suction is thus cre- 
 ated. The water which collects on the top of the 
 cap is then drawn into the bottle around the edge 
 of the cap, taking with it some of the dirt which 
 may have collected there. 
 
 179 
 
THE PASTEURIZATION OF MILK 
 
 The drivers of retail delivery wagons who han- 
 dle the reins, care for the horses and then in de- 
 livering milk grasp the bottles by the neck, are 
 particularly likely to leave some dirt or contami- 
 nating material upon the lips of the bottles over 
 which the milk will be poured. Serious infection 
 may result. Caps which are real seals and which 
 at the same time protect the neck and lips are on 
 the market, but are rather expensive. They are 
 used by dealers upon special grades of milk, such 
 as Certified, Grade A, etc., but are as yet too costly 
 to be used upon the lower or common grade of 
 market milk. A great many attempts have been 
 made to devise a safe seal which shall be protec- 
 tive and shall be inexpensive, but none have been 
 very successful. A fortune awaits the man who 
 can produce a satisfactory seal of this character. 
 
 Paper Bottles 
 
 For fifteen years or more various sorts of paper 
 milk bottles have been upon the market. They 
 have been made in various forms. Some were 
 made of pulp which was formed into the shape of 
 an ordinary bottle. Some have been crimped into 
 
 180 
 
FROM THE PRACTICAL VIEWPOINT 
 
 a bottle form from a single sheet of heavy paper. 
 Others have been made of heavy waxed paper, 
 through which the cream was visible. Some have 
 had straight parallel sides. They have been made 
 round and square; have been filled from the top, 
 and have been filled from the bottom, but the suc- 
 cess which has attended them has not been very 
 marked, especially in the East. There are some 
 firms in the western part of the country where 
 their use has been rather extensive and where they 
 are said to be satisfactory. 
 
 The objections to their use has been — 1st, the 
 expense. They are more costly than are glass 
 bottles, when it is considered that the glass bottle 
 is used repeatedly, while the paper one is used 
 but once. 
 
 2nd. Many of them are not strong enough to 
 endure the heavy icing and rough handling to 
 which they are subjected. 
 
 3rd. Customers have been accustomed to seeing 
 the cream in the bottle, and object to bottles where 
 the cream is out of sight. 
 
 4th. The constantly increasing cost of paper 
 renders it questionable whether the equipment for 
 using paper bottles may not prove to be available 
 
 181 
 
THE PASTEURIZATION OF MILK 
 
 for a short time only, and its expense thus 
 wasted. 
 
 5th. There is always uncertainty concerning the 
 cleanliness of the bottles as delivered by the manu- 
 facturers for use, and also as to whether or not 
 the material used in the paper may affect the milk. 
 
 There are undoubted advantages in the use of 
 the paper container, among which are: 
 
 1st. That the expense of handling and trans- 
 portation will be lessened, on account of the lesser 
 weight of the paper. 
 
 2nd. The expense of washing returned bottles 
 will be saved, since the paper container will be 
 used but once. 
 
 3rd. The possible danger which exists through 
 the return of bottles from the public dumps, and 
 from houses in which there are communicable dis- 
 eases will be lessened if the single service container 
 is used. 
 
 4th. The danger from broken glass, which occa- 
 sionally finds its way into the milk, will be ob- 
 viated, and the wounds which are inflicted by 
 broken bottles upon workmen who handle and wash 
 them will be prevented. 
 
 182 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Home Pasteurization 
 
 Many physicians who thoroughly believe that 
 milk should be pasteurized for infant feedings also 
 recommend that this pasteurization be performed 
 in the home, and that the pasteurized milk be 
 fed as quickly as possible after the heating is 
 completed. This method eliminates the possibil- 
 ity of recontamination which may occur when milk 
 is handled under commercial conditions, and it also 
 insures that those bacteria which are not destroyed 
 during the pasteurization process will have little 
 opportunity for growth and increase between the 
 pasteurization of the milk and its consumption. 
 
 It is not the purpose of the writer to here de- 
 scribe the various methods employed for home pas- 
 teurization. Such information may be obtained 
 from the pamphlets which are distributed by those 
 responsible for maintaining the various infant-feed- 
 ing stations located in our cities. Some of these 
 stations are maintained by the municipalities and 
 some by private individuals. Dr. Rosenau, in his 
 book on "The Milk Question/' discusses this phase 
 of pasteurization quite fully. 
 
 Whatever method of home treatment is employed, 
 
 183 
 
THE PASTEURIZATION OF MILK 
 
 care should be taken that the heat is high enough 
 and is maintained for a sufficient time to reach all 
 parts of the milk, and so kill the pathogenic bac- 
 teria. The heating medium should not be hot 
 enough to cook or change the chemical characteris- 
 tics of the milk or to impart to it a disagreeable 
 odor or taste. 
 
 184 
 
CHAPTER VI 
 
 EFFICIENCY OF VARIOUS APPARATUS 
 
 During the writer's experience in the actual 
 operation of pasteurizing plants, a great many sam- 
 ples of milk have been taken which have been ex- 
 amined for their bacterial content in order to de- 
 termine the efficiency of the various pasteurizing 
 plants in the destruction of bacteria. These results 
 have been tabulated, showing the bacterial content 
 before, during and after pasteurization. In these 
 tables the kind of apparatus are indicated by fig- 
 ures only, no name of apparatus or of the manu- 
 facturers being given. The dealers at whose plants 
 the tests were made are indicated as "A," "B," 
 "C," etc. Thus at a plant operated by dealer 
 "A," for instance, a heater illustrated by Fig. 00, 
 a holder like Fig. 00, and a cooler like Fig. 00 may 
 have been employed. 
 
