292 CITY MILK SUPPLY 



The tank is filled with water of the desired temperature and the wheels 

 are set in motion by a drive gear at the end of the tank. Thus the cans 

 revolve and the milk is stirred by the paddle. When the proper time has 

 elapsed the milk is poured from the cans over a cooler. 



Type 8. For pasteurizing milk in bottles two types of heaters are 

 used. The first is a tank of galvanized iron or cement, with steam pipes 

 suitably arranged on the bottom and sides for heating the water in the 

 tank to the required temperature. The carefully sealed bottles are 

 stacked in the tank and covered with water which is raised to the pasteur- 

 izing temperature and held there for the proper period. Such apparatus 

 is inexpensive and makes pasteurization a possibility for small dairies. 



More costly machines for pasteurizing milk in the bottle are put out 

 by the manufacturers of beer-pasteurizing machinery. In these machines 

 cases of bottled milk by various devices are subjected to showers of water 

 that gradually rise in temperature till they reach the pasteurizing point, 

 where they remain stationary for J^ to % hr., after which the temperature 

 of the showers is reduced till the milk is cooled sufficiently for it to be put 

 in cold storage. 



The great advantage of pasteurizing in the final package is that the 

 cap, bottle and milk are all subjected to the pasteurizing temperature 

 and are not thereafter exposed to contamination. Besides this, the loss 

 from evaporation that occurs in some of the other processes of pasteur- 

 ization is eliminated. The chief disadvantage is the cost. The pasteur- 

 ization has hitherto been done in small units which is an expensive way 

 of handling the milk. The caps used are of types controlled by the 

 several manufacturers thereof so that they are costly and one of these 

 patent caps chips the bottles thereby increasing bottle costs which are 

 also increased by breakage resulting from the strains developed by rapid 

 heating and cooling. Most of the processes that are in use are not re- 

 generative, consequently they are unnecessarily expensive for it is possible 

 to so design the apparatus that the water which is warmed in cooling the 

 hot milk can be utilized in heating up the cold. A good grade of milk 

 can be safely pasteurized in the bottle, but mixed milk collected from divers 

 medium-class producers is likely to be in part made up of the strongly 

 flavored milk of cows approaching the end of the lactation period and of 

 milk that has an unpleasant odor derived from forage, bacterial growths 

 and other sources and such milk is apt to give trouble because the heating 

 may intensify the odors to the detriment of the milk since they have no 

 chance to escape. 



The process, advocated by Ayres and Johnson, of bottling hot milk, is 

 in effect a special development of the holder process. Milk heated to 

 about 145F. is filled into hot steamed bottles and is capped and then 

 cooled by an air blast. The advantages claimed for the process are: ah 

 excellent bacterial reduction; no liability to bottle infection; elimination 



