130 Testing Milk and Its Products. 



generally neutralized by 15 to 20 cc. of this tablet solu- 

 tion, representing from .15 to .20 per cent, of acid. A 

 mildly sour cream is colored by 35 ce. tablet solution, and 

 a sour cream ready for churning by about 50 to 60 cc. 

 tablet solution. As the cream ripens, its acidity in- 

 creases. The rate of ripening depends largely on the tem- 

 perature at which the cream is kept. Cream containing 

 .5 to .6 per cent, of acid will make such butter as the 

 general American market demands at the present time. 

 Cream showing an acid test of .55 per cent, may not be 

 too sour, but .65 per cent, of acid is very near, if not 

 on the danger line, since such cream is likely to make 

 strong flavored, almost rancid butter. Each lot of cream 

 should be tested as soon as it is ready for ripening, and 

 the result of the test will show whether the cream should 

 be warmed or cooled in order to have it ready for churn- 

 ing at the time desired. Later tests will show the rate 

 at which the ripening is progressing, and the time when 

 the cream has reached the proper acidity for churning. 

 144. The influence of the richness of cream on the 

 acid test has been studied by Professor Spillman,^ and 

 others.^ Since the acidity develops in the cream serum, 

 it follows that an acidity of, say .5 per cent, in a 40 

 per cent, cream represents a larger acidity than in 20 

 per cent, of cream, e. g. ; in the former case we have .5 

 gram of acid in 60 grams of serum (=.83 per cent, of 

 the serum) ; in the latter case .5 gram acid is found in 

 80 grams serum (^.63 per cent, of the serum) . There- 



• Washington experiment station, bulletin 32. 



' Chicago Dairy ProOiice, April 21, I'JOO, p. SO ; Iowa expt. sta., bull. 

 52. 



