THE RELATION OF MICROORGANISMS TO MILK 



399 



Alcoholic Fermentation. — The bacteria as a group are not 

 able to act on the milk sugar and produce alcohol, but it sometimes 

 happens that yeasts get into the milk in sufficient numbers to ferment 

 the milk sugar, producing appreciable amounts of alcohol. To the 

 milk handler this trouble is not usually serious but the action of the 

 yeasts is frequently of considerable importance in the cheese industry. 



Other Fermentations. — It frequently happens that a consider- 

 able variety of disagreeable flavors and odors develop in milk. These 

 may be due to the direct absorption of odors from the foul stable 

 atmosphere or strong-smelUng feeds, such as silage; or they may be,' 

 and no doubt frequently are, the result of the growth of certain types 

 of bacteria which have entered the milk from dirty surroundings. 

 The growth of some of these organisms is frequently the cause of the 

 so-called cowy and stable odors and flavors. 



Commercial Signieicance of Microorganisms in Milk 



Relation of Dirt Contamination to Germ Content. — ^To the 

 commercial milkman bacteria are of importance only as they influence 

 the length of time the milk will keep in a salable condition. The 

 consumers do not want milk that is sour or has unpleasant flavors 

 and odors. In order to sell his milk, therefore, the milkman must 

 avoid the presence of these undesirable conditions, and in proportion 

 as he recognizes the relation between germ life and the quality of 

 his product, will he pay attention to the presence and development 

 of microorganisms in his milk. In like manner, the presence or ab- 

 sence of dirt contamination is important from the commercial stand- 

 point since it bears a relation to the bacterial count, and, therefore, 

 affects the keeping properties of the milk. Under normal conditions 

 there is a fairly direct relation between the amount of visible or soluble 

 dirt and the number of bacteria found in any given lot of fresh milk. 

 This relation may be shown by the following samples taken from four 

 different milk producers: ' 



