RELATION OF BACTERIA TO DAIRY PRODUCTS 557 



or "holding" process, and sometimes the term "held pasteuri- 

 zation" is applied. By the latter method the milk is held for 

 approximately thirty minutes at the temperature desired. 



The "flash" process. The method of pasteurizing by the 

 flash process is as follows : The milk flows from the receiving 

 tank to the pasteurizer, where it is heated at temperatures 

 from 160 to 165 F. for from thirty seconds to one minute. 

 After heating it flows to the cooler, where it is cooled to from 

 35 to 45 F., and is then immediately bottled and placed in 

 refrigerators at temperatures ranging from 35 to 45 until 

 time for distribution. 



The "holder" process. The holder process is the same as 

 the flash process, except in the temperatures used and the 

 length of the heating period. The milk is heated in the same 

 pasteurizer as in the flash process, but at lower temperatures 

 140 to 150 F. After being heated it flows to the holding tank, 

 where it is held for approximately thirty minutes, and is then 

 cooled and bottled as in the flash process. The holder process 

 possesses numerous advantages over the flash process. To 

 insure a complete destruction of disease-producing organisms 

 with the holder process, a temperature of 140 F. for 30 minutes 

 is sufficient. With the flash process a temperature of 160 F. 

 or higher is required to accomplish the same result. A much 

 higher percentage reduction of bacteria can be obtained with 

 the holder process than is possible with the flash process, unless 

 very high temperatures are used, and the bacterial reductions 

 will be more uniform in the holder process, due to the heating 

 of all the milk to the required temperature. When using a 

 flash machine it is often found that the percentage bacterial 

 reduction is greatly lowered, even though the temperature is 

 carefully maintained. Such an occurrence is due to the fact 

 that all of the milk is not heated to the temperature indicated 

 by the thermometer. Again, the use of the high temperatures 

 necessary for efficient results by the flash process is objection- 