 Lest the reader be misled as to the efficiency 
 of certain definite forms of apparatus, and lest cer- 
 tain manufacturers be led to feel that results ob- 
 tained have failed to give justice to the apparatus 
 
 185 
 
THE PASTEURIZATION OF MILK 
 
 handled by them, the reader is warned that effi- 
 ciency tests are sometimes misleading. It should 
 be remembered that at least four factors enter into 
 the causes which produce the effects indicated. 
 
 1st. The character of the apparatus itself. 
 
 2nd. The carefulness with which the plant is 
 operated by those responsible for it. 
 
 3rd. Whether the apparatus is thoroughly 
 cleaned and sterilized. 
 
 4th. The character of the milk treated. 
 
 It is, of course, understood by all those familiar 
 with bacteriological work that these are factors of 
 error in the results which can never be entirely 
 overcome. 
 
 If apparatus is so constructed that the heating 
 and holding and cooling are true to their indicated 
 capabilities, then the results will be good — if the 
 machine is properly operated and if it is clean. 
 These factors being reliable, the results can be 
 taken at their face value if the milk is of normal 
 quality and does not contain, we will say, certain 
 forms of bacterial life which are difficult to destroy. 
 
 When results are good, it undoubtedly means 
 that both the apparatus and its operation are sat- 
 isfactory. If the results are bad, it is not always 
 
 186 
 
FROM THE PRACTICAL VIEWPOINT 
 
 easy to say whether the machine, its operation, or 
 the milk is at fault. 
 
 In regard to the milk itself, there are many fac- 
 tors which must be taken into account when de- 
 termining the efficiency of any apparatus. Esti- 
 mates of machine efficiency based upon the 
 percentage of bacteria destroyed are frequently 
 misleading. It can be readily seen that if the bac- 
 terial content of the raw milk is high, any good 
 pasteurizer will kill a large percentage of the 
 germs in the milk. For instance, if the original 
 milk contained 5,000,000 bacteria per c.c, and 
 after being pasteurized contains 100,000 bacteria, 
 there would have been a reduction of 98 per cent, 
 of the bacteria in the original milk. Milk contain- 
 ing 100,000 bacteria per c.c. would not, however, 
 be considered to be an entirely satisfactory prod- 
 uct to place upon the market, especially if it con- 
 tained organisms of the coli type. 
 
 Again, let us suppose that the original milk con- 
 tained 10,000 per c.c, and that by means of the 
 pasteurizing process this number was reduced to 
 1,000; such a milk would undoubtedly be a proper 
 milk for consumption, although the percentage of 
 reduction had been 90 per cent only. It is there- 
 
 187 
 
THE PASTEURIZATION OF MILK 
 
 fore plainly seen that the efficiency of pasteuriz- 
 ing machinery, when expressed in percentage re- 
 duction of bacteria only, must be taken with a 
 great deal of reserve. It is necessary to know the 
 character of the raw milk, and also to know if coli 
 types are all destroyed. In speaking of the de- 
 struction of coli, it should be remembered that 
 germs of this group are not necessarily all danger- 
 ous. In this connection they are used as indicators 
 only. It is known that they are more difficult to de- 
 stroy than are any of the pathogenic or disease-pro- 
 ducing bacteria. If, therefore, the coli are all 
 killed, it is safe to assume that no dangerous mi- 
 crobes remain alive. While, if the coli are present 
 in the finished product, there is a possibility that 
 disease germs are also present. It is known pretty 
 definitely that if milk is heated to 142-145° for 
 thirty minutes, all coli will be destroyed. 
 
 The following tables are compiled from very 
 many tests made. When these tests were made 
 there were three or four samples of milk taken at 
 each point of examination; for instance, four sam- 
 ples of raw milk were taken at the same time. 
 When these were examined, the average of all the 
 counts was determined. In the same way there 
 
 188 
 
FROM THE PRACTICAL VIEWPOINT 
 
 were four samples taken at the outlet of the heater, 
 the holder, and so on. In the tables herewith com- 
 piled, only the average counts are indicated, in or- 
 der to avoid any bewildering mass of figures. It 
 should be therefore borne in mind that bacteria 
 counts here indicated are averages. 
 
 In figuring out the percentage of reduction, 
 the relation between the bacterial content of the 
 raw milk and the milk as it leaves the holder is 
 considered. It will frequently be found that the 
 number of bacteria in the milk leaving the cooler 
 is higher than when it leaves the holding appara- 
 tus, and that this number is again increased when 
 the milk enters the bottles and cans. Usually un- 
 clean coolers, bottling machines and bottles are 
 responsible for this increase. 
 
 Not all of the types of apparatus which are 
 illustrated and described in this book have been 
 tested by the M^riter as to their efficiency in the de- 
 struction of bacteria, and any omissions which may 
 be observed in the tables are not due to any inten- 
 tion on the part of the writer to slight any of them, 
 or to any desire to call attention more forcibly 
 to one kind of machine than to another. It simply 
 means that the results of tests are not available. 
 
