New York Agricultural Experiment Station. 191 



INTRODUCTION. 



In Bulletin No. 203 of this Station, we published the results of 

 some preliminary work, in which we made a study of the relation, 

 of the enzymes contained in milk to the ripening process of 

 cheese. We aimed to exclude bacterial action in cheese and 

 thus limit our study to the results produced by the enzymes 

 present in the milk when made into cheese, including rennet- 

 enzyme. In our previous work, we made no attempt to dis- 

 tinguish between the dififerent enzymes in respect to their indi- 

 vidual action in cheese-ripening. The object of the work 

 described in this bulletin was, primarily, to ascertain to what 

 extent the proteolytic phenomena of cheese-ripening are due to 

 the action of an enzyme contained in the rennet-extract used in 

 cheese-making. 



It has been quite generally believed that the rennet-extracts 

 used in the manufacture of cheese contain not less than two 

 enzymes or ferments, called rennin and pepsin, one ferment 

 coagulating milk-casein and the other converting milk-casein and 

 paracasein, under favorable conditions, into soluble forms of 

 nitrogen compounds. The present tendency, however, is in the 

 direction of the belief that both kinds of action are due to the 

 presence of only one enzyme. The presence of a proteolytic 

 ferment in rennet-extract is readily understood, when we con- 

 sider its source, which is the stomach of a suckling calf. 



For years the weight of opinion was against the belief that 

 rennet has any other function in cheese-making than simply to 

 coagulate milk-casein. In Bulletin No. 54, page 267, the 

 results of some experiments made at this Station in 1892 are 

 given, and it was shown that cheese made with larger amounts of 

 rennet furnished greater quantities of soluble nitrogen com- 

 pounds than did cheese made with smaller amounts of rennet. 

 In 1899 some additional work was done, confirming the results 

 previously obtained. Babcock, Russell and Vivian^ have made 

 a very thorough investigation of this subject, showing that, in 

 the case of normal cheese, increased use of rennet resulted in a 

 more rapid increase of soluble nitrogen compounds, especially 



1 Annual Report. Wis. Exp. Sta., 17 : 102 (1900). 



