132 Dairy Bacteriology. 



have been introduced as a means of hastening and rendering 

 the ripening process more nniform. In the use of these, 

 bacterial growths are added to assist in the ripening of 

 cream, although generally no knowledge of the bac- 

 terial processes involved has until recently been taken 

 into consideration. These methods are a great improve- 

 ment over the previous let-alone policy of cream-ripening 

 as one is often able to exclude in this way, undesirable 

 fermentative changes. For starters of this sort, several 

 different materials are used, as sour-milk, buttermilk, or 

 whey, all of which are liquids rich in bacteria. 



3. Artificial starters (bacterial cultures}. A much 

 more scientific method of ripening cream has been intro- 

 duced within the last few years and is now being exten- 

 sively used in Scandinavian, Danish, and German dairies. 

 This method dates from the labors of Storch, 1 who in 

 1890 proposed and introduced the use of pure cultures 

 that have been selected on account of their ability to 

 produce a desirable ripening change in cream. 4 His in- 

 vestigations opened up a new field of research which has 

 since been diligently prosecuted in both Europe and 

 America. 



133. Principles of pure culture cream-ripening'. 

 This method rests on the principle that a selected culture 

 that has been chosen on account of its favorable ripen- 

 ing qualities will be able to produce a similar fermenta- 

 tion in cream, if the proper conditions are present. To 

 get the best results, it is evident that the selected culture 

 will have favorable conditions for its development, if the 

 pre-existing bacteria in the cream are first destroyed. In 

 this way competition is reduced to a minimum. This 

 preparation of the cream is accomplished by pasteurizing 



1 Storch, Milch Zeit., 1890, p. 304. 



