THE RELATION OF MICROORGANISMS TO BUTTER. 343 



most undesirable flavor, a merchantable product, various means are 

 employed to remove the flavoring substances and to replace them with 

 desirable flavors from the pure cultures. The acidity may be reduced by 

 the addition of lime so that the cream can be pasteurized; the cream may 

 be aerated by passing air through it, or it may be mixed with water and 

 reseparated. After such treatment it is mixed with a large proportion 

 of milk fermented by a pure culture and churned. The resulting pro- 

 duct is constantly sold as the highest grade of creamery butter. 



ABNORMAL FLAVORS OF BUTTER. The abnormal flavors of butter 

 are traceable to the partial replacement of the desirable acid-forming 

 bacteria with other types of microorganisms. Many samples of butter 

 having abnormal flavors have been examined, and the organisms believed 

 to be the cause isolated and studied but it cannot be said that any 

 particular group of microorganisms can be associated with any of the 

 abnormal flavors met. It is asserted that "oily" butter, i. e., that having 

 the taste of machine oil, is caused by bacteria and by microorganisms 

 that decompose the fat, as Oidium lactis, yeasts, and liquefying bacteria. 

 Organisms of the B. coli group that produce a turnip-like flavor in butter 

 have been described by Weigmann. The flavors of putrid butter, fishy 

 butter and also many other abnormal flavors have been ascribed to bacteria. 



The abnormal flavors may be due to the presence in the milk of certain 

 aromatic principles contained in the feed and excreted in the milk. 

 Cabbage, turnips, and others of the cruciferae impart their characteristic 

 taste to the milk and butter. 



DECOMPOSITION PROCESSES IN BUTTER. 



Butter is a finished product at the time it is removed from the modern 

 churn and all subsequent changes are likely to cause more or less dete- 

 rioration. The specific causes of these changes are not well known but 

 it is very evident from a study of the conditions that favor or retard the 

 appearance of the flavors, characterizing these changes, that biological 

 factors are concerned. Sweet-cream butter has very poor keeping 

 qualities. As the proportion of acid-forming bacteria in butter is increased, 

 either by the fermentation of the cream, by the addition of pure cultures, 

 and through the use of the latter in connection with pasteurization, the 

 keeping qualities are enhanced. Of the butter made from ripened cream, 

 that prepared from cream, handled in a clean manner, and thoroughly 



