UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA CIRCULAR 319 October, 1930 PASTEURIZING MILK FOR CALF FEEDING C. L. ROADHOUSEi and E. L. PERRY 2 HEIFERS IN ALAMEDA COUNTY RAISED ON PASTEURIZED MILK The importance to dairymen of raising calves from high-producing cows as a satisfactory and economical means of maintaining and improving milk production has been emphasized from the very begin- ning of dairy-herd improvement. It has also been pointed out by dairy leaders in the state that thousands of dairy cows during the past year have been purchased in other states and shipped to California to supply the demand for disease-free cattle, particularly in those sections where market milk is produced for the larger cities. It is easy to recognize in this situa- tion an economic loss to the dairymen of California, and this and 1 Professor of Dairy Industry and Dairy Technologist in the Experiment Station. 2 Assistant Professor of Agricultural Engineering and Assistant Agricultural Engineer in the Experiment Station. 2 University of California — Experiment Station other publications 3 of the College of Agriculture are prepared for the purpose of giving information which may be useful to dairymen interested in raising calves and protecting them from disease. It is entirely possible and practical to raise calves on pasteurized milk. The Hansen and Orloff Dairy at Pleasanton, California, has been very successful in raising calves in this way. Of the first three hundred calves raised on pasteurized milk there were only eight reactors from the first test, made when the calves were two months old. There was Fig. 1. — Month-old calves being raised on pasteurized milk. Pasteurized whole milk is fed during the first month, followed by the use of pasteurized skim milk, calf meal, and hay. one reactor at the second test made when the calves were five to six months old. These results were secured when the calves were left with the mother one day and then fed pasteurized milk from a non- tested herd and kept separated on the same premises. At five, to six months of age the calves were removed to an isolated pasture. 3 Mead, S. W. Feeding and management of dairy calves in California. Cali- fornia Agr. Exp. Sta. Bui. 478:1-31, 1929. Haring, C. M., and J. Traum. Bovine tuberculosis. California Agr. Ext. Ser. Cir. 21:1-27. 1929. Haring, C. M. Rearing dairy heifers free from tuberculosis and abortion disease. California Agr. Ext. Ser. Cir. 33:1-19. 1928. Hayes, F. M. Bang's disease. California Agr. Ext. Ser. Cir. 44:1-24. 1930. Cm. 319] Pasteurizing Milk for Calf Feeding DESTRUCTION OF DISEASE-PRODUCING BACTERIA The destruction of disease-producing bacteria which may have gained entrance to the milk is accomplished by heating the milk in the process known as pasteurization. The length of time that the milk is heated should determine the temperature necessary to destroy such bacteria. When milk is heated to a temperature of 160° Fahrenheit and held at that temperature for one minute it is to be expected that all bacteria causing tuberculosis and infectious abortion will be killed. However, a lower temperature will destroy the bacteria causing these diseases if the mill?: is allowed to remain hot for a longer time. It is recognized that a temperature of 140° Fahr. maintained for 20 minutes will make milk safe for human or animal consumption, but there is always an opportunity for error in the amount of heat applied and in the length of time the milk remains hot, and for this reason the California State Dairy Law, as a minimum requirement, specifies that milk pasteurized and sold for human consumption shall be heated to a temperature between 140° and 145° Fahr. and held between these limits for at least 30 minutes. In pasteurizing mill?: for calf feeding it is recommended that a higher temperature of heating be used than is customary in pasteuriz- ing milk for human consumption. There are several reasons for this. On the farm the pasteurizing will frequently be done by an operator less experienced than the man usually employed in commercial pas- teurizing plants. He will have other duties to perform and less time to give to checking carefully the temperature of heating and time of holding. The room in which the milk is heated in winter will probably be colder than the heated building in which milk is usually pasteurized commercially, and this may cause the milk to cool more rapidly and thus fail to kill all of the disease-producing bacteria. Milk should be heated to a temperature of 170° Fahr. when pas- teurized in a vat for calf feeding. This temperature is considerably above the minimum required to destroy disease-producing bacteria, but the higher temperature overcomes the possibility of mistakes. The milk should be held in the container in which it is heated for at least 30 minutes, allowed to cool in the can or feeding pails to 100° Fahr., and fed to the calves immediately. If a portion of the milk is to be kept several hours until the next feeding, that portion should be cooled to as low a temperature as possible, kept cold and