17 



method and many boards of health have forbidden the use of the flash 

 method of pasteurization of milk sold under their jurisdiction. 



Pasteurization should never be used as a means of placing dirty 

 milk upon the market. While the process does kill the micro- 

 organisms found in milk it does not always destroy their products, 

 and if badly contaminated milk is pasteurized and placed upon the 

 market, although its germ content may be small, it may still be unfit 

 for human consumption. 



EXERCISE IV 

 PASTEURIZATION BY THE HOLDER METHOD 



NOTE: This exercise should be performed in combination with 

 Exercise V. 



1 . Thoroughly mix four cans of milk by pouring from one can to 

 another. Take in a sterile bottle a small amount of milk from each 

 can and place the sample on ice until it can be plated for bacteria. 

 Two of the cans of milk are to be used in Exercise V. 



2 . Thoroughly scald the machine. This may be done by running 

 hot water through the coils. Pasteurize two cans of milk at a tem- 

 perature of 140 F. for 30 minutes. After heating the milk for the 

 proper time at the proper temperature, cool the milk to as low a 

 temperature as possible in the time allowed and lower the temperature 

 of the milk as rapidly as possible. Carefully record the weights of 

 the milk used, the time required to raise the milk to 140 F., the 

 temperature to which the milk was cooled, the temperature of the 

 refrigerating substance as it enters the coils, and the time required for 

 the entire process. 



When the process is complete, take in a sterile bottle a sample 

 of the milk to be plated for bacteria. Compare the bacteria counts 

 obtained with that of the raw milk, and that from the milk pas- 

 teurized by the flash method. 



