300 SCIENCE AND PRACTICE OF CHEESE-MAKING 



dissolving enzym, pepsin. The best evidence at hand 

 at present rather favors the existence of two enzyms. 

 For our purpose, it is immaterial whether there is one 

 enzym or more. Our chief interest in rennet, in con- 

 nection with the cheese-making process, lies in its 

 characteristic property of coagulating milk-casein. 

 Whether the dissolving action of rennet-enzym plays 

 any part in the operation of cheese-making, we do 

 not know at present. We do know, however, that it 

 has some action in the cheese-ripening process (p. 

 362). 



Source of rennet-enzym. — The rennet-extract 

 used in cheese-makmg is a dilute and impure form ot 

 rennet-enzym. ' The usual source of rennet-extract is 

 the fourth stomach of a suckling calf. It is also pre- 

 pared in more concentrated condition in the form of 

 powders and of tablets. Enzyms having the same 

 action as that of rennet are found also in plants and 

 in other animals than calves. Some bacteria pro- 

 duce a coagulating enzym like that in rennet. 



Home-made rennet-extract. — Formerly, cheese- 

 makers purchased rennets from farmers and prepared 

 the extract from time to time as needed. The stomach 

 of a freshly slaughtered calf was cleaned, salted and 

 dried by farmers and sold to the cheese-maker. In 

 preparing the home-made extract, a number of ren- 

 nets are cut in pieces and just covered with salt brine 

 in a suitable vessel, about 3 or 4 pounds of salt 

 being added to 100 pounds of water. The mix- 

 ture is vigorously stirred and pounded. Once a week 

 the rennets are removed from the brine and passed 

 through a press or clothes-wringer and then placed 

 in the brine again. It requires about four weeks to 



