PASTEURIZATION 



Pasteurization applied to dairy work is the process of heating milk 

 or cream to a temperature sufficiently high and for a time sufficiently' 

 long to kill most of the organisms in them. The materials should 

 then be cooled to a temperature of 50 F. or lower to prevent germ 

 growth. Cooling the product is just as important a part of the 

 process as is heating, for if there are any organisms not killed by the 

 heating process, they will multiply rapidly if the milk or cream is kept 

 at temperatures favorable for germ growth. Milk or cream from 

 the market standpoint should be kept at just as low a temperature as 

 possible and still not freeze them. 



Pasteurization has for its purpose two objects, (i) the killing of 

 pathogenic organisms, and (2) checking germ growth. The first is 

 the most important, and it is supposed that the process of pasteuriza- 

 tion is efficient in destroying all pathogenic organisms. This supposi- 

 tion is based upon a great many experiments on the thermal death 

 point of such pathogenic organisms as those which cause tuberculosis, 

 typhoid, and diphtheria. 



Pasteurization differs from sterilization in that the latter process 

 kills all living material in and about an object. It is not possible to 

 sterilize milk for market purposes because the high temperatures and 

 length of time required for sterilization change the normal taste of 

 milk and render it objectionable to the consumer. Too high tempera- 

 tures also change the chemical composition of milk, the chief of these 

 changes being the precipitation of albumin and causing the lime salts 

 to become more insoluble. For these reasons both the degree of heat 

 and the length of time employed in the process of pasteurization are 

 limited. 



There are two methods of pasteurization one called the flash 

 method and the other the holder method. In the flash method, milk 

 is heated to a comparatively high temperature for a short time, 

 usually 1 60 F. for one minute or less, and frequently the time which 

 the milk is subjected to the proper temperature is only a few seconds. 



In the holder method, milk is heated to a low temperature for a 

 comparatively long period of time, 140 F. 145 F. for 30 minutes 

 being a very common time and temperature employed. The holder 

 process of pasteurization is considered more efficient than the flash 



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