

RELATION OF BACTERIA TO BUTTER 101 



Relation of bacteria to keeping quality of butter. In 

 butter from ripened cream the bacterial content is made up 

 almost entirely of lactic-acid bacteria. During the ripening 

 of the cream the other types of bacteria are overgrown by 

 the lactic-acid type, or are even destroyed by the acid pro- 

 duced. In pasteurized-cream butter the percentage of lactic 

 bacteria reaches its maximum, and the pasteurized product 

 has the best keeping qualities. In butter from sweet cream 

 the bacterial content consists of many forms, the lactic bac- 

 teria being few in number, and the keeping quality of the 

 butter is impaired. 



Exercise. The samples of butter prepared in the exercise on 

 page 95 should be stored in closed vessels in an ordinary refriger- 

 ator and examined at intervals of ten days, in order to determine 

 the rate of deterioration of the sweet-cream butter in comparison 

 with that of butter from the ripened cream. 



Relation of bacteria in wash water to butter. During 

 the washing of the butter the buttermilk is largely replaced 

 by water with its own peculiar bacterial flora. The germ con- 

 tent of wash waters, qualitatively and quantitatively, varies 

 greatly, depending upon the source, manner of storage, etc. 

 Water from a deep well protected from all surface drainage, or 

 from a protected spring, contains the minimum of bacteria, 

 and will exert bub little influence on the quality of the butter. 



Water from streams, shallow wells, or any source unpro- 

 tected from surface water contains many bacteria and usually 

 of kinds injurious to the butter. On storage in tanks and 

 reservoirs the bacterial content of deep-well and spring waters 

 rapidly increases. This is especially true -when the storage 

 tank is not kept perfectly clean. Water freshly pumped is 

 more desirable for use in the dairy than after storage for 

 any length of time. 