covered to avoid contamination from flies and dust, and then warmed just 4 University of California — Experiment Station before feeding-. In the use of some types of pasteurizing" equipment a temperature lower than 170° Fahr. may be safely used. This pro- cedure will be described in the directions given for the use of certain pasteurizing equipment recommended in this bulletin. EQUIPMENT WHICH MAY BE USED FOR PASTEURIZING MILK FOR CALF FEEDING Many dairymen milk only a few cows and consequently have only a few calves to feed. The equipment to be used for pasteurizing a small amount of milk is likely to be different from that recommended for dairymen having larger herds. It is to be emphasized that any sanitary equipment which will heat the milk to the proper tempera- ture and permit all of the milk to be held at a temperature above 160° Fahr. for 20 minutes may be considered satisfactory for pas- teurizing milk for the feeding of calves. It is not satisfactory to heat milk by the direct flame for two reasons : the milk is not uniformly heated unless continuously agitated ; and that portion which is in contact with the bottom of the container burns on to the surface, causing difficult cleaning. The California Dairy Law requires that every dairyman selling milk or cream shall sterilize all dairy apparatus coming in contact with the milk. It has been demonstrated in experiments described in this circular that certain sterilizing equipment commonly used by dairymen for sterilizing utensils may also be used for pasteurizing milk for calf feeding. When pasteurizing milk by this method the heat was produced in the farm type of sterilizing equipment or by steam from a steam boiler. The Chief of the Bureau of Dairy Control, State Department of Agriculture, has stated that under controlled conditions there would be no objection to pasteurizing milk in the sterilizer at the same time the dairy equipmnt is being heated, but if the milk is carelessly handled on the ranch, and some of the product is spilled in the sterilizer, unsatisfactory conditions will result. Where market milk is produced, it would be better to keep the operation of pasteurization separate from the sterilization of dairy utensils. The dairyman should have this in mind in the selection of the equipment used for pasteuriz- ing milk for calf feeding. Cir. 319] Pasteurizing Milk for Calf Feeding PASTEURIZING MILK IN THE KEROSENE-HEATED GALVANIZED TANK STERILIZER The kerosene-heated galvanized dairy-equipment sterilizer has been in use on many dairy farms for the regular sterilization of dairy apparatus. This sterilizer is shown in figure 2, and consists of a galvanized-iron tank with a cover and a galvanized-iron jacket sur- HI • ■ • ;'kl'^'^». ; HJ^E& ' wHllte,!'.!.^^ : -^B^r^^^Ht Fig. 2. — Kerosene-heated galvanized tank sterilizer. rounding the sides and bottom of the body of the tank. Water, sufficient to cover the bottom, is placed in the tank and the heat for sterilization is produced by boiling the water by means of a kerosene burner located in the jacket beneath the tank. The kerosene fuel is supplied to the burner from an elevated container. The heat from the burner flame, passing across the bottom and up the sides of the inner tank, raises the temperature of the water to boiling. In this way the steam which forms in the tank is superheated. 6 University of California — Experiment Station This apparatus may be used for pasteurizing" milk in a 10-gallon can. The can of milk with lid removed, may be placed into the sterilizer during the course of the regular sterilization of dairy equipment. In the three experiments carried out with this equipment, 80.3 pounds (9% gallons) of milk in a 10-gallon can at a temperature of 70° Fahr. were placed into the sterilizer containing 42 pounds (about 5 gallons) of water at 67° Fahr. Sixty pounds of dairy equipment, consisting of a milk cooler, a supply vat, an empty milk can and a milk pail, were placed in the sterilizer for sterilization at the same time the milk was being pasteurized. The flame was then started and it required from 28 to 36 minutes for the steam in the tank to reach 212° Fahr. The utensils likewise reached this temperature. The flame was then turned lower and this temperature maintained for 25 minutes, after which time the tem- perature of the milk ranged between 160° and 175° Fahr. The kerosene-heated sterilizer gave considerable variation in results as shown above. The flame apparently was not constant in heating properties. Variations may be due to variations in the temperature of the surrounding air or to the accumulation of soot on the bottom of the sterilizer, which retards heating. This is one of the most unsatisfactory conditions in the use of the kerosene-heated sterilizer. The minimum temperature to which the milk was heated was suffici- ently high, however, to make this method safe in spite of such variation. In experiments conducted by Farrall, 4 the cost of sterilizing 60 pounds of dairy equipment in this sterilizer with kerosene costing 16 cents per gallon averaged 3.6 cents per