COAGULATING MATERIALS 31 



which is already secreted to some extent. With the 

 inclusion of other feed, the secretion of pepsin comes to 

 predominate. Rennin has never been separated entirely 

 from pepsin. Both of these enzymes are secreted by 

 digestive glands in the same area, perhaps even by the 

 same glands. They are so closely related that many 

 workers have regarded them as identical. In practical 

 work the effectiveness of rennet preparations has been 

 greatest when stomachs which have digested feed other 

 than milk are excluded. The differences, therefore, 

 however difficult to define, appear to be important in 

 the commercial preparation of rennet. 



It was the practice until a few years ago for 

 each cheese-maker to prepare his own rennet extract. 

 Each patron was supposed to supply so many rennets. 

 Now commercial rennet extract and pepsin are on the 

 market ; however, some Swiss cheese-makers prefer to 

 make their own rennet extract. For sheep's and goat's 

 milk cheese, some makers hold that rennet made from kid 

 or lamb stomachs is best for handling the milk of the 

 respective species. The objection to the cheese-maker 

 preparing his own rennet extract is that it varies in 

 strength from batch to batch and is liable to spoil 

 quickly. Taints and bad odors and flavors develop 

 in it and so taint the cheese. 



46. Preparation of rennet extract. This extract may 

 be manufactured commercially from digestive stomachs 

 of calves, pigs or sheep. An animal is given a full meal 

 just before slaughtering ; this stimulates a large flow of 

 the digestive juices, containing the desired enzymes. 



The stomach is taken from the animal, cleaned, com- 

 monly inflated and dried. It may be held in the dry con- 

 dition until needed for use. Such stomachs are usually 



