TESTING BY RENNET-EXTRACT AND PEPSIN 173 



clogs the tube and, therefore, special pains must be 

 taken to keep it open. For ordinary work the Mar- 

 schall test is convenient but it is not capable of as 

 great delicacy as is the Monrad test. 



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. 