sterilization. In the experi- ments herein reported where 80.3 pounds of milk in a 10-gallon can were placed in the sterilizer with 60 pounds of dairy equipment, 3.1 pints of kerosene, costing- 5 cents, were used. On this basis, the cost of pasteurizing 80.3 pounds of milk over that of sterilizing the equipment was 1.4 cents. It is practical and entirely satisfactory to pasteurize milk for the feeding of calves by placing a 10-gallon can of milk in a kerosene- heated sterilizer and heating the milk at the same time the equipment is being sterilized. When the sterilizer was heated to a temperature of 212° Fahr. and held at that temperature for 20 minutes the milk in the can reached a temperature ranging from 160° to 175° Fahr. If this milk is allowed to stand in the can for half an hour it may then be cooled to 100° Fahr. for feeding immediately. If the milk is 4 Farrall, A. W. Operating characteristics of oil heated steam type sterilizers. Agr. Engineering, 8:237-240. 1927. Cir. 319] Pasteurizing Milk for Calf Feeding 7 to be held several hours until the next feeding it is considered desirable to cool the milk to a temperature as low as possible by standing the can in cold running water. This method of heating the milk gave the lowest cost of the various methods tested. Steps in Pasteurizing Milk in the Kerosene-heated Sterilizer — 1. Remove soot from bottom of sterilizer tank in case of an accumulation, and clean openings of burner jets. 2. Add water to sterilizer tank to height of overflow pipe when in lower notch. 3. Place can of milk and utensils in sterilizer. 4. Open petcock at the bottom of the fuel line and draw off kerosene into small can to remove trapped air. 5. Saturate the lighter with alcohol or kerosene, ignite it and place it directly under the burner. 6. When pipe is hot open the fuel valve slightly and let kerosene pass into the hot pipe, where it should volatilize and the vapor ignite. 7. Heat the sterilizer until the steam in the tank reaches 212° Fahr. 8. Turn down fuel valve slightly and hold heat at 212° Fahr. for 25 minutes. 9. Shut off fuel valve. 10. Remove cover of sterilizer as soon as flame is turned off to permit utensils to dry. 11. Cool milk to 100° Fahr. before feeding. The kerosene-heated sterilizer may be used for pasteurizing several cans of milk when equipment is not being sterilized at the same time. The smaller size of sterilizer will accommodate four 10-gallon cans. The average cost of pasteurizing 40 gallons of skim milk by this method was 10.4 cents, or 0.26 cents per gallon. PASTEURIZING MILK IN THE ELECTRICALLY HEATED GALVANIZED TANK STERILIZER In recent years the electrically heated galvanized tank sterilizer has come into use on some dairy farms. This equipment may be used for pasteurizing milk for calves by the method described for the kerosene-heated sterilizer. The time required for heating with elec- tricity is greater because of the slower application of heat. One type of electrically heated sterilizer is shown in figure 3, and consists of a galvanized-iron tank with a cover and a galvanized-iron 8 University of California — Experiment Station jacket surrouunding the sides and bottom of the body of the tank. The heat for sterilization is supplied from a 5-kw. electric immersion heating element, which is located in a depression in the bottom of the tank. Sufficient water is placed in the tank to insure that the heating element will remain submerged during the sterilizing process. This apparatus may be used for pasteurizing milk in a 10-gallon can by placing the can containing the milk in the sterilizer during the Fig. 3. — A type of electric dairy-equipment sterilizer used on some dairy farms. course of the regular equipment-sterilizing process, the same procedure being followed as was described for the use of the kerosene-heated sterilizer. In the experiments conducted by Farrall and Moses 5 the cost of sterilizing 60 pounds of dairy equipment in the electric sterilizer, with electric energy costing 2 cents per kilowatt hour, averaged between 4.8 and 5.8 cents per sterilization. If milk is pasteurized separately from the sterilization of equipment the cost would be between 11.5 and 13.4 cents for 80.3 pounds of milk. In the experiments herein s Farrall, A. W., and B. D. Moses. Operating characteristics of electrically heated steam type sterilizers. Agr. Engineering 8:273-277. 