Preservation of Milk. 133 



Efficiency of pasteurizing. It is easy to destroy over 

 99 per cent of the bacteria present by the use of any of 

 the modern types of machines. The number remaining 

 after treatment will be largely dependent, other things 

 being equal, upon the number of bacteria before pasteur- 

 ization. The pasteurizing process is not one by which 

 poor milk can be changed into good milk, nor is it legit- 

 imate to use the process in place of cleanliness, as is 

 sometimes done. There is a legitimate field for the pro- 

 cess in the handling of market milk, as well as in the 

 creamery; but it should be used to improve the keeping 

 quality, and to insure the freedom of the milk from 

 pathogenic bacteria, when other protective measures have 

 been carried as far as possible under the prevailing con- 

 ditions. 



Details of process. If the process is to be successful, 

 clue attention must be given to certain details. In the 

 treatment of market milk, care should be taken to use 

 only that in which the acidity has not materially in- 

 creased. A fair standard is about 0.2 per cent. High 

 acid milk usually means old milk or dirty milk, either 

 of which is very likely to contain many more spore- 

 bearing bacteria than clean, fresh milk. The greater 

 the number of spores, the more rapidly will the pas- 

 teurized milk spoil. If it is possible to exercise any se- 

 lection of milk prior to pasteurization, the rapid test 

 for determination of acidity will prove of great ad- 

 vantage. 



Care should be taken to prevent fluctuations in the 

 temperature to which the milk is heated. With varying 

 steam pressure and variations in the rate of flow of 

 milk, these fluctuations may be very considerable. Reg- 

 ulators are now made that will control the temperature 

 within narrow limits. 