 189 
 
THE PASTEURIZATION OF MILK 
 
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CHAPTER VII 
 
 CHANGES IN THE CREAM LINE DUE TO THE 
 PASTEURIZATION OF MILK 
 
 Dealers who have had experience in the pas- 
 teurization of milk know that from time to time 
 they have trouble with what is known in the trade 
 as the "cream line" upon bottled milk. This may 
 mean that the line of demarcation between the 
 cream in the bottle and the skim milk just below it 
 is indistinct and faint^ or it may mean that no 
 cream at all is visible and the contents of the bot- 
 tle has the same color all the way through. Again, 
 it may mean that the apparent amount of cream 
 upon the milk is lessened. Either one of these 
 conditions is a reason for complaint on the part of 
 the customers. Dealers are therefore anxious to 
 obtain as great a volume of cream as possible upon 
 the milk sold by them, and are also anxious to get 
 the line of division as distinct as possible. Deal- 
 ers are sometimes at a loss to know why milk will 
 at one time show a good cream line, and at another 
 time, when the conditions are apparently the same, 
 the cream will be disturbed. 
 
 208 
 
FROM THE PRACTICAL VIEWPOINT 
 
 In I914<^ when the writer was connected with 
 the New York City Department of Health, the 
 Board of Health adopted certain modifications in 
 the regulations which had been in force concerning 
 the pasteurization of milk. Among these changes 
 were different rules concerning the temperature to 
 which milk must be heated and the length of time 
 for which it must be held at this temperature if 
 it was to be officially recognized as pasteurized 
 milk. 
 
 Prior to that time, the rules allowed a somewhat 
 wide variation in the heating temperatures, and a 
 corresponding variation in the length of time for 
 which the milk should be held. Thus milk which 
 was heated to 140° must be held at least twenty 
 minutes, while milk heated to 158° need be held 
 but three minutes. Between these extremes other 
 temperatures and holding times were allowed. This 
 sliding scale, as it might be called, allowed such a 
 latitude that milkmen who sold milk in cans only, 
 and were thus not much concerned with the cream 
 line, could heat the milk to a high temperature and 
 hold it for a short time. On the other hand, those 
 dealers who sold bottled milk, and who were desir- 
 ous to obtain as great a volume of cream as pos- 
 
 209 
 
THE PASTEURIZATION OF MILK 
 
 sible, could and usually did heat the milk to a low 
 temperature and hold it for a comparatively long 
 time. 
 
 A desire for uniformity of methods in the treat- 
 ment of milk led the authorities to adopt regula- 
 tions, in accordance with which one standard for 
 pasteurization only was applied, in all cases when 
 milk was heated for market use. The rules thus 
 adopted required all pasteurized milk to be heated 
 to 145° for thirty minutes. 
 
 Dealers who endeavored to comply with this rule 
 complained that they found the cream line was 
 affected, and that they could not comply with the 
 public requirements without injury to their busi- 
 ness. 
 
 In an effort to ascertain to what extent the 
 strict enforcement of the regulations would affect 
 the commercial quality of the milk, the writer made 
 an investigation. 
 
 This investigation was not made with the inten- 
 tion to determine what form of apparatus would 
 do the best work, nor to make any extended or ex- 
 haustive tests of any one form of apparatus un- 
 der varying surroundings and conditions. The ob- 
 ject was to see if it was possible and commercially 
 
 210 
 
FROM THE PRACTICAL VIEWPOINT 
 
 practicable to heat milk to 145° and hold it for 
 thirty minutes with the machines in use in the city 
 without seriously affecting the cream line. Any 
 results and data secured do not warrant the con- 
 clusions that the experiments indicate the essential 
 superiority of any of the apparatus described. 
 
 A little thought on the part of the reader will 
 make it clear that so many factors enter into the 
 problem that such conclusions would be unwar- 
 ranted. 
 
 In the same way that percentages of bacteria 
 reduction mean little unless we possess all the 
 data connected with the handling of the milk, 
 so likewise percentages of cream upon pas- 
 teurized milk are not alone of ultimate value as 
 showing that one apparatus is more satisfactory 
 than another. 
 
 A series of tests was made at several of the 
 pasteurizing plants in New York City at which 
 different forms of apparatus were being used, the 
 milk in these various plants being subjected to dif- 
 ferent degrees of temperature for varying lengths 
 of time. Samples of milk were taken to determine 
 the amount of cream which appeared upon the 
 bottled product. At the same time, the conditions 
 
 211 
 
THE PASTEURIZATION OF MILK 
 
 surrounding the handling of the milk were noted 
 in order to determine if other factors aside from 
 the temperature and holding time had any effect 
 upon the cream line. 
 
 In making the tests^ the samples of milk taken 
 were set in standard cream gauge glasses and the 
 actual percentage of cream showing upon the milk 
 as indicated thereon was carefully noted. These 
 tests were made during the early part of Decem- 
 ber, 1914. 
 
 First Test. — The first test was made at a plant 
 in which the pasteurizing apparatus consisted of 
 three tanks of the type shown in Fig. 13. Each 
 tank had a capacity of about forty cans of milk, 
 and after being filled the milk was heated by 
 means of a revolving coil of pipe extending through 
 the tank, through which coil hot water and steam 
 were forced. After the milk reached the proper 
 temperature, the steam was shut off in this coil 
 and the milk was held at the same temperature 
 for the desired length of time. It was then dis- 
 charged into a cooler consisting of a tank in which 
 were revolving disks, which is not here illustrated, 
 and immediately cooled. Since it required con- 
 siderable time for the tank to be fully emptied 
 
 212 
 
FROM THE PRACTICAL VIEWPOINT 
 
 after the discliarge was commenced, it is evident 
 that a part of the milk was held in the tank for 
 a considerably longer time than was that which 
 was first discharged from the tank. In making the 
 test, one tankfiil of milk was heated to a tempera- 
 ture of 142° and was held thereat for about thirty 
 minutes. The exact time of holding was not as- 
 certained on account of the fact that the milk was 
 being discharged from the tank at the time the 
 inspection began. A sample was taken from this 
 milk and placed in a cream gauge, which was then 
 packed in ice and allowed to stand for four hours, 
 at the end of which time 15 per cent, of cream ap- 
 peared upon the cream gauge. 
 
