48 CREAMERY BUTTER MAKING 



be due to strippers' milk and to certain classes of feeds 

 and weeds, but most frequently to bacteria. This class 

 of bacteria has not yet been studied very thoroughly but 

 we know a great deal about it in a practical way. In 

 milk and cream in which the action of the lactic acid 

 germs has been suppressed by low temperatures, bitter- 

 ness due to the development of the bitter fermentation is 

 almost certain to be noticeable. When the temperature 

 is such as to cause a rapid development of the lactic 

 fermentation, the bitter fermentation is rarely, if ever, 

 present. It is quite evident from this that the bitter 

 organisms are capable of growing at much lower tem- 

 peratures than the lactic and that so long as the latter 

 are rapidly growing the bitter fermentation is held in 

 check. 



This teaches us that it is not safe to ripen cream below 

 60 F. The author has found that cream quickly ripened 

 and then held at a temperature of 45 for twenty-four 

 hours would show no' tendency toward bitterness, while 

 the same cream held sweet at 45 for twenty- four hours 

 and then ripened would develop a bitter flavor. This 

 indicates that the lactic acid is unfavorable to the develop- 

 ment of the bitter fermentation. 



The bitter germs produce spores capable of resisting 

 the boijing temperature. This accounts for the bitter 

 taste that often develops in boiled milk. 



2. SUMY OR ROPY FERMENTATION. 



This is not a common fermentation and rarely 

 causes trouble where cleanliness is practiced in the dairy. 

 The bacteria that produce it are usually found in impure 

 water, dust, and dung. These germs are antagonistic to 



