CHAPTEE VIII 



Rennet and Its Action 



BEFORE passing on to consider cheese, it will be best 

 to discuss the nature and action of rennet. 



The chief constituent of ordinary cheese is the 

 casein of milk, and the object of the cheese-manu- 

 facturer, therefore, is to separate this casein from the 

 milk. This is effected by coagulating it. From a 

 very remote period it has been customary to effect 

 the coagulation of milk in either of the two following 

 ways, viz. by allowing it to become spontaneously 

 sour, or by treating it with rennet. For long these 

 two processes were regarded as essentially the same 

 in their nature, and although several observers 

 noticed that certain differences existed in the re- 

 action produced, for example, by the respective kinds 

 of coagulation little notice was paid to this fact. 



Occurrence of Rennet Ferment. Before dis- 

 cussing the action of rennet, it will be well to say a 

 few words on the nature of this substance. With re- 



