Preservation of Milk. 123 



water is, in part, due to its freedom from carbon dioxide. 

 The production of this cooked flavor is dependent upon 

 the time and temperature of exposure. It has been 

 claimed that heated milk is less digestible than raw, and 

 a considerable amount of experimental work has been 

 done, both on animals and children, in order to deter- 

 mine the relative digestibility of heated and raw milk. 

 The results obtained have been contradictory. It is 

 claimed that heated milk causes such diseases as rick- 

 ets, scurvy and marasmus in children. It is probably 

 true that milk heated to the boiling point is less fitted as 

 food for the young child than raw milk, but, on the 

 other hand, it has not been proven that properly pas- 

 teurized milk is an unsuitable food for children. The 

 best evidence has been accumulated in recent years, in 

 many of the large cities of this country and of Europe, 

 where pasteurized milk has been used with the greatest 

 success in the feeding of children of all ages. 



The heated milk does not curdle readily when rennet 

 is added due to the precipitation of the lime salts by 

 heat. The curdling power can be restored by the ad- 

 dition of soluble lime salts or of acids. 



Purpose of pasteurization. There are two reasons 

 for the pasteurization of milk : ( 1 ) To improve the keep- 

 ing quality; (2) To destroy any pathogenic bacteria it 

 may contain. The first may be called the economic rea- 

 son ; the second, the hygienic reason fnr pasteurization. 

 In ,the selection of a proper pasteurizing temperature, 

 two factors must be taken into account : First, the effect 

 of heat on milk, and second, the temperature necessary 

 to destroy those forms of bacteria that are of the greatest 

 importance, as far as the keeping properties are con- 

 cerned, and the pathogenic bacteria that might possibly 



