248 Milk and Its Products 



a correspondingly retarding effect. Thus, the develop- 

 ment of lactic acid by rendering the lime salts more 

 soluble hastens the action of rennet on the milk. On 

 the other hand, when milk is heated to a tempera- 

 ture above 150 P. a part of the lime salts is made 

 insoluble, and the action of the rennet correspond- 

 ingly retarded, even though the milk be again cooled 

 to a temperature at which rennet is active. The 

 coagulability of milk is similarly affected by the addi- 

 tion of any lime salt not normally present in milk. 

 Thus, if calcium oxalate or other insoluble salt of 

 lime is added to milk, the action of rennet is 

 retarded. On the other hand, the addition of cal- 

 cium chloride or other soluble salt is followed, by a 

 quicker action of the rennet. 



The rennet skin should be obtained from an 

 animal of some age. Still-born calves, or calves less 

 than three days old, furnish a rennet of very inferior 

 quality. The calf should be slaughtered three or 

 four hours after it has had a full meal, and the 

 fourth stomach carefully taken out. This should be 

 emptied by turning inside out and any particles 

 of foreign matter carefully picked off