Farm Dairying 



249 



356. Changes in Milk. Bacteria are the active agents 

 of change in milk. The souring of milk is due to the 

 formation of acid by bac- 

 teria. When the acid 

 accumulates in sufficient 

 quantity, it combines with 

 the protein to form the 

 clabber. If bacteria are 

 kept out of the milk, it will 

 keep sweet indefinitely. 

 The flavors developed in 

 milk and butter are due 

 to the presence of certain 

 kinds of bacteria. Some give the butter undesirable 

 flavor, and some greatly improve the flavor. The flavor 

 of butter, however, may be controlled by destroying 

 all the bacteria in the milk or cream by Pasteurization. 

 (U 367.) After the milk or cream has been freed from 

 the desirable, as well as undesirable germs, by the 

 process mentioned, it is then cooled and desirable ones 



Fig 1161. Microscopic appearance of 

 ordinary milk showing fat globules 

 and bacteria in the milk. The 

 cluster of bacteria on left side are 

 lactic acid -forming germs. After 

 Russell, Wisconsin Bulletin, No. 62. 



Progeny of 

 a Single Germ 

 in twelve hours. 



Fig. 162. Cooling hinders growth of bacteria. After Russel, 

 Wisconsin Bulletin, No. 62. 



