68 Agricultural Bacteriology. 



development of dairying and is still employed by many 

 butter makers. It has, however, been gradually sup- 

 planted by the pure-culture or commercial starter. This 

 more recent advancement is due to the discovery of the 

 Danish bacteriologist, Storch, who was the first to show 

 the relation which bacteria hold to the ripening of cream. 

 Instead- of relying on natural fermentations to produce 

 the starter, he separated, from ripened cream, the specific 

 organisms found therein and tested them as to their 

 flavor-producing properties. Those which were found to 

 produce the most desirable flavors were then cultivated 

 in quantities so that they could be distributed to the 

 creameries. 



The pure culture is thus supposed to be a more highly 

 selected type of the organism than would be found if re- 

 liance was placed on natural fermentations alone. The 

 pure cultures are extensively used at the present time 

 and aid in maintaining uniform conditions in the ripen- 

 ing of the cream since the butter maker can use the same 

 organism continuously. "When the starter propagated 

 in the creamery becomes undesirable for use in the cream, 

 a new pure-culture starter is obtained from 1 the manu- 

 facturer. 



Pasteurization of cream for butter making. The 

 cream to which the pure-culture starter is added con- 

 tains, of course, as does all the milk and cream, lactic 

 acid and other organisms of various kinds. These nat- 

 urally develop in the cream to a greater or less extent 

 when the pure-culture starter is added to raw cream. 

 The flavor of the butter is thus the result of the combined 

 effect of both the acid bacteria already present and those 

 added. It was as though grain had been sown on an un- 

 plowed and weedy field. 