1927. Cir. 319] Pasteurizing Milk for Calf Feeding reported, where 80.3 pounds of skim milk in a, 10-gallon can were placed in the sterilizer with 60 pounds of dairy equipment, the average additional cost for pasteurization varied from 6.7 to 7.6 cents for 80.3 pounds of skim milk. In the experiments in pasteurizing milk in the electrically heated sterilizer, a heating element of 5 kw. was used. If a smaller heating element were used, the time required for pasteurization would be undesirably prolonged and the loss of energy increased. It is recom- mended that the 5 kw. heating element be used. Fig. 4. — Galvanized tank sterilizer heated with steam from a steam boiler. GALVANIZED TANK HEATED WITH STEAM FROM BOILER On many dairy farms where milk is produced for city supply, a covered galvanized tank is used for sterilizing dairy equipment (fig. 4). Steam for heating the utensils is supplied from a small upright or horizontal boiler. Experiments were undertaken to determine the cost of pasteurizing a 10-gallon can of skim milk at the same time the regular sterilization of equipment was carried out. The steam was turned on full until 10 University of California — Experiment Station the temperature in the tank reached 200° Fahr., which required 15 minutes. The steam valve was partially closed to maintain the tem- perature in the tank at 200° Fahr. for 20 minutes. The cover was then raised to allow steam to escape and equipment to dry. The milk was stirred and the temperature was found to be 173° Fahr. The average weight of steam condensed in the tank was 18.8 pounds, and the cost of fuel for pasteurizing the skim milk and sterilizing the utensils together was 3 cents. If the boiler is used for only one operation of the sterilizer for pasteurizing milk and sterilizing utensils, the cost of fuel required for raising the steam in the boiler should be added to the cost of 3 cents for fuel used during operation, which would bring the total cost for fuel to 10 cents, when * stove tops' costing 7 cents per gallon is the fuel used. When the steam pressure was high and the temperature in the tank reached 200° Fahr. in 10 minutes and was then held for 20 minutes, the temperature of the milk was 154° Fahr. From this it is apparent that the speed of heating the tank influences the final temperature of the milk, and care should be used in regulating the process to secure uniform results. Steps in Pasteurizing Milk in the Galvanized Tank with Steam Supplied from Boiler — 1. Place can of mill?: with utensils in sterilizer. 2. Close cover and turn on steam. 3. Regulate flow of steam to heat tank to 200° Fahr. in 15 minutes. 4. Close steam valve sufficiently to maintain temperature at 200° Fahr. for 20 minutes. 5. Turn off steam and raise cover to permit utensils to dry. 6. Stir milk and check actual temperature with a standard dairy thermometer (fig. 9A). 7. Cool milk by standing can in cold water. PASTEURIZING MILK IN lO-GALLON CAN IMMERSED IN HOT WATER Where only a small quantity of milk is required for feeding it may be pasteurized also in a 10-gallon can immersed in hot water. A wooden tub such as is used for packing icecream cans of 5-gallon capacity may be used. This type of tube is very satisfactory because of its size; it accommodates the can of mill?: and requires the use of only a small amount of water. The wood serves as an insulator, avoids excessive loss of heat from the water and maintains the temperature during the holding period after the milk has been heated. The tub Cir. 319] Pasteurizing Milk for Calf Feeding 11 is also inexpensive and readily obtainable from dairy-equipment distributors. In conducting" the experiment on this equipment the water placed in this tub was heated by passing steam from a boiler through a hose connected with a galvanized-iron pipe which carried the steam to the bottom of the tub. The steam was distributed at the bottom of the tub through a pipe cross constructed with four capped nipples screwed Fig. 5. — (A) Ten-gallon can containing milk to be pasteurized. (B) Ice- cream packer containing water. (C) Steam-distributing pipe. (D) Steam boiler. into a galvanized-iron cross. Openings were made in the bottom side of the pipes with a hacksaw to allow for an even distribution of the steam. This apparatus, together with a vertical boiler of 2 horse- power capacity, is shown in figure 5. In preparation for the pasteurization of the milk the steam-dis- tributing pipe was placed in the tub. The can containing the milk was then placed into the tub with the bottom resting upon the steam- distributing pipes, which permitted the uniform heating of the bottom and side surfaces. Thirty pounds of water was used in the tub, which, with the condensed steam developed during heating, brought the water 12 University of California — Experiment Station in the tub to the level of the 80.3 pounds of milk contained in the can. The steam valve from the boiler was then partially opened and the steam allowed to pass into the water in the tub, thus supplying the heat for pasteurization. When the temperature of the water reached 175° Fahr., requiring an average of 9 minutes, the valve was closed and then opened slightly to maintain the temperature of the water at 175° Fahr. for an average of 16 minutes. The temperature of the milk in the can after stirring was then 160° Fahr. The milk was left standing in the hot water for 30 minutes, which maintained the temperature at 160° Fahr. ; it was then cooled to feeding temperature. The cost of pasteurizing by this method was calculated from the amount of steam condensed in the water, which varied from 10.2 to 11.4 pounds. Calculating the results on the basis of the probable efficiency of the average farm boiler, gives a fuel cost of 1.75 cents for heating 10 gallons of milk