 A second sample was taken from one of the 
 tanks in which the milk had been heated to a tem- 
 perature of 116°, and held thereat for thirty-four 
 and a half minutes. The sample here taken was 
 allowed to stand packed in ice for four hours, at 
 the end of which time 13 per cent, of cream ap- 
 peared upon the gauge. A third sample was taken 
 from the same tank, but it was taken from that 
 milk which was last discharged from the tank. 
 This milk, therefore, had been held in the tank for 
 one hour and twenty-three minutes. This sample 
 
 213 
 
THE PASTEURIZATION OF MILK 
 
 was also set in ice for four hours and showed 8 per 
 cent, of cream upon the gauge. 
 
 A fourth sample was taken from a second tank 
 in which the milk was heated to a temperature of 
 146° and held thereat for exactly thirty minutes. 
 This milk showed 15 per cent, of cream upon the 
 gauge. 
 
 The method of handling the milk at this plant 
 should be noted. Milk was poured from the cans 
 into a dumping tank on the ground floor. It was 
 then pumped to a small tank upon the third floor 
 of the building, thence flowed through a centrifugal 
 clarifier, such as shown in Fig. 32, and then flowed 
 directly into the pasteurizing tanks. 
 
 Second Test. — A test was also made in another 
 milk plant in which the same form of pasteurizing 
 apparatus was installed. In this plant, the milk 
 was pumped from the receiving vat on the gound 
 floor into a tank upon the second floor, from which 
 the milk flowed through a clarifier and was then 
 discharged into a mixing vat, from which it flowed 
 into the various pasteurizing tanks. The opera- 
 tion of this plant was similar to that in the plant 
 previously described, except that, in the first in- 
 stance, the water which was forced through the 
 
 214. 
 
FROM THE PRACTICAL VIEWPOINT 
 
 heating coil of the tank was heated by means of a 
 steam jet, injecting steam directly into the water 
 pipe, wliereas, in the second instance, water was 
 heated in a tank outside of the pasteurizing tank 
 and was pumped, after the heating, directly into 
 the heating coil, it being the belief that if the 
 water was heated in this manner there was less 
 danger of the milk becoming scorched on account 
 of the water coil having been heated to a tempera- 
 ture which was excessive 
 
 At this second plant the first sample was taken 
 from the raw milk before it had passed through 
 the clarifier. This sample was allowed to stand 
 in ice for eleven hours, at the end of which time 
 19% per cent, of cream appeared upon the gauge. 
 A Babcock test was made of this milk and it was 
 found to contain 3.8 per cent, of butter fat. A 
 second sample was taken, which was as nearly as 
 possible from the same milk, after it had passed 
 through the clarifier. This sample, after standing 
 for eleven hours, showed 17 per cent, of cream on 
 the gauge. This milk also contained 3.8 per cent, 
 of butter fat. A third sample was taken from one 
 of the pasteurizing tanks in which the milk was 
 heated to 145° and was held in the tank for thirty- 
 
 215 
 
THE PASTEURIZATION OF MILK 
 
 three minutes, at which time the temperature was 
 found to be 11214° F. This sample, upon being 
 set, showed 12 per cent, of cream in the cream 
 gauge and contained 3.8 per cent, of butter fat. 
 The fourth sample was taken from the same tank 
 of milk, but when the tank was nearly empty. 
 The milk had been standing in this tank for one 
 hour and twenty minutes. It had been, however, 
 cooled to a temperature of 60° F. by means of 
 cold water pumped through the revolving coil. 
 A sample of this milk, upon setting, showed 15 
 per cent, of cream in the cream gauge and con- 
 tained 3.8 per cent, of butter fat. 
 
 It was thought possible that the speed of cool- 
 ing of milk might have an effect upon the cream 
 line. Therefore two samples of milk were taken, 
 one of which had a temperature of 135° F. This 
 sample was allowed to stand un-iced until cooled 
 by air contact to a temperature of about 40° F. 
 The second sample of milk was taken from the 
 same batch of heated milk, but this sample was 
 taken after the milk had been quickly cooled in 
 the cooling apparatus to a temperature of 32° F. 
 After setting, these two samples showed no appre- 
 ciable difference in the cream content. This indi- 
 
 216 
 
FROM THE PRACTICAL VIEWPOINT 
 
 cated that the speed of cooling had little or no 
 effect upon the rising of the cream in the milk. 
 
 The tests made at these two plants indicated 
 that it was entirely possible to heat milk to 145° 
 F. and hold it for thirty minutes without materially 
 affecting the volume of the cream contained in the 
 bottled milk, and that milk heated to 145° F. 
 showed the same amount of cream as that which is 
 heated to 142° F. 
 
 Third Test. — A test was made at another plant 
 where the same form of apparatus for pasteuriz- 
 ing was in use. During this test a sample was 
 taken from a tank in which the milk was heated 
 to a temperature of 141° and held there for sixty 
 minutes. This sample, after standing a sufficient 
 length of time, showed a cream content of 15 per 
 cent. A second sample was taken of raw milk 
 which had already been passed through the clari- 
 fier, and this milk was found to contain 1 5 per cent, 
 of cream. A third sample was taken from a tank in 
 which the milk had been heated to 145° and held 
 thereat for sixty minutes. This milk, after stand- 
 ing, showed no cream at all upon the cream gauge. 
 
 The results here obtained did not correspond 
 with those obtained at the two other plants where 
 
 217 
 
THE PASTEURIZATION OF MILK 
 
 the same apparatus was in use. No apparent rea- 
 son could be seen for the variation. Milk at this 
 plant, as received from the patrons, was allowed 
 to flow from the weigh vat into the mixing vat, 
 from which it was pumped to a vat upon the sec- 
 ond floor, thence it flowed into a clarifier, from 
 which it was discharged into a large mixing vat on 
 the same floor. It then flowed by gravity to the 
 pasteurizing vats on the first floor. 
 
 Fourth Test. — A further test was made at an- 
 other pasteurizing plant, in which the milk was pas- 
 teurized by means of a heater and holder, shown 
 in Figs. 5 and 22. In this heater the milk was 
 forced between two concentric cylinders, in each 
 of which hot water was contained, having a tem- 
 perature of 159°. The milk while being heated 
 was kept in agitation by the rapid revolution of 
 one of the cylinders above referred to. After 
 heating, the milk flowed by gravity into a series of 
 insulated tanks, in each of which it was held for 
 twenty-four minutes. On account of the fact, how- 
 ever, that milk as discharged from the heater 
 flowed first into a tank from which the various 
 holding tanks were filled, and on account of the 
 added fact that when these tanks were discharging 
 
 218 
 
FROM THE PRACTICAL VIEWPOINT 
 
 the milk, it flowed into a second tank before being 
 convej'^ed to the cooling apparatus, it is probable 
 that the milk was actually held at the highest tem- 
 perature for a period of at least twenty-seven 
 minutes. 
 
 A sample was taken from the raw milk before 
 being clarified. This milk, upon setting, was found 
 to contain 15 per cent, of cream and to have a fat 
 content of S.9 per cent. A second sample was 
 taken from milk which had been heated to 145° 
 F., and, after holding, was set and found to con- 
 tain 10% per cent, cream and 3.9 per cent, butter 
 fat. A third sample was taken from milk which 
 was heated to 144°, and was found to contain 8 
 per cent, of cream and 3.9 per cent, butter fat. A 
 fourth sample was taken from milk which was 
 heated to 142°, and was found to have a cream 
 content of 8 per cent, and 3.9 per cent, butter fat. 
 
 These results indicated that the milk which was 
 heated to 145° contained a greater percentage of 
 cream, by volume, than that which was heated to 
 142°. The reason for this was not apparent. The 
 milk pasteurized at this plant was received from 
 the railroad in cans which had been shipped from 
 the country. The milk was dumped from these 
 
 219 
 
THE PASTEURIZATION OF MILK 
 
 cans into a large dump vat, from which it was 
 pumped to a receiving vat upon the second floor 
 and was thence allowed to flow through a clarifier, 
 from which it was discharged into a large mixing 
 vat and thence flowed directly to the milk heater. 
 
 Fifth Test. — This test was made at a plant at 
 which the milk was pasteurized by means of a 
 heater somewhat similar to that shown in Fig. 3. 
 The holder was like Fig. 21. In this heater the 
 milk is forced between two water-heated cylin- 
 ders, in one of which the water was at a tempera- 
 ture of l65°, and in the other of which the tem- 
 perature of the water was nearly at the boiling 
 point. The milk, while being heated, was kept in 
 agitation by means of a revolving arm, which was 
 so arranged that it moved between the two heat- 
 ing surfaces. The milk, after heating, was held 
 in a series of eight water-jacketed tanks, the water 
 surrounding the tanks being kept at a temperature 
 of from 145° to 150° F. The milk, while in this 
 holding tank, was kept in agitation by means of re- 
 volving metal stirrers. 
 
 A sample was first taken from one of the hold- 
 ing tanks in which the milk was heated to a tem- 
 perature of 143° F. and held there for thirty 
 
 220 
 
FROM THE PRACTICAL VIEWPOINT 
 
 minutes. This sample, when set, was fomid to 
 have 11 per cent, of cream in volume, and the but- 
 ter fat content was 3.7 per cent. A second sample 
 was taken from a holding tank in which milk had 
 been heated to a temperature of 147° and held 
 for thirty minutes, the temperature of the milk at 
 its discharge being 146°. This milk showed 4 per 
 cent, of cream and a fat content of 3.8 per cent. 
 A third sample was taken from a tank in which 
 milk was heated to 145° and held for thirty 
 minutes. This milk, when set, showed 7 per cent, 
 of cream and 3.7 per cent, butter fat. A fourth 
 sample was taken from milk which had been heated 
 to 146° and held for thirty minutes. This milk 
 showed 3 per cent, of cream and 3.9 per cent, but- 
 ter fat. 
 
 These results indicate that with this form of ap- 
 paratus the cream line was seriously interfered 
 with, even at a temperature as low as 143°. The 
 milk, as received in this plant, was poured from 
 cans into a receiving tank upon the upper floor 
 of the building from which it flowed to an appa- 
 ratus on the floor below in which it was preheated 
 to 60° F. It then passed through centrifugal 
 clarifiers from which it was discharged into a large 
 
 221 
 
THE PASTEURIZATION OF MILK 
 
 tank upon the receiving floor. From this tank it 
 flowed by gravity to the pasteurizers on the floor 
 below. 
 
 Sixth Test. — This test was made at a plant in 
 which the milk was heated by means of an appa- 
 ratus shown in Fig. 11, where the milk is heated 
 by means of what is known as a Multitube Heater. 
 In this form of heater a series of large tubes are 
 so arranged that several smaller tubes extend 
 through them. The milk is forced through the 
 inner tubes, while hot water is forced through the 
 large surrounding tubes. After heating, the milk 
 is discharged into a series of eight holding tanks 
 similar to those described in test No. 5. The water 
 which is used to heat the milk in this apparatus is 
 itself heated in a tank outside of the milk heater 
 and is kept at a temperature varying between 144° 
 and 163°, the temperature rarely exceeding 154°. 
 From this tank the water is pumped to the milk- 
 heating apparatus. 
 
 The conditions at this plant were apparently fa- 
 vorable for securing good results. The fact that 
 the temjjerature of the heating water was carefully 
 controlled, made it impossible to superheat or 
 scorch any of the milk. The first sample of milk 
 
 222 
 
FROM THE PRACTICAL VIEWPOINT 
 
 was taken from raw milk before it was clarified. 
 This sample, when set, showed 131/2 per cent, of 
 cream and 3.4 per cent, butter fat. The second 
 sample was taken from one of the holding tanks 
 in which the milk was heated to a temperature of 
 146° and held thereafter for tliirty minutes. This 
 sample, when set, showed no cream whatever on 
 the cream gauge, the fat being evidently evenly 
 distributed throughout the entire body of the milk. 
 This milk contained 3.5 per cent, of butter fat. 
 A third sample was taken from one of the holding 
 tanks in which the milk was heated to 143° F. 
 and held for thirty minutes. This milk showed, 
 upon standing, 10 per cent, of cream and 3.7 per 
 cent, butter fat. Sample No. 4 was take^ from a 
 tank in which the milk was heated to 146° F. and 
 held for thirty minutes. This sample showed 5 
 per cent, of cream and 3.35 per cent, butter fat. 
 
 The results here obtained indicate that with this 
 apparatus if the milk was heated above 143° the 
 cream would be seriously affected. 
 
 Seventh Test. — A test was made at still an- 
 other plant in which the milk was heated by means 
 of the pasteurizer shown in Fig. 9- In this appa- 
 ratus the milk is forced through a series of pipes 
 
 223 
 
THE PASTEURIZATION OF MILK 
 
 which are enclosed in a large chamber which is 
 filled with hot water. The apparatus somewhat 
 resembles the tubular boiler. After heating, the 
 milk is held in three upright cylindrical Park hold- 
 ing tanks, the milk passing through the entire se- 
 ries. In this holding apparatus tests previously 
 made indicated that milk is held for from thirty- 
 live to forty minutes. 
 
 In making this test, the first sample was taken 
 from the raw milk. This sample, when set, showed 
 14 per cent, of cream and 3.8 per cent, butter fat. 
 A second sample was taken from milk which was 
 heated to a temperature of 143° and held for from 
 thirty-five to forty minutes. This sample, when 
 set, showed 14 per cent, of cream and 3.8 per cent, 
 butter fat. In order to vary the experiment the 
 temperature of the milk entering the holder was 
 then raised to 145°, at which temperature the milk 
 was maintained until the process of pasteurizing 
 was completed for the day. The milk in the filled 
 holding tanks was allowed to stand for thirty 
 minutes and a sample was taken from that which 
 was being discharged from the holding tank, which 
 showed, on standing, 14 per cent, of cream and 
 3.85 per cent, butter fat. A fourth sample was 
 
 224 
 
FROM THE PRACTICAL VIEWPOINT 
 
 taken from the milk which was last discharged 
 from the holder. This milk had been in the holder 
 for exactly sixty minutes. Upon standing, this 
 milk showed 9 per cent, of cream and S.7 per cent, 
 butter fat. 
 
 These results indicated that milk could be heated 
 to 145° and held for thirty minutes without any 
 injurious effect upon the cream line being pro- 
 duced, but that if the milk was held for an hour, 
 the cream line was considerably affected. 
 
 Eighth Test. — A further test was made at a 
 pasteurizing plant in which the milk was heated 
 by means of the heater shown in Fig. 7, and held 
 in the holder illustrated in Fig. 27. In this appa- 
 ratus the milk is forced through a series of pipes 
 which are themselves enclosed in a larger pipe 
 through which hot water is forced. The holding 
 apparatus consists of a series of large tubes 
 through which the milk is allowed to flow. It re- 
 quires about thirty-five minutes for the milk to be 
 discharged through the holding tubes. 
 
 A sample was taken from the raw milk, before 
 clarifying. This was found to contain 15^2 per 
 cent, of cream and 3.5 per cent, butter fat. A sec- 
 ond sample was taken from milk which had been 
 
 225 
 
THE PASTEURIZATION OF MILK 
 
 clarified, and this was found to contain 12 per cent, 
 cream and 3.6 per cent, butter fat, there being an 
 apparent reduction of 3% per cent, of cream vol- 
 ume due to the clarifying process. A third sam- 
 ple was taken from milk leaving the holder at a 
 temperature of 142°. This was found to contain 
 8 per cent, cream and 3.7 per cent, butter fat. A 
 fourth sample was taken from milk leaving the 
 holder at a temperature of 145°. This showed 7 
 per cent, of cream and 3.6 per cent, butter fat. 
 
 The results here obtained indicated that milk 
 which is heated to 145° shows about the same 
 amount of cream, by volume, as that which is 
 heated to 142°, but the milk heated to either tem- 
 perature showed but little more than half the 
 amount of cream which was found in the raw 
 milk. 
 
 The milk at this plant was received in the 
 dumping tank on the first floor, from which it was 
 pumped to a tank upon the pasteurizing floor, and 
 thence flowed through a centrifugal clarifier into 
 the mixing tank. From this tank it was pumped 
 through the heater and holder, and after being 
 discharged from the holder was again pumped 
 through the cooler. 
 
 226 
 
FROM THE PRACTICAL VIEWPOINT 
 
 Summary of Results 
 
 All the tests made indicate that when milk is 
 cleaned by a centrifugal clarifier, the volume of 
 cream in the milk suffers a reduction of 2 per cent, 
 to 3 per cent. 
 
 The number of tests made was probably not 
 sufficient to warrant the drawing of absolutely 
 definite conclusions. It was evident, however, that 
 the volume of cream in bottled milk was influenced 
 by various factors, some of which are apparently 
 little understood. These factors include: 
 
 (1) The temjDerature to which the milk is 
 heated. 
 
 (2) The length of time for which milk is held 
 at the high temperature. 
 
 (3) The temperature of the heating medium 
 with which the milk comes in contact during the 
 heating process. 
 
 (4) The clarification of the milk. 
 
 (5) The type of apparatus used in treating the 
 milk. 
 
 (6) The amount of agitation to which the milk 
 is subjected, especially while hot. 
 
 This last factor has a greater influence upon 
 
 227 
 
THE PASTEURIZATION OF MILK 
 
 the cream line than is ordinarily appreciated. It 
 has been stated to the writer, that in one instance 
 where the cream line was materially reduced dur- 
 ing the pasteurization process, the experiment was 
 made of reducing the speed of the agitator which 
 kept the hot milk in motion. After the speed had 
 been so reduced it was found that the cream line 
 upon the milk resumed its normal character. 
 
 It will also be noted from the foregoing descrip- 
 tion of the various methods of handling milk that 
 in those plants where there was most agitation of 
 the milk, and especially where the pumping of 
 hot milk was practiced, the most difficulty with the 
 cream line was experienced. There are possibly 
 other factors which affect the cream line, among 
 which may be: 
 
 1st, the age of the milk before pasteurization. 
 
 2nd, the grade of cows from which the milk was 
 produced. 
 
 3rd, the fact that milk has or has not been frozen 
 before being treated. 
 
 The tests made proved that it is entirely pos- 
 sible, under the most favorable conditions, to heat 
 milk to 145° and hold it for thirty minutes without 
 producing any injurious effect upon the cream line. 
 
 228 
 
FROM THE PRACTICAL VIEWPOINT 
 
 It is also doubtless true, however, that with some 
 types of apparatus in use by the milk dealers and 
 with some conditions under which milk is handled, 
 a real difficulty is experienced in obtaining satis- 
 factory results. 
 
 The chart shown in Fig. 34, drawn by Dr. North, 
 indicates graphically the temperatures and holding 
 times within which it is safe to heat milk without 
 affecting the cream line. Such a chart cannot show 
 the other factors which also affect the results, such 
 as the amount of agitation, etc. 
 
 If the milk is being heated and an attempt is 
 made to keep the milk at a temperature no lower 
 than 145° F., it is almost certain that the tempera- 
 ture will at times reach from 146 to 148° or higher, 
 and that it will at times be held longer than thirty 
 minutes. It is almost mechanically impossible to 
 so control the temperature of milk while heating 
 that there will not be considerable variation. 
 
 The agitation probably has the effect of break- 
 ing up the fat globules into smaller masses. Since 
 each globule of fat is surrounded with a film of 
 casein or skim milk, which is heavier than the fat, it 
 is evident that as the mass of fat becomes smaller, 
 the proportional amount of the surrounding skim 
 
 229 
 
THE PASTEURIZATION OF MILK 
 
 TIME. AMD TLMPLRATURE. FOR 
 ntf MILK PASTEURIZATION. 
 
 /O' 10' 30' 40' 
 
 Tl ME. IN MINL/TE-d 
 
 Fig. 34 
 230 
 
FROM THE PRACTICAL VIEWPOINT 
 
 milk becomes greater, till we reach a point when 
 the buoyant fat cannot lift the heavier envelope, 
 and our balloon of fat stays down. 
 
 Just why the high heat and the long holding 
 scatters the fat permanently through the body of 
 the milk is not so clear. It may be due to chemical 
 changes which occur. 
 
 In the pasteurizing equipment described on 
 pages 124 and 131 it is claimed that the superheat- 
 ing of the held milk has a beneficial effect upon 
 the cream lines. 
 
 The tables following show graphically the re- 
 sults of the tests made. They indicate the varied 
 conditions under which milk was handled in the 
 various tests and the percentage of the cream upon 
 each sample as well as the percentage of butter fat 
 which was determined by the Babcock test. 
 
 231 
 

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 239 
 
CONCLUSION 
 
 In conclusion, it may not be amiss to say that all 
 the indications lead to the conviction that the pas- 
 teurization of milk is not, as some have claimed, a 
 fad. It is coming more and more into use, as a 
 recognized sanitary measure, which is at present 
 necessary. Whether a time may come when it will 
 be safe for large commimities to consume their 
 milk unheated is a question which at present is not 
 a subject for practical consideration. The South 
 and West, which have been slow to recognize the 
 value of pasteurization, are coming into line, and 
 the teaching of practical methods of handling ap- 
 paratus used in pasteurizing milk is a wise thing 
 for the dairy schools to take up. Practical meth- 
 ods of controlling the actual operation of pasteuriz- 
 ing plants should be taught, and instruction should 
 be available for inspectors employed by munici- 
 palities, as well as for those who are to become 
 such inspectors, in order that they may be equipped 
 to render the most useful service to the com- 
 munities when they assume their duties. 
 
