New York Agricultural Experiment Station. 69 



THIS acid combines WITH THE CASEIN IN A DEFINITE WAY. 



In the experiment by Chodat & Hofifman-Bang already referred 

 to, which was a modification of an earUer experiment by von 

 Freudenreich,^ it was shown that, in the presence of chalk to com- 

 bine with the acid, these germs were able to break down all the 

 sugar. That a similar fixation of acid takes place during the , 

 manufacture and ripening of cheese is rendered probable by the 

 rapidity with which the sugar is broken down during the process. 



Sugar determinations made by Hart showed that in one in- 

 stance shortly after the curd was cut the whey contained 4.75 per 

 ct. of sugar while the whey obtained at the time the curd was 

 ready for the press contained but 1.83 per ct. The destruction 

 of the sugar which is left in the curd continues steadily and the 

 sugar disappears from the cheese after a few days at ordinary 

 curing temperatures. In spite of this destruction of sugar with 

 its accompanying formation of acid the presence of free lactic 

 acid in cheese has never been satisfactorily demonstrated. 



In connection with this work upon cheese ripening Van Slyke 

 and Hart have studied two compounds of acid with casein (or 

 paracasein) and have described their chemical properties in 

 Bulletin No. 214 of this Station. 



' The more important of these two compounds from the stand- 

 point of our present knowledge of cheese ripening is an un- 

 saturated combination of paracasein and acid called paracasein 

 monolactate. This compound can be formed from paracasein in 

 large quantities in the presence of dilute acid and is a compound 

 constantly present during the process of cheese-making and ripen- 

 ing. This compound is insoluble in water but is soluble in dilute 

 solutions of common salt (NaCl). Prepared in a fairly pure com- 

 dition this compound draws out in fine threads when applied to a 

 hot iron. It seems that this well known "hot iron" test of the 

 progress of acid formation has thus received a satisfactory 

 explanation. 



5 von Freudenreich, C^n/. /. Bakt., II Abt. 3:2^1. (1897.) 