from 70° to 160° Fahr. in pasteurizing, when 'stove tops' fuel costing 7 cents per gallon is used. The 'firing- up' of the boiler required 1 gallon of fuel costing 7 cents, but this cost has not been added to the cost of pasteurization, since this method of heating milk assumes that a boiler is available and being used for other purposes, such as sterilization of equipment, When milk is pasteurized with this equipment during the winter months, the colder temperature of the air and milk would require the use of more steam than during the summer months. A canvas cover placed over the tub while the milk is hot is a means of reducing the loss of heat and the cost of pasteurization. It is practical and entirely satisfactory to pasteurize milk for the feeding of calves by placing a 10-gallon can of milk in water in a wooden tub and heating the water with steam as a means of uniformly heating the milk. If water is heated with steam to 175° Fahr. and maintained at that temperature for 16 minutes, the temperature of the milk in the can will reach 160° Fahr. This result varies somewhat according to the temperature of the room, initial temperature of the milk, and the rapidity of heating the water. The can containing the milk should be left standing in the water for 30 minutets. During cold weather the can should be covered with a canvas to reduce the loss of heat. Steps in Pasteurizing Milk by Immersing Cans in Hot Water — 1. Place milk in 10-gallon can to reach nearly to the top. 2. Place steam-distributing pipe in tub. 3. Place can of milk on top of steam-distributing pipes. 4. Add water to tub to the same level as the milk in the can. Cir. 319] Pasteurizing Milk for Calf Feeding 13 5. Turn steam into distributing' pipe and heat water to 175° Fahr. 6. Close steam valve and then open it slightly to maintain tem- perature of 160° Fahr. 7. Place canvas cover over tub and hold can in water for 30 minutes. 8. Remove milk from tub and cool to 100° Fahr. before feeding. PASTEURIZING WITH STEAM PASSED DIRECTLY INTO MILK The California Dairy Law requires that milk to be returned from dairy plants to the farm for animal feeding be pasteurized before it is removed from the plant, It is common practice to pasteurize such milk by injecting steam directly into the milk. This method requires little additional equipment if a steam boiler is available. It is effective, easily performed, and relatively inexpensive. In heating milk in 10-gallon cans by steam from a boiler by means of a steam hose, the amount of steam required to raise the temperature of 10 gallons of skim milk from 70° to 160° Fahr. averaged 7.8 pounds. The amount of steam required varies with the steam pressure and the amount of moisture carried over with the steam. The fuel cost at 7 cents per gallon of 'stove tops' was 1.2 cents for 10 gallons of milk. This method is not recommended because of the possible slightly injurious effect of direct steam upon the feeding value of the milk, dilution of the milk with condensed steam, and the possible addition of chemicals from the boiler. The question has been raised as to the effect of material contained in the boiler water on the wholesomeness of the milk when heated by direct steam. This will depend upon the kind and amount of material which may be carried over into the milk by the steam used for heating. The substances which may be carried in slight amounts by wet steam are carbonates, sulfates, phosphates, hydroxides and chlorides of sodium, calcium, and magnesium. Some of these may enter the boiler with hard water, while others may be introduced with boiler compounds. Additional materials such as tannates and silicates may be found in boiler compounds, as well as filler material, the analysis of which is often not known by the user. The amount of materials which may be carried over into milk heated for pasteurization will depend upon the amount of moisture in the steam, and the amount of solids in the boiler water. These in turn depend on the hardness of the water, the kind of compounds used in the boiler water, the amount and the method of use. The type and size of the boiler, the frequency of blowing down the boiler, the height 14 University of California — Experiment Station of water level, and the rate at which steam is used from the boiler also influence the amount of solids carried into the milk from the boiler. When there is an extreme concentration of solid materials in the boiler and excessive moisture content in the steam, the maximum amount which might be added to milk with steam during pasteuri- zation would be les than *4 ounce in 10 gallons of milk. With normal operation the amount will not exceed y 100 of an ounce. When boilers are operated under most favorable conditions, even when boiler compounds are used, it can be expected that not more than %oo ounce of solid material will be added to 10 gallons of milk as a result of passing steam directly into it. Although this small amount of foreign material may not be injurious to the health of calves con- suming such milk, this condition should be reckoned with when