UNIVERSITY OF CALIFORNIA AGRICULTURAL EXPERIMENT STATION 
 
 *w* a ■ w~w ~.r- .__.._...._....- BENJ. IDE WHEELER, President 
 
 COLLEGE OF AGRICULTURE THOMAS fqrsyth hunj ,_ ano ,__ 
 
 BERKELEY h. e. van norman, vice-director and dean 
 
 University Farm School 
 
 CIRCULAR No. 179 
 October, 1917 
 
 FACTORS OF IMPORTANCE IN PRODUCING 
 MILK OF LOW BACTERIAL COUNT 
 
 By C. L. EOADHOUSE 
 
 Galvanized-iron sterilizing tank for dairy utensils. 
 
 Since the keeping quality of milk is greatly influenced by the 
 presence of bacteria, a study of the sources of these organisms in 
 dairies and the practical methods of limiting their numbers in milk 
 is of great importance to all dairjrmen and more especially to those 
 engaged in producing or distributing market milk. 
 
Many city health departments in carrying out the provisions of 
 the new state dairy law are enforcing the grading of milk and, in 
 order that dairymen may sell the higher grades, it is required among 
 other things that the number of bacteria be kept within certain limits. 
 It is the purpose of this circular to point out briefly the principal 
 sources of these organisms and to explain the care of milk which 
 leads to a lower bacteria content. 
 
 BACTERIA AND THEIR SOURCES 
 
 Bacteria are microscopic single-celled organisms, varying in size 
 and shape, and are present everywhere in nature. Normally the 
 common bacteria in limited numbers are not injurious, but when they 
 gain entrance to milk under favorable conditions they grow rapidly; 
 therefore, in a few hours they may seriously interfere with its quality 
 as food and consequently decrease its commercial value. Bacteria 
 in milk originate principally from the interior of the cow's udder, 
 body of cow, the milker, milking stable and utensils. 
 
 INTERIOR OF THE COW 'S UDDER 
 
 Bacteria exist in the udders of all cows, the number varying in 
 different animals. An examination of 1230 samples of milk direct 
 from the udders of seventy-eight cows at the New York Agricultural 
 Experiment Station showed an average of 428 bacteria per cubic 
 centimer. It is believed that organisms gain entrance to the udder 
 through the orifice of the teat and that they are sufficiently numerous 
 in all udders so that it is not possible to draw any but minute quan- 
 tities of milk directly from the udder which are free from bacteria. 
 Nothing can be done to lessen the bacteria content of the normal udder 
 except to keep cows out of deep mud, particularly the mud of the 
 stable yard. This is usually permeated with manure bacteria and 
 irritating material which encourages udder trouble and the subsequent 
 increased number of bacteria which frequently accompany such con- 
 ditions. 
 
 Animals which have apparently recovered from previous attacks 
 of udder trouble, in some instances, yield milk with an enormous 
 number of bacteria. Milk from such animals if mixed with the milk 
 from the remainder of the herd may increase the average bacteria 
 
 We desire to acknowledge our indebtedness to Mr. F. H. Bothell of Los 
 Angelefl and Dr. G. H. Hart, formerly of the Los Angeles Health Department, 
 for in formation pertaining to the use of galvanized-iron sterilizers. — C. L. R. 
 
content to a marked extent. Bacteria from this source are us lally 
 of less importance in clean milk production than the other soum s of 
 bacteria which are to be mentioned. 
 
 THE BODY OF THE COW GREATEST SOURCE OF DIRT IN MILK 
 
 The skin of the cow is one of the important sources of the bacteria 
 causing souring of milk. On account of her thick coat of hair and 
 the fact that she 'frequently is permitted to lie in a dusty, muddy or 
 manure-covered corral, a great deal of dirt and dust laden with 
 bacteria are enmeshed in and clinging to the hair of the animal's body 
 to be readily dislodged and dropped into the pail during the milking 
 process. Good dairy practice includes the washing of the udder and 
 teats before milking by the aid of a hose when filth is present and the 
 wiping of the udder with a damp cloth at other times, whether visible 
 dirt is present or not. As a means of lessening the dirt and bacteria 
 gaining access to milk from the exterior of the animal the use of 
 a small-top milk pail is of great assistance since more than one-half 
 of .the contamination that milk receives during the milking process 
 can be avoided by the use of this type of pail. 
 
