PASTEURIZATION OF MILK 215 



will therefore greatly reduce the amount of milk used as 

 a food. It might indeed be possible to learn to enjoy the 

 taste of boiled milk. Children brought up on it like it, 

 while they cannot endure the taste of raw milk. A more 

 serious objection to sterilization is that the heating so 

 changes the nature of the milk that it is less easily digested 

 and assimilated. Boiled or sterilized milk can be digested 

 and assimilated readily enough by persons with strong diges- 

 tive powers, and many children are satisfactorily brought up 

 on it ; nevertheless it is somewhat more difficult to digest 

 and assimilate than raw milk, and frequently children with 

 weak digestive powers do not flourish when fed upon such 

 milk. This fact has prevented the widely extended use of 

 sterilized milk. 



{b) Pasteurization. The objections to boiling milk have 

 led to a different method of using heat for milk preser- 

 vation. Pasteurization has come into wide use in the last 

 few years. It consists of heating milk to a temperature of 

 145° to 170° and maintaining this temperature for from ten 

 minutes to half an hour, according to the temperature used. 

 In this country it is most common to use the lower temper- 

 ature of 145° for half an hour. After heating, the milk must 

 be cooled rapidly. 



It may seem strange that the use of a lower temperature 

 should be more satisfactory than boiling, but the reasons 

 are simple. The chief results to be accomplished are to 

 make it possible to keep the milk longer and to kill all 

 disease germs, and at the same time not to affect the chem- 

 ical nature of the milk. A temperature of 145° for half an 

 hour destroys all the disease germs liable to be in milk, 

 kills most of the lactic-acid bacteria so that the milk will 