con- sidering the pasteurization of milk with steam passed into it directly from the boiler. THE VERTICAL PASTEURIZER Large quantities of milk can be pasteurized best by the use of standard dairy-plant equipment. The vertical pasteurizer described below and the horizontal-coil pasteurizer described subsequently are two types of equipment well adapted to this purpose. The vertical pasteurizer studied was a 50-gallon 'starter can,' which is commonly used in dairy plants for preparation of starter used in cheese and butter manufacture, as shown in figure 6. It con- sists of a vertical cylindrical tinned-copper container, surrounded by a water jacket which is used for heating and cooling. Heating is accomplished by passing live steam into the jacket or by passing steam into the jacket which is partially filled with water. Agitation is accomplished by a vertical coil or paddle suspended from a vertical bearing at the top of the can. After pasteurization of the milk it is drawn off through an outlet pipe closed by a sanitary gate. In the experiments on pasteurizing milk in the starter can, the apparatus was filled with 394 pounds of skim mill?:, the temperature of which was 70° Fahr. The water jacket was then filled to the over- flow level. Steam was turned on to maintain a normal temperature rise of about 3y 2 ° Fahr. per minute. The steam passing into the water condensed, displacing an equal amount of water, which was collected at the overflow pipe, and weighed to determine the amount of steam used in heating the milk. The temperature of the milk in the vat was determined periodically with a chemical thermometer. When the temperature of the water in the jacket reached 180° Fahr. the steam Cm. 319] Pasteurizing Milk for Calf Feeding 15 Fig. 6. — The vertical pasteurizer. The milk in the outlet pipe A does not heat satisfactorily. It should be drawn off and returned to the vat when pasteuri- zation temperature is reached. 16 University of California — Experiment Station rate was reduced until the temperature of the milk reached 164° Fahr. The steam was then shut off. The heat of the water in the jacket carried the milk temperature to 170° Fahr. as is recommended. After maintaining this temperature for 30 minutes, water at 70° Fahr. was circulated through the jacket until the milk was cooled to 100° Fahr. Heating 394 pounds of skim milk from a temperature of 70° Fahr. to a temperature of 170° Fahr. in the 'starter can' required the equivalent of 67 pounds of steam at 15 pounds per square inch gauge pressure. The time used for heating varied from 32 to 40 minutes. This rate of heating was equivalent to 3.5 to 4.25 boiler horse-power. The cost of fuel for pasteurizing milk by this method varies with the type and size of boiler used to furnish steam, insulation on the pasteurizer jacket, and other conditions affecting efficiency. Calcu- lating the results on the basis of the probable efficiency of the average farm boiler gives a fuel cost of 11 cents for heating 50 gallons of skim milk from 70° to 170° Fahr. when 'stove tops' oil costing 7 cents per gallon is used. This does not include the fuel used to develop the steam pressure in the boiler, since it is assumed that when this method of heating milk is used, a boiler is available and being used for other purposes, such as sterilization of equipment. Milk may be readily pasteurized in the 'starter can' when heated with steam from a boiler where the quantity of milk to be pasteurized daily warrants the use of this larger equipment. The attention required during operation is slight, so that other chores may be carried on at the same time. Steps in Pasteurizing Milk in the 'Starter Can' — 1. Place milk in starter can. 2. Turn water into the jacket until partly filled. 3. Start agitator. 4. Turn on steam until water in jacket reaches 180° Fahr. 5. Reduce steam rate to maintain jacket temperature at 180° Fahr. 6. Shut off steam when temperature is high enough to carry milk up to 170° Fahr. 7. Draw off cold milk in outlet pipe immediately and pour into vat. 8. Place cover on vat to permit foam to heat to pasteurizing tem- perature. 9. Hold milk covered in the vat for 30 minutes. 10. Circulate cold water through the jacket to cool milk to 100° Fahr. and draw off milk for feeding. Cir. 319] Pasteurizing Milk for Calf Feeding 17 PASTEURIZING MILK IN THE HORIZONTAL-COIL PASTEURIZER The horizontal-coil pasteurizer studied was a 75-gallon horizontal vat, with insulated sides and cover as shown in figure 7. Heating and cooling in this type of equipment is effected by circulating hot or cold water or brine through a rotating horizontal coil which passes Fig. 7. — Vat pasteurizer with horizontal coil. Kecording thermometer A provides a means of checking temperatures and 'holding time' of milk. through packing glands in each end of the vat. The steam, water, and brine pipes are connected to the inlet end of the coil by a stuffing box. When heating, steam is injected through a mixing nozzle to raise the temperature of the water, which it draws from the reservoir at the discharge end of the