 Where milking machines are used the greater part of the contam- 
 ination of milk from the body of the cow and the stable is eliminated, 
 but unless great care is used to thoroughly wash, brush and scald tin? 
 teat cups and rubber connections after each using and to keep them 
 in a chlorine or brine solution, or other acceptable mild antiseptic, 
 the bacteria content of the milk may be higher than where hand milk- 
 ing is practiced. A careful operator, with proper knowledge, who 
 personally attends to the washing and care of the milking-machine 
 parts may consistently produce milk with a low number of bacteria. 
 
 THE MILKER 
 
 The milker may become an important source of contamination of 
 milk, particularly if he is not clean about his person. His hands 
 and clothing may give off a great many bacteria to milk, especially 
 if he has been handling the feed and doing farm work preceding 
 milking and has failed to wash his hands thoroughly and put on a 
 clean milking suit before starting to milk. He should be furnished 
 with clean bedding, facilities for bathing and encouraged in all mat- 
 ters of personal cleanliness. The milker should be healthy and should 
 discontinue milking at any time a member of his family or household 
 should be suspected of having an infectious disease. Wet milking 
 should not be practiced and there should be facilities in every milking 
 stable for milkers to wash their hands. 
 
THE MILKING STABLE 
 
 The construction of the milking stable is of some importance in 
 clean milk production since the ledges resulting from a great amount 
 of scaffolding in the building leave a place for dust, dirt and spider- 
 webs to accumulate. These are easily blown off into the air of the 
 stable during milking and settle into the milk pail. 
 
 Storing the feed for dairy cows apart from the milking stable and 
 placing it before the cows at least one hour before milking is a means 
 of reducing the amount of dust in the stable at milking time. Sprink- 
 
 Fig. 1. — Uncovered milk pail. The 
 open-top pail is unsatisfactory for 
 use. 
 
 Fig. 2. — Covered milk pail. The 
 hood may be added to the ordinary 
 type of pail as here shown. 
 
 ling the hay before placing it before the cows is practiced by some 
 dairymen to keep down the dust in the stable. Recent experiments 
 at the New York Agricultural Experiment Station have shown that 
 the contamination of milk in the stable from dust is of less importance 
 than has been believed in the past. 
 
 CLEANSING OF UTENSILS 
 
 The cleanliness and proper care of dairy utensils can be considered 
 the most important item in producing milk with a low bacteria count. 
 Proper cleansing of dairy utensils, briefly described, consists in first 
 rinsing them in cold or lukewarm water to remove milk and any 
 sediment that may be present, then brushing with a washing-solution 
 
to thoroughly clean them, followed by rinsing in warm water to re- 
 move the washing-solution. The purpose of removing the milk and 
 any sediment that may be present in the utensils by the first rinsing 
 is to keep the washing-solution as clean as possible. Where this 
 method of cleaning is not practiced dried milk is frequently found 
 clinging to dairy apparatus, being baked upon the tinware from 
 scalding it before all milk is removed. The washing-solution will 
 become polluted with sand, flies and manure from the bottom of the 
 milk pails if this first rinsing is ignored. 
 
 Fig. 3. — Covered milk pail for use with cheese cloth and cotton strainer over 
 opening. Milk is poured out through spout. 
 
 The washing-solution prepared from sal soda or from one of the 
 commercial washing powders should be used warm and with thorough 
 brushing of all surfaces of the milk containers and utensils, and should 
 dirt and other foreign material accumulate in it a fresh solution 
 should be prepared. 
 
 The third step in cleaning the utensils consists in rinsing with 
 clean warm water to remove the washing-solution and leave a fresh, 
 clean surface for the milk. Utensils cleaned in this way may still 
 contain thousands of bacteria although the number present would 
 be much lower than in poorly-cleaned utensils. To destroy all 
 bacteria in utensils these must be thoroughly sterilized with steam 
 or boiling water. 
 
UNSTERILIZED UTENSILS THE GREATEST SOURCE OF BACTERIA 
 
 IN MILK 
 
 The greatest source of bacteria in milk is unsterile utensils and 
 these bacteria are the most important ones to destroy because they are 
 accustomed to growing in milk and reproduce in it extremely fast 
 when milk is placed into such containers. Many of the dust bacteria 
 develop in milk more slowly and some of them perish in milk because 
 it is not suitable for their growth and reproduction. 
 
 All dairy utensils, including milk cooler, pails, strainer cloths, 
 milk cans, vats and bottles should either be placed into a tightly-closed 
 compartment and treated with live steam under pressure for twenty 
 minutes or boiled for twenty minutes in the type of sterilizer shown 
 in figure 2, if every effort is to be made to lessen the number of 
 bacteria in milk. 
 
 Strainer cloths, after washing, should be either spread out so that 
 all parts of the cloth are in direct contact with hot steam, or they 
 should be boiled. Unless they are sterilized thoroughly by one 
 or the other of these methods they may become the greatest source 
 of bacteria in milk. 
 
 The usual method of applying steam directly to dairy utensils 
 from a pipe or steam hose is not effective although it has been shown 
 that with a boiler pressure of thirty pounds, where the steam is 
 applied for at least fifteen seconds, most of the bacteria are destroyed. 
 
 REDUCING BACTERIAL COUNTS BY SIMPLE METHODS 
 
 Although milk is constantly collecting bacteria in its journey from 
 the cow to the consumer and in producing high-grade milk every step 
 in its handling should be guarded, as already described, it is still 
 possible to produce a very satisfactory quality of milk without atten- 
 tion to all of the details heretofore mentioned if extreme care is given 
 to the sterilization of utensils and the milk is cooled as thoroughly as 
 possible with cold water and delivered within five or six hours after it 
 is produced. At the end of this time the milk must be either pasteur- 
 ized or immediately cooled to 50° F. and kept below that temperature; 
 otherwise it will deteriorate rapidly. This procedure is practical for 
 many dairymen producing market milk where the milk is deliver* d 
 to city milk plants. Most distributors of milk in cities now have 
 facilities either for pasteurizing or cooling milk to a low temperature 
 so that with thorough sterilization of utensils by the producer and 
 the early delivery of the milk to the city milk plant the bacteria 
 
7 
 
 content when it reaches the distributor may be very low as compared 
 with the result when this procedure is not carried out. 
 
 * 8"+ 
 
 $r£/?/L/J?£& TA/V/C/W PLACE OI/£J? fU&A/ACE— 
 
 Fig. 4. — A combination hot-water heater and steam sterilizer for dairy utensils. 
 
 AN INEXPENSIVE STERILIZER 
 
 For small dairies producing market milk, or for large dairies 
 shipping cream, in case a steam boiler is not available, very satisfac- 
 tory sterilization can be accomplished by placing all dairy utensils 
 
8 
 
 into a covered galvanized-iron tank, such as shown in figure 4, and 
 boiling them for twenty minutes. 
 
 The sterilizer tank may be made of galvanized iron of any weight 
 or quality, but unless it is constructed of heavy high-purity galvanized 
 
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 Figure 5 
 
 iron it will soon burn out. Those made from the best material of 
 No. 16 or No. 14 gauge will be the cheapest in the end on account 
 of the increased durability, if they are properly cared for. If the 
 tank is made of No. 16 gauge iron the top may be only No. 20 
 gauge, which will be less expensive and just as durable since the 
 
cover is subjected to less wear than the tank. Wood is the fuel most 
 commonly used in heating these sterilizers but in case an oil burner 
 is used an extra sheet of iron should be placed directly above the 
 flame ; otherwise the extreme heat from the oil burner will injure 
 the bottom of the sterilizer and decrease its durability. 
 
 Since the galvanized iron usually carried by plumbers does not 
 exceed thirty-six inches in width, the size of sterilizer cannot exceed 
 that shown in figure 4, if it is to be economically constructed. A 
 false bottom should be provided in the bottom of the tank to hold the 
 utensils above the boiling water. The heat from the steam accom- 
 plishes the sterilization and by keeping the utensils above the water 
 in the tank, they are less likely to rust when kept in the tank after 
 sterilization. 
 
