CHAPTER IV 



Fermentation 



THE changes commonly occurring in milk and 

 popularly called souring are caused by minute 

 forms of plant life, called bacteria, most of which 

 gain access to the milk after it leaves the cow, not 

 being found in the udder of the healthy animal, 

 except in the ducts of the teat. These bacteria 

 during the process of their growth change the con- 

 stituents of the milk, forming new products, such 

 as gases, acid, bitter flavors, and sometimes colors, 

 as pink or blue milk, and sometimes producing 

 slimy or ropy milk. Others produce the flavors that 

 are so much desired in good butter and other dairy 

 products. With many varieties always present, the 

 kind that will dominate depends largely on the tem- 

 perature at which milk or cream is kept. All bac- 

 teria are not, therefore, undesirable or harmful. 

 Bacteria are like the higher forms of plants, many 

 beneficial to man, some harmful and undesirable. 

 Knowledge of method of growth and multiplication 

 enables man to control them and make them serve 

 his interests. 



Bacteria. They consist of a single cell, and are 

 so small that a drop of milk may contain millions ; 

 they grow rapidly at a temperature of from 60 to 

 90 ; they require food and moisture like higher 

 forms of plant life, milk furnishing an ideal medium 



