Bacteria and Butter- Making. 137 



failure to discriminate between these qualities. While all 

 three are produced simultaneously in ordinary ripening, it 

 does not necessarily follow that they are produced by the 

 same cause. If the ripening changes are allowed to go too 

 far, undesirable rather than beneficial decomposition pro- 

 ducts are produced. These greatly impair the value of but- 

 ter, so that it becomes necessary to know just to what extent 

 this process should be carried. 



In cream ripening there is a very marked bacterial 

 growth, the extent of which is determined mainly by the 

 temperature of the cream. Conn and Esten l find that the 

 number of organisms may vary widely in unripened cream, 

 but that the germ content of the ripened product is more 

 uniform. When cream is ready for the churn, it often 

 contains 500,000,000 organisms per cc., and frequently 

 even a higher number. This represents a germ content 

 that has no parallel in any natural material. 



The larger proportion of bacteria in cream as it is found 

 in the creamery belong to the acid-producing class, but in 

 the process of ripening, these forms seem to thrive still 

 better, so that when it is ready for churning the germ con- 

 tent of the cream is practically made up of this type. 



Effect on Churning. In fresh cream the fat globules which 

 are suspended in the milk serum are surrounded by a film of 

 albuminous material which prevents them from coalescing 

 readily. During the ripening changes, this enveloping 

 substance is modified, probably by partial solution, so that 

 the globules cohere when agitated, as in churning. The 

 result is that ripened cream churns more easily, and as it 

 is possible to cause a larger number of the smaller fat- 

 globules to cohere to the butter granules, the yield is 



1 Conn and Esten, Cent. f. Bakt., II Abt., 1901, 7: 746. 