coil, and recirculates through the coil. When cooling with water, the water passes through the coil and is discharged 18 University of California — Experiment Station from the reservoir. A pump must be provided for recirculation if brine is used for further cooling. When pasteurization is carried out by employees who are not especially interested in protecting the health of the animals, it is considered desirable for the owner to install a recording thermometer such as is shown at A in figure 7. By the use of this instrument a separate record sheet (fig. 8) may be prepared for each day's operation. The temperature is shown by Fig. 8. — Becording-thermometer chart showing temperature of pasteurization of milk and sterilizing of vat. the distance of the heavy line from the center of the chart, while the time of holding is indicated by the radiating lines. A study of the pasteurization record in figure 8 shows the initial temperature of the milk, the temperature to which the milk was heated (A), the time of holding the milk hot (A-A), and the temperature to which the milk was cooled. At B in the figure is shown the tempera- ture at which the milk was drawn from the vat for immediate feeding, and at C the temperature to which the remainder of the milk was cooled to be held until the next feeding. D represents the temperature at which the vat was sterilized after the milk was removed. It is important to check recording thermometers frequently by means of a hand thermometer to make sure of their accuracy. A Cie. 319] Pasteurizing Milk for Calf Feeding 19 small hand thermometer, such as is shown in figure 9A, or a long stem thermometer, figure 9B, may be used for checking the accuracy of the recording thermometer. Fig. 9. — Types of hand thermometers that may be used for checking milk- pasteurization temperatures and accuracy of recording thermometers. In the experiments on pasteurizing milk in the horizontal-coil pasteurizer the pasteurizer was filled with 640 pounds of milk at 70° Fahr. and the coil and water tank in the end of the pasteurizer were filled with water to the overflow level. Steam was turned on to maintain a temperature rise of 2%° Fahr. per minute. The steam 20 University of California — Experiment Station passing into the water condensed, displacing an equal amount of water at the overflow pipe, which was collected and weighed to determine the amount of steam used for heating the milk. The temperature of the milk in the vat was determined periodically with a chemical ther- mometer. When the temperature of the milk reached 169° Fahr. the steam was shut off, and heat in the coil carried the milk temperature to 170° Fahr. After maintaining this temperature for 30 minutes, water at 70° Fahr. was circulated through the coil, and the milk cooled rapidly to 100° Fahr. Heating 640 pounds of skim milk from a temperature of 70° Fahr. up to a temperature of 170° Fahr. in the horizontal-coil pasteurizer required the equivalent of 75 pounds of steam at 15 pounds per square inch gauge pressure. The time required for heating varied from 36 to 37 minutes. This rate of heating was equivalent to 4% boiler horsepower. Cooling to 100° Fahr. was accomplished rapidly when water at 70° Fahr. was circulated through the coil. Calculating the results on the basis of the probable efficiency of the average farm boiler gives a fuel cost of 12.3 cents for heating 75 gallons of skim milk from 70° Fahr. to 170° Fahr. if 'stove tops' costing 7 cents per gallon is used. Milk may be readily pasteurized in the horizontal-coil pasteurizer when heated with steam from a boiler, where the quantity of milk to be handled warrants the use of this larger equipment. Milk is more readily handled with this equipment that with the vertical ' starter can' because it is not necessary to lift it so high when filling. Little attention is required during the operation of this equipment. Con- siderably less steam is required per gallon in pasteurizing milk with this equipment than with the 'starter can' because the vat is insulated against loss of heat. Steps in Pasteurizing in the Horizontal-Coil Pasteurizer — 1. Place milk in vat. 2. Place overflow stand pipe in reservoir at the end of pasteurizer. 3. Turn water into coil and reservoir until partly filled. 4. Start coil revolving. 5. Turn on steam to give temperature rise of about 3° Fahr. per minute. 6. Shut off steam when milk reaches 170° Fahr. 7. Place cover on vat to permit foam to heat to pasteurizing tem- perature. 