 The false bottom may be constructed from *4 x 1 inch galvanized 
 bar iron, as follows : 
 
 Seven (7) parallel pieces five inches apart to be riveted to V4 x 1 
 inch end bars. The end bars are turned downward at right angles 
 three inches from each end to form supports and raise the false bottom 
 three inches from the bottom of the tank. The metal frame is given 
 greater strength by riveting a y s xl inch angle iron through the center 
 and parallel to the end bars. The ends of this also should be turned 
 at right angles to rest against the bottom of the tank. This size- 
 tank is sufficient for the sterilization of the cans and other dairy 
 utensils on dairies of the size previously stated. The sterilizing tank 
 may be filled twice with utensils in case it is not sufficiently large 
 to allow for sterilizing all utensils at one time. 
 
 SPECIFICATIONS FOR STERILIZING TANKS OF DIFFERENT 
 CONSTRUCTION 
 
 I. One Sterilizer. — Made from high-purity galvanized iron. Width 34VL> 
 inches, length 36 inches, height 28% inches. Body to be made from No. 16 
 galvanized iron and top to be No. 20 galvanized iron. All seams to be riveted 
 and soldered to render watertight. Upper edge to be equipped with y± inch 
 wire around outside and galvanized iron folded over in neat manner. Cover to 
 be flanged down 2 inches all around to make the cover perfectly tight. One side 
 of tank to be fitted with % inch faucet attached by means of a % inch galvanized 
 flange union. Sterilizer to be complete, ready for immediate use. 
 
 II. One Sterilizer. — Same as I, except with the f ollowing changes : Upper 
 edge to be equipped with % x 2 inch flat strip so as to make the cover perfectly 
 tight. Cover to be flanged down 4 inches all around. (This sterilizer will be 
 somewhat more expensive than I, but a higher temperature can be maintained 
 since the cover can be made to fit closer around the edges and confine the steam 
 more satisfactorily than in the case of I.) 
 
10 
 
 III. One Sterilizer. — Made from ordinary galvanized iron. Body and top 
 to be made from No. 2-4 gauge galvanized iron. All edges to be double seamed 
 and soldered to render watertight. Upper edges to be equipped with % inch 
 wire around outside and galvanized iron folded over in neat manner. Cover to 
 be flanged down 1 inch all around to make cover perfectly tight. One side 
 of tank to be fitted with % inch faucet attached by means of a % inch galvanized 
 flange union. Sterilizer to be complete, ready for immediate use. 
 
 The cost of galvanized-iron sterilizing tanks varies with the price 
 of galvanized iron, which at present is higher than average. From 
 figures obtained in the spring of 1917 the first sterilizer described 
 would cost about $22, the second about $27, and the third about $11. 
 
 USE OF STERILIZER 
 
 The sterilizer may be mounted over a brick or stone furnace. It 
 may be used, first, for heating water for washing utensils. After 
 water is drawn off at faucet and utensils are properly cleaned they 
 can be placed in the tank, which should contain about two inches 
 of water, cover placed in position and the utensils boiled for about 
 twenty minutes. Sterilizers of this type are now being used by many 
 dairymen supplying milk and cream to the cities of Los Angeles 
 and Seattle, and their use is believed to have been of material assist- 
 ance in reducing the number of bacteria in the milk from dairies in 
 those sections. After sterilizing the utensils they may be removed to 
 a screened milk room and turned over a draining-rack to dry. The 
 sterilizer will be more durable if water is drawn off and it is allowed 
 to dry after each using. 
 
 EFFECT OF TEMPERATURE AND AGE UPON BACTERIAL GROWTH 
 
 IN MILK 
 
 The temperature at which milk is kept is the most important 
 condition influencing the rate of growth of bacteria. 
 
 The milk-souring bacteria reproduce most rapidly when milk is 
 held at a temperature of 70° F. In order to avoid early souring of 
 milk and its rapid deterioration it must be held at a low temperature 
 even though it lias been produced in a clean manner. 
 
