204 Milk and Its Products 



that whatever amount is desired should be uniform 

 from day to day. By far the larger proportion of 

 consumers prefer the flavors that are characteristic of 

 ripening till sufficient acid to slightly coagulate the 

 casein is present. Consumers of delicate taste 

 readily distinguish between the flavors due to a 

 greater or less amount of acid, and it is highly de- 

 sirable that some means of determining the amount 

 of acid present be available. The butter -maker of 

 trained senses has little difficulty in distinguishing by 

 the somewhat thickened and glistening appearance of 

 his cream, when stirred, the proper condition of the 

 cream for churning. Besides this, there are, fortunately, 

 more exact means for determining the acidity. 



Acid tests. Dr. A. G. Manns first suggested the 

 use of an alkali of known strength to determine the 

 proper acidity of cream for churning, and devised 

 what is known as Manns' acid test. It simply con- 

 sisted in neutralizing the acid in the cream with a 

 standard alkali, the standard used being that known 

 to chemists as decinormal, or --, and the acidity was 

 reckoned in terms of cubic centimeters of alkali re- 

 quired to neutralize the acid in a given quantity of 

 cream. In the use of this test, an indicator which 

 changes color according as the medium is acid or 

 alkaline, is used. A convenient indicator is phenol- 

 phthalein, which is colorless in acid solutions and 

 pinkish in alkaline. Later, Professor Farrington* 

 devised tablets containing a known amount of alkali 



*Bull. 32, m. Agr. Exp. Sta. Bull. 52, Wis. Agr. Exp. Sta. 