8. Maintain temperature of milk in the vat at 170° Fahr. for 30 minutes. Cm. 319] Pasteurizing Milk for Calf Feeding 21 9. Remove overflow stand pipe and circulate cold water through the coil to cool milk. 10. Milk for immediate feeding should be drawn off at 100° Fahr. 11. Milk to be held for later feeding should be cooled as low as possible and held in the vat until ready for use. DANGER FROM IMPROPER USE OF VAT PASTEURIZERS When using the vat pasteurizer for heating and holding the milk there is great danger that the milk in the outlet pipe (fig. 6 A) may not be heated high enough to destroy disease-producing bacteria. This milk, when drawn from the vat, mixes with the pasteurized milk and may add the germs of bovine tuberculosis or infectious abortion to the milk and render the pasteurizing process ineffective. Unpublished experiments by the writers conducted at this Experi- ment Station with a horizontal-coil pasteurizer have shown that it was necessary to heat the milk in the vat to a temperature of 170° Fahr. and hold it at that temperature for 30 minutes in order to have the milk in the outlet valve reach a temperature of 142° Fahr. for 20 minutes. This is an important point where either the vertical or horizontal-coil pasteurizers are used. Because of the difficulty of properly heating the milk in the outlet pipe it is recommended that when vat pasteurizers are used for heating milk the temperature should reach 170° Fahr. and be maintained for 30 minutes. As a precaution to assure the proper heating of the milk in the outlet pipe, it is desirable practice to draw off a gallon of milk as soon as the temperature in the vat reaches 170° Fahr. and pour it back into the vat. This procedure replaces the colder milk in the pipe with hot milk from the vat, and thereby reduces the risk of failure. Milk cannot be safely pasteurized when outlet pipe leads from the bottom of the vat. Experiments carried out by the writers have shown that it is not possible to properly pasteurize milk in a vat when the outlet pipe leads from the bottom of the container. Figure 10 shows a homemade apparatus of this type (A) in which the outlet pipe (B) contained cold milk at the beginning of the heating process. When the milk in the vat was heated to 170° Fahr. and held for 30 minutes the milk in the outlet pipe reached a temperature of only 98° Fahr. This temperature would not destroy the bacteria in the milk contained in the outlet pipe and they would mix with the pas- teurized mill?: when it was drawn off and infect the entire batch. 22 University of California — Experiment Station Fig. 10. — Section of homemade type pasteurizing tank A, with unsatisfactory milk outlet pipe B, leading from bottom of tank. The milk remains cold in the outlet pipe throughout pasteurization. Insulated wall of vat VAT Wide flaring entrance to outlet pipe Sanitary outlet valve Short outlet pipe Fig. 11. — Section of pasteurizer with satisfactory enlarged V-shaped opening to outlet pipe and outlet valve placed close to vat. Cir. 319] Pasteurizing Milk for Calf Feeding 23 IMPROVED VAT PASTEURIZERS Some dairy machinery manufacturers have recently improved upon the construction of vat pasteurizers by changing" the shape of the outlet opening and placing the outlet valve close to the end of the vat as shown in figure 11. In a horizontal-coil pasteurizer with this construction the coil circulates the milk in the outlet pipe and brings its temperature to a point near that of the milk in the vat. With the use of this improved type of vat all parts of the milk can be considered to be properly pasteurized if the milk in the vat is heated to 160° Fahr. and held at that temperature for 30 minutes. STEAM BOILERS FOR PASTEURIZING There are three types of boilers well adapted for farm use : the vertical non-tubular boiler, the vertical fire-tube boiler, and the horizontal return tubular five-box boiler. The horsepower rating of a boiler is determined by the area of heating surface exposed for transfer of heat from the hot flue guses to the water and steam. Manufacturers allow 12 square feet of heat- ing surface per boiler horsepower. Boilers will convert approximately 30 pounds of water into steam each hour for each horsepower of rated capacity. In selecting the size of the boiler to be used, one should be governed by the amount of heating- to b# done, and the time required. Each pound of steam will provide heat for pasteurizing 1 y 2 to iy± gallons of milk. For example, heating 50 gallons of milk in 30 minutes to a pasteurizing temperature of 170° Fahr. will require approximately 50 pounds of steam in 30 minutes. A 3-horsepower boiler will furnish 45 pounds of steam in 30 minutes, and will be satisfactory for the example described. The boiler selected must be large enough to furnish steam at the rate required, or it will unduly retard the work. However, oversize boilers are uneconomical because of the greater loss of heat from their outside surfaces. Many boilers on the farm are used for a few hours only each day and the fuel required to heat the boiler and raise steam is frequently as much as that used in the work done. 24 University of California — Experiment Station ACKNOWLEDGMENTS The authors wish to acknowledge the suggestions given by Dr. C. M. Haring of the Veterinary Science Division and the use of equip- ment and photographs furnished by him; assistance given by Dr. G. K. Cooke of the Berkeley Health Department, and suggestions from Mr. G. E. Gordon of the Agricultural Extension Service. Appreciation is also expressed for the assistance of Mr. S. F. Aichholz and Mr. M. J. Fechter in carrying out the details of some of the experiments. 20m-10,'30