PURE CULTURE STARTERS 341 



view, and although no single species has been discovered 

 to possess all the qualities for the production of the 

 highest grade of butter, several varieties have been found 

 which are highly beneficial in the preparation of well 

 ripened cream. Single pure cultures of these, or mix- 

 tures of pure cultures of two or more kinds, have been 

 placed on the market, and large quantities of such com- 

 mercial starters are extensively used wherever dairying 

 is practised. 



Jensen suggests that for reliable and satisfactory results 

 a culture should possess the following properties : 



a. It should render cream sour in a short time ; 



b. The organisms in it should be able to grow at 



a temperature of 60 to 65 F. ; 



c. It should coagulate or "thicken" the cream uniformly, 



giving it a clean, acid taste ; and 



d. The butter prepared from the ripened cream should 

 ; possess an agreeable flavour and odour. 



Pure culture starters are sent out either in a dry con- 

 dition mixed with some inert powder, or in a liquid 

 medium such as milk or bouillon. 



They should be kept in a cool place and out of 

 contact with contaminating dust, and when once opened 

 the whole contents should be used immediately. 



Since a tube does not contain enough bacteria to act 

 as a starter for any considerable volume of cream, it is 

 necessary for practical dairy purposes to build up a 

 large bulk of milk containing enormous numbers of the 

 organism. This is done by adding the pure culture to 

 a gallon or two of pasteurized separated milk, and keeping 

 it for about twenty-four hours at 65 to 75 F. until the 

 whole is sour. 



If more is needed, or where a continuous supply is 



