RELATION OF BACTERIA TO DAIRY PRODUCTS 569 



later fermentations, but if the cream has been produced under 

 unsanitary conditions and miscellaneous fermentations allowed 

 to develop, he must depend on pasteurization and the use of 

 pure culture starters for the developing of the desired flavor in 

 his finished butter. 



Freshly made butter contains large numbers of bacteria, in 

 spite of the fact that the larger percentage of those contained 

 in the cream have been removed in the buttermilk and in the 

 process of washing and working the butter. 



In order that butter may keep well, it should be held at suffi- 

 ciently low temperatures to prevent the rapid development of 

 the bacteria which it contains. 

 Abnormal flavors. 



Frequently undesirable flavors will appear in butter, seri- 

 ously injuring its commercial value. Most of these "off" 

 flavors are probably due to the action of certain kinds of bac- 

 teria in the cream, a condition known as "metallic" flavor is 

 not uncommon, and according to Guthrie may be caused by 

 direct absorption of metals by the cream or by the action of 

 certain members of the Pact, lactis acidi group of bacteria 

 which are able to grow in the highly acid cream. Rogers states 

 that "fishy" flavor is caused by a slow, spontaneous chemical 

 change to which acid is essential and which is favored by the 

 presence of small amounts of oxygen. 

 Disease bacteria in butter. 



If the milk and cream from which butter is made contains 

 disease-producing bacteria, they may persist through the manu- 

 facturing process and be incorporated in the finished butter. 

 Since so large a percentage of the bacteria in the cream are re- 

 moved in the buttermilk and wash water, the danger of trans- 

 mitting these diseases through butter is much less than in the 

 case of milk. It has been shown 1 that tubercle bacilli may be 



1 Annual Report Bureau of Animal Industry, 1909, Moler, Wash- 

 burn, and Rogers. 



