326 MICROBIOLOGY OF MILK AND MILK PRODUCTS. 



tions. Because of this, dairy utensils once infected become a constant 

 source of infection. This trouble can be effectively stopped by a 

 thorough scalding of all utensils coming in contact with the milk. 



BITTER FERMENTATION. Bitter flavors in milk may be the 

 result of bacterial changes after the milk has been drawn, or due to 

 certain strong feeds which the cows have consumed. If the cows 

 are allowed to eat certain kinds of vegetation, such as "rag weed" 

 and certain other plants, they may impart a bitter taste to the milk, 

 in which case the abnormal flavor will be apparent when the milk 

 is fresh and usually becomes less pronounced as the milk becomes 

 older, because of the volatile nature of the substances causing the 

 bitterness. Most of the cases of bitter milk and cream, however, are 

 due to the growth of certain types of bacteria in which case the bit- 

 terness increases in intensity with the age of the milk. Some of the 

 species capable of producing bitter milk grow at quite low temperatures, 

 which accounts for the fact that the most trouble with bitter flavors is 

 found in milk and cream which has been held at low temperatures for 

 some time. 



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 considerable 

 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 smelling 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 SIGNIFICANCE 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 



