PART IV. 



PASTEURIZATION AND STERILIZATION 



IN the household, milk is boiled to make it keep 

 longer and this process serves also to kill any pathogenic 

 bacteria that may be present. Little by little, the public 

 has learned that milk often contains disease producing 

 germs and that small children are especially exposed to 

 their harmful effects, so the custom has become more or 

 less general of sterilizing milk intended for infants. 

 Quite naturally, the idea developed to sterilize market 

 milk, by heating before it was offered for sale. By 

 this means, the following desired results have been ob- 

 tained: the milk keeps for a longer time, it loses its 

 capacity for infection, and the annoying process of ster- 

 ilization in the home is avoided. In most large cities 

 there are one or more companies engaged in the sale of 

 sterilized or pasteurized milk. 



The difference between pasteurization and steriliza- 

 tion consists, essentially, in the greater degree of heat 

 applied during the latter process. 



I. PASTEURIZATION 



By pasteurizing a fluid is generally understood heat- 

 ing it to a temperature below boiling which is sufficient 

 to increase its keeping qualities. It is sometimes used 

 to indicate heating to 50 to 60 C. (122 to 140 F.) 

 and sometimes the use of a higher temperature. In ref- 

 erence to milk and dairy products, the term " pasteur- 

 ization " is used in a more definite sense. In butter- 



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