TESTING MILK BY RENNET-EXTRACT AND PEPSIN 12 j 



METHOD OF TESTING RENNET-EXTRACTS 



Rennet-extract is prepared by soaking calves' stom- 

 achs in dilute brine. This treatment dissolves from 

 the mucous membrane the enzym or chemical ferment 

 that has the property of coagulating milk-casein, a 

 property upon which the process of cheese-making is 

 dependent. The ferment contained in rennet-extracts 

 appears to be the same as pepsin in regard to its ac- 

 tion upon milk casein. Different brands of rennet-ex- 

 tract vary somewhat in their strength, that is, the 

 rapidity and completeness with which they coagulate 

 milk when used in the same amount. It is therefore 

 important to have a means of testing their strength, 

 in order that their value may be definitely known and 

 that cheese-makers may be able to know in advance 

 of using how much they must use for the best results. 

 The Monrad and Marschall tests are available for 

 this purpose. 



In order to test the comparative strength of differ- 

 ent rennet-extracts, one treats different portions of 

 the same milk with the different extracts to be tested. 

 In all other respects, the details of the methods pre- 

 viously given are followed. All conditions must be 

 kept alike in the different tests. The strength of the 

 rennet-extracts is shown by the rapidity with which 

 the milk is coagulated; the stronger the rennet, the 

 less the time of coagulation. 



METHOD OF TESTING PEPSIN 



Pepsin is beginning to be used in cheese-making as 

 a substitute for rennet-extract. Vivian has worked 

 out the important details. The scale-pepsin, of strength 



