4 BULLETIN 342, U. S. DEPARTMENT OF AGEICULTUEE. 



Table II. — Proportion of total milk supply pasteurized in certain cities. 1 



City. 



Per cent 

 pasteurized. 



City. 



Per cent 

 pasteur- 

 ized. 





80 

 80 

 57 

 88 





85 





Pittsburgh, Pa 



95 





70 



New York, N. Y 











1 In the small cities the per cent of milk pasteurized is much lower. 

 METHODS OF PASTEURIZATION. 



At present there are three processes of pasteurization practiced in 

 this country. The first is known as the flash, or continuous, process ; 

 the second, the holder, or holding, process ; and the third is known as 

 pasteurization in the bottle. 



The flash process consists in heating rapidly to the pasteurizing 

 temperature, then cooling quickly. In this process the milk is heated 

 from 30 seconds to 1 minute only, usually at a temperature of 160° F. 

 or above. 



In the holder process the milk is heated rapidly to temperatures of 

 from 140° to 150° F. and held for approximately 30 minutes, after 

 which it is rapidly cooled. Sometimes the milk, instead of being 

 held at a certain temperature in one tank for 30 minutes, is merely 

 retarded in its passage through several tanks so that the length of 

 time is required for the milk to pass through. In such cases, how- 

 ever, there is no assurance that all the milk is held for the desired 

 time. The holder process, which is gradually replacing the flash 

 process, is more effective and is superior in every way. 



Pasteurization in bottles is the latest development of the process 

 to be used on a practical scale. This process, as first practiced, con- 

 sisted in putting the raw milk into bottles with water-tight seal caps, 

 then immersing them in hot water until heated to 145° F. and hold- 

 ing them at that temperature for 20 or 30 minutes. The cooling 

 was accomplished by gradually lowering the temperature of the 

 water until that of the milk reached 50° F. This method is now in 

 use in several milk plants. The advantage of this process is in the 

 fact that the milk after heating is not exposed until it reaches the 

 consumer, thereby eliminating any danger of reinfection with dis- 

 ease-producing organisms through handling. For this process to 

 be successful it is necessary, of course, that the seals be absolutely 

 water-tight, as the bottles are submerged in water, and, during cool- 

 ing, a defective cap might allow infection by polluted cooling water. 

 The disadvantage of this process is in the increased cost of pasteuriz- 

 ation, caused by the cost of the seal caps. It is claimed, however, 

 that the saving in milk losses by pasteurization in bottles makes up 