 Most bacteria do not grow in milk if it is kept below a temperature 
 of 40° F. In practical dairy work milk should either be cooled as 
 low as possible with cold water and delivered to the consumer within 
 five or six hours after it is produced, or cooled to a temperature below 
 50° P. and stored at that temperature until used. 
 
11 
 
 SUMMARY 
 
 1. Bacteria in milk originate from the udder, bod}' of the cow. 
 milker, milking stable and unsterilized utensils. 
 
 2. Unsterilized milk utensils are the greatest source of bacteria in 
 market milk. 
 
 3. The cooling of milk and its age are other important factors 
 influencing the bacteria content of milk. 
 
 4. Ideal sterilization of dairy apparatus consists in placing all 
 utensils, strainer cloths, bottles, etc., into a tightly-closed compartment 
 and treating with live steam under pressure of at least five pounds 
 for twenty minutes. 
 
 5. An inexpensive sterilizing tank for small dairies producing 
 market milk or large dairies shipping cream can be constructed from 
 heavy galvanized iron, and mounted over a brick or stone furnace 
 where utensils should be boiled for at least twenty minutes. 
 
STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION 
 
 REPORTS 
 
 1897. Resistant Vines, their Selection, Adaptation, and Grafting. Appendix to Viticultural 
 Report for 1896. 
 
 1902. Report of the Agricultural Experiment Station for 1898-1901. 
 
 1903. Report of the Agricultural Experiment Station for 1901-03. 
 
 1904. Twenty-second Report of the Agricultural Experiment Station for 1903-04. 
 
 1914. Report of the College of Agriculture and the Agricultural Experiment Station, July, 
 
 1913-June, 1914. 
 
 1915. Report of the College of Agriculture and the Agricultural Experiment Station, July, 
 
 1914-June, 1915. 
 
 1916. Report of the College of Agriculture and the Agricultural Experiment Station, July, 
 
 1915-June, 1916. 
 
 1917. Report of the College of Agriculture and the Agricultural Experiment Station, July, 
 
 1916 — June, 1917. 
 
 BULLETINS 
 
 No. 
 
 230. 
 241. 
 242. 
 246. 
 248. 
 
 249. 
 250. 
 251. 
 
 252. 
 253. 
 
 255. 
 257. 
 261. 
 
 262. 
 
 263. 
 264. 
 265. 
 266. 
 
 267. 
 268. 
 
 No. 
 113. 
 114. 
 115. 
 121. 
 
 124. 
 126. 
 127. 
 128. 
 129. 
 131. 
 133. 
 134. 
 135. 
 136. 
 137. 
 138. 
 139. 
 
 140. 
 
 141. 
 
 142. 
 
 143. 
 
 144. 
 145. 
 
 147. 
 148. 
 150. 
 151. 
 
 No. 
 
 Enological Investigations. _ 270. 
 Vine Pruning in California, Part I. 
 Humus in California Soils. 
 
 Vine Pruning in California, Part II. 271. 
 
 The Economic Value of Pacific Coast 272. 
 
 Kelps. 273. 
 Stock-Poisoning Plants of California. 
 
 The Loquat. 274. 
 Utilization of the Nitrogen and Organic 
 
 Matter in Septic and Imhoff Tank 275. 
 
 Sludges. 
 
 Deterioration of Lumber. 276. 
 
 Irrigation and Soil Conditions in the 277. 
 
 Sierra Nevada Foothills, California. 278. 
 
 The Citricola Scale. 279. 
 
 New Dosage Tables. 280. 
 Melaxuma of the Walnut, "Juglans 
 
 regia." 281. 
 Citrus Diseases of Florida and Cuba 
 
 Compared with Those of California. 282. 
 Size Grade for Ripe Olives. 
 
 The Calibration of the Leakage Meter. 283. 
 
 Cotton Rot of Lemons in California. 284. 
 
 A Spotting of Citrus Fruits Due to the 285. 
 
 Action of Oil Liberated from the Rind. 286. 
 
 Experiments with Stocks for Citrus. 287. 
 Growing and Grafting Olive Seedlings. 
 
 CIRCULARS 
 No. 
 152. 
 
 A Comparison of Annual Cropping, Bi- 
 ennial Cropping, and Green Manures 
 on the Yield of Wheat. 
 
 Feeding Dairy Calves in California. 
 
 Commercial Fertilizers. 
 
 Preliminary Report on Kearney Vine- 
 yard Experimental Drain. 
 
 The Common Honey Bee as an Agent 
 in Prune Pollination. 
 
 The Cultivation of Belladonna in Cali- 
 fornia. 
 
 The Pomegranate. 
 
 Sudan Grass. 
 
 Grain Sorghums. 
 
 Irrigation of Rice in California. 
 
 Irrigation of Alfalfa in the Sacramento 
 Valley. 
 
 Control of the Pocket Gophers in Cali- 
 fornia. 
 
 Trials with California Silage Crops for 
 Dairy Cows. 
 
 The Olive Insects of California. 
 
 Irrigation of Alfalfa in Imperial Valley. 
 
 The Milch Goat in California. 
 
 Commercial Fertilizers. 
 
 Vinegar from Waste Fruits. 
 
 Correspondence Courses in Agriculture. 
 
 Increasing the Dutv of Water. 
 
 Grafting Vinifera Vineyards. 
 
 Some Things the Prospective Settler 
 Should Know. 
 
 Alfalfa Silage for Fattening Steers. 
 
 Spraying for the Grape Leaf Hopper. 
 
 House Fumigation. 
 
 Insecticide Formulas. 
 
 The Control of Citrus Insects. 
 
 Spraying for Control of Walnut Aphis. 
 
 County Farm Adviser. 
 
 Control of Raisin Insects. 
 
 Official Tests of Dairy Cows. 
 
 Melilotus Indica. 
 
 Wood Decay in Orchard Trees. 
 
 The SUo in California Agriculture. 
 
 The Generation of Hvdrocyanic Acid 
 Gas in Fumigation by Portable Ma- 
 chines. 
 
 The Praotical Application of Improved 
 Methods of Fermentation in Califor- 
 nia Wineries during 1913 and 1914. 
 
 Standard Insecticides and Fungicides 
 versus Secret Preparations. 
 
 Practical and Inexpensive Poultry Ap- 
 pliances. 
 
 Control of Grasshoppers in Imperial 
 Valley. 
 
 Oidium or Powderv Mildew of the Vine. 
 
 SueerrstionR to Poultrymen concerning 
 Chicken Pox. 
 
 Tomato Crowing in California. 
 
 "Lungworms." 
 
 Round Worms in Poultry. 
 
 Feeding and Management of TTogs. 
 
 Some Observations on the Bulk Hand- 
 ling of Grain in California. 
 
 Announcement of the California State 
 Dairy Cow Competition, 1916-18. 
 
 Irrigation Practice in Growing Small 
 Fruits in California. 
 
 Bovine Tuberculosis. 
 
 How to Operate an Incubator. 
 
 Control of the Pear Scab. 
 
 Home and Farm Canning. 
 
 Lettuce Growing in California. 
 
 161. Potatoes in California. 
 
 162. White Diarrhoea and Coccidiosis of 
 
 Chicks. 
 Small Fruit Culture in California. 
 Fundamentals of Sugar Beet under 
 
 California Conditions. 
 The County Farm Bureau. 
 
 167. Feeding Stuffs of Minor Importance. 
 
 168. Spraying for the Control of Wild Morn- 
 ing-Glory within the Fog Belt. 
 
 1918 Grain Crop. 
 
 Fertilizing California Soils for the 1918 
 
 Crop. 
 The Fertilization of Citrus. 
 Wheat Culture. 
 The Construction of the Wood-Hoop 
 
 Silo. 
 Farm Drainage Methods. 
 Progress Report on the Marketing and 
 
 Distribution of Milk. 
 Hog Cholera Prevention and the 
 
 Serum Treatment. 
 Grain Sorghum Seed. 
 The Packing of Apples in California. 
 
 153. 
 
 154. 
 
 155. 
 156. 
 157. 
 158. 
 160. 
 
 164. 
 165. 
 
 166. 
 
 169. 
 170. 
 
 171. 
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 174. 
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 176. 
 
 177. 
 178.