METHODS OF TESTING THE ACIDITY OF MILK 149 



The number of cubic centimeters of alkali used, mul- 

 tiplied by 2, equals the per cent, of acid in the cheese. 

 Much higher results are obtained if one treats the 

 cheese instead of its water extract with alkali, because 

 the nitrogen compounds of the cheese neutralize alkali. 



RELATION OF FAT IN CREAM TO ACIDITY OF 

 CREAM-RIPENING 



Cream rich in fat ripens, that is, becomes acid, more 

 slowly than cream poor in fat. This is so, because the 

 larger the percentage of fat in cream the smaller is 

 the percentage of sugar, and the sugar is the source of 

 lactic acid. The favorable influence of ripening upon 

 the process of churning is believed to be due to the 

 action of the acid upon the calcium casein of the cream, 

 converting it into calcium lactate and so lessening its 

 tenacious hold upon the fat-globules in emulsion. The 

 fat itself of the cream is not changed. The amount 

 of acid to be formed in cream-ripening is, therefore, to 

 be governed more by the amount of calcium casein in 

 the cream than by any other constituent. The less fat 

 there is in normal cream, the more casein there will be, 

 and the greater the per cent, of acidity needed. The 

 more fat there is in cream, the less calcium casein there 

 will be, and the less the amount of acid needed. These 

 statements conform to practical experience. Thus, 

 it is found that in cream containing 25 per cent, of 

 fat, it is necessary to produce nearly .7 per cent, of 

 acid in order to get the results sought by ripening, 

 while, in cream containing 35 per cent, of fat, less 

 than .6 per cent, of acid is sufficient. 



To ascertain how much acid should be formed in 



