THE RELATION OF MICROORGANISMS TO MILK 



465 



to be the result of a very viscid capsule surrounding these organisms 

 (Fig. 144). Representatives of this group are quite resistant to heat 

 and frequently pass uninjured through the methods of cleansing and 

 scalding used under ordinary dairy conditions. Because of this, 

 dairy utensils once infected may become a constant source of infection. 



FIG. 144. Bacillus lactis viscosus from a milk culture. (After Ward.) 



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 

 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 bitterness increases in in- 

 tensity 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. 



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