 240 
 
THE PASTEURIZATION OF MILK 
 
 Other methods may be discovered by which milk 
 may be rendered safe with less trouble and ex- 
 pense, but none such are now in sight, and until 
 they appear our towns and cities must depend upon 
 the proper application of heat to render milk safe 
 as food. 
 
 It is due to the citizens that the actual treatment 
 of the milk be so intelligently supervised and con- 
 trolled that it will in reality be as safe as the 
 people have a right to expect. 
 
 241 
 
INDEX 
 A 
 
 PAGE 
 
 Adulteration of Milk 5,6 
 
 Agricultural Department 2 
 
 Ahlborn 11 
 
 Air-compressors 135 
 
 Avers (and Johnson) 9? 86, 155 
 
 B 
 
 Boards of Food Control 2 
 
 Bottle-capping 177-180 
 
 Bottle-cleaning 163-175 
 
 Bottle-filling 176 
 
 Bottles, Paper 180-182 
 
 Bovine Tuberculosis 18-22 
 
 C 
 
 Capping Bottles 177-180 
 
 Chemical Changes 27 
 
 Cleaning and Clarifying 150-155 
 
 Color Test 115,116 
 
 Compressed Air 135 
 
 Conclusion 210 
 
 243 
 
INDEX 
 
 PAGE 
 
 Containers, Washing of 163-175 
 
 Control (Official) of Pasteurization 32-34 
 
 Controllers, Temperature 27, 133-140 
 
 Cooling 155 
 
 Coolers, Open 155-160 
 
 Tank 160-161 
 
 Tubular 162 
 
 Cream Line 21, 29, 208-239 
 
 D 
 
 Department of Health, Reprints 9 
 
 New York City 27, 43, 94, 209 
 
 Denmark 11, 12 
 
 E 
 
 Efficiency of Apparatus 185-207 
 
 Electric Process 90, 91 
 
 Enzymes 30 
 
 F 
 
 Filling Bottles 176 
 
 Fresca 11 
 
 G 
 
 Geneva Experiment Station 19, 158 
 
 244 
 
INDEX 
 H 
 
 PAGE 
 
 Health Department 2 
 
 New York City 9, 27, 43, 94, 209 
 
 Heaters 43 
 
 First Type , 44-47 
 
 Second Type 47-56 
 
 Third Type 56-65 
 
 Fourth Type 65-77 
 
 Fifth Type 77-89 
 
 Holding Time, Method of Calculation... 96,103 
 
 Holders 94-107 
 
 Absolute Type 94-1 1 1 
 
 Points to be Observed in 108, 109 
 
 Continuous or Flow Type 111-132 
 
 Disturbances of Holding Time. .113, 114 
 
 Horizontal Tank 124-126 
 
 Park Tank 1 1 1-123 
 
 Testing of Holding Time 115, II6 
 
 Tubular 126-129 
 
 Home Pasteurization 183, 184 
 
 I 
 
 Infection of Milk 4, 5, 18-22 
 
 245 
 
INDEX 
 
 J PAGE 
 
 Jacob! 13 
 
 Johnson 9^ 86, 155 
 
 K 
 
 Kiilp 158 
 
 M 
 
 Milk Dealers' Organizations 6, 7 
 
 Milk, Changes Due to Pasteurization. ... 27 
 
 Methods of Official Control 32-34 
 
 N 
 New York City 9, 15, 27, 43, 94, 209, 212 
 
 O 
 
 Ozone Treatment 92 
 
 P 
 
 Park 20, 23, 111 
 
 Pasteur 10 
 
 Paper Bottles 180-182 
 
 246 
 
INDEX 
 
 PAGE 
 
 Pasteurization in General 1-42 
 
 Pasteurization Literature 7—9 
 
 Pasteurization, Home 183, 184 
 
 Regulations 27 
 
 Pasteurized Milk, Requirements for Secur- 
 ing Good Results 31, 32 
 
 Pasteurizer, Danish 11, 12 
 
 Pasteurizing Plant, Requirements for Sat- 
 isfactory Equipment 36-42 
 
 Pasteurizing in Vacuum Pans 89, 90 
 
 Percentage of Bacterial Reduction 185-207 
 
 Public Health Reports 18 
 
 Pumjos 39 
 
 R 
 
 Recorders — Temperature 140-149 
 
 Reid 11 
 
 Rosenau, M. J 9, 22, 23, 25, 183 
 
 Ruehl (and Kulp) 158 
 
 S 
 
 Schores 25, 27 
 
 Septic Sore Throat 17, 18 
 
 Sheele 10 
 
 247 
 
INDEX 
 
 PAGE 
 
 Sohxlet 13 
 
 Storch Test 32 
 
 Superheating of Milk 131 
 
 T 
 
 Temperature Controller 27, 133-140 
 
 Temperature Test, Holding Tanks 115,116 
 
 Temperature Recorders 140-149 
 
 Testing Cleaned Containers 174, 175 
 
 Testing of Holding Time 115, ll6 
 
 Thermal Death Point 27 
 
 Tuberculosis 12, 18-21 
 
 Typhoid Fever 17 
 
 U 
 
 Ultra Violet Rays 92 
 
 V 
 
 Vacuum Pans 89, 90 
 
 W 
 
 Washing of Containers 163-175 
 
 Winslow 18 
 
 248 
 
PRINTERS 
 
LIBRARY OF CONGRESS 
 
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