I02 MODERN METHODS OF TESTING MILK 



power of neutralizing alkali to some extent. The per- 

 centage of acid in milk can be used as a guide in 

 ripening the milk before adding rennet, in the rate of 

 heating (cooking) the curd, in the regulation of the 

 piling of the curd, in the time of milling, etc. 



TESTING THE ACIDITY OF CHEESE 



From a sample of cheese, prepared in the manner 

 described on page 8i, weigh nine grams and to this 

 add water at a temperature of ioo° to iio° F. until 

 the volume equals 90 to 100 cc. Agitate vigorously 

 and filter. To the filtrate add alkali solution, each 

 cubic centimeter of which equals .01 per cent, of lac- 

 tic acid, carrying out the test as with milk, cream, etc. 

 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, ahd 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 



