BACTERIA AND BUTTER-MAKING 2O3 



cream, and as a practical procedure it has become common to 

 determine the degree of ripening from its amount of acidity. 

 The general practice of butter-makers is to ripen the cream 

 until the acidity reaches about .5 to .65 per cent, of lactic acid. 

 This is determined by the well-known methods given in other 

 places and need not be repeated here (Fig. 60). If the cream 

 is very rich, containing a higher per cent, of fat than usual, 

 the ripening should not be continued to quite such a high per 

 cent, of acidity. The reason for this is that the acidity is de- 

 pendent upon the fermentation of milk sugar, and if the per 

 cent, of fat is very high, there is a smaller amount of milk 

 sugar than usual, and the acidity will not rise so fast ; hence, 

 the ripening becomes completed with a lower acidity than usual. 

 In using the acid test as a method of determining the ripening 

 of cream it must be remembered that this test only gives the 

 grade of acidity, and while this is a gauge it is not the whole 

 ripening. 



3. Use of Starters. The greatest change that has taken 

 place in butter-making in recent years is the adoption of more 

 and more careful methods of regulating cream ripening by the 

 use of starters. Twenty years ago they were only occasionally 

 used; to-day their use is well-nigh universal. A starter simply 

 consists of a lot of cream or milk, which has become already 

 soured, and is added to the mass of cream in the cream vat 

 for the purpose of controlling the ripening process. It was 

 first used by butter-makers in cold weather only. In the early 

 days of creameries it was found that during the cold weather 

 the cream frequently would not ripen quickly, and though left 

 for the ordinary time in the cream vat, it was not ready to 

 churn when desired. This was easily obviated if the proper 

 amount of sour cream was added to it. This was called 

 "starting" the ripening, and hence the name starter. Although 

 used originally only to start the process, it has been found that 

 starters have other advantages. By their use butter-making 



