334 CREAM AND CREAM RIPENING 



The bacterial content of fresh cream obtained by 

 means of the separator is usually low, especially if the 

 milk has been recently drawn from the cow under clean 

 conditions. It is generally lower than that of the milk 

 from which it is derived, since many of the bacteria in the 

 milk are driven to the sides of the separator bowl, and 

 are collected in the protein " slime " along with any 

 other solid particles which may happen to be present. 



Cream of this kind is sweet, bacteria having had no 

 time to develop or bring about any change in it. In 

 fresh cream raised in deep or shallow pans in twelve to 

 eighteen hours by gravitation, bacteria are found in 

 considerable numbers. The organisms occurring in the 

 milk when it is " set " soon multiply, and by the time 

 the cream is a day old the numbers present vary from 

 about 250,000 to over 6,000,000 per cubic centimetre. 



Although sweet, freshly-separated cream is sometimes 

 churned and made into butter, the greatest amount of 

 butter is made from cream which has been kept from 

 thirty-six to forty-eight hours and allowed to become 

 sour either spontaneously or after the addition of special 

 cultures of bacteria. This " souring " process is in reality 

 a complex kind of fermentation termed " ripening" 



In the ripening of cream certain chemical and physical 

 changes occur, and there is a very extensive multiplica- 

 tion of bacteria. 



Cream properly ripened and ready for churning pos- 

 sesses a clean acid taste due to the lactic acid fermen- 

 tation ; the amount of acid allowed to develop before 

 churning should not exceed .5 or .65 percent, calculated 

 as lactic acid. 



In addition to the acid taste, ripening results in tne 

 production of a characteristic taste or flavour of butter 



