x e . CLEAN MILK 



milk germs) are destroyed and so the milk does not sour but putre- 

 fies when it ages. 



Pasteurization prevents milk from being properly curdled by 

 rennet and so unfits milk for cheese-making. Cheese is, however, 

 now being made from pasteurized milk to which is added a 

 " starter." Pasteurized milk or cream may be used to advantage 

 for butter-making when the lactic acid germs are added in the form 

 of sour milk, known as a " starter," which will be described later. 

 Since butter frequently contains tubercle bacilli (tuberculosis 

 germs) it should always be made from cream derived from tuber- 

 culosis-free cows or else cream should be properly pasteurized. If 

 we must have dirty milk, pasteurization is the best remedy for this 

 unhappy state of affairs, but it may well prove undesirable to thus 

 remove the incentive to dairymen to produce clean milk. If done 

 at all for the market, it should be done thoroughly (see pp. 217-19), 

 followed by rapid cooling.* If milk is not cooled down to allow- 

 point after pasteurization, spores will develop which have escaped 

 destruction on account of their great resistance to heat, and these 

 will result in germs which, while not souring milk, act on the casein 

 to cause it to curdle and perhaps become poisonous and putrid. 

 In Europe pasteurization of milk is much more common than in 

 this country, since ice is in less common use. In Denmark it is 

 required by law, so that tuberculosis may not be spread when skim 

 milk and buttermilk are returned from the creameries and fed to 

 calves and pigs. This custom should be imitated in the United 

 States, since the young stock are not only protected from disease, 

 but the keeping quality of the skim milk is so much improved. A 

 higher temperature than 165" P. gives the milk a boiled taste and 

 alters its composition to some extent. Steam or boiling water are 

 used to destroy germs in or on dairy utensils. 



* Pasteurized milk which is sold for general consumption should be 

 always marked as such, in order that infants shall not be harmed by its use.- 

 (See p. 187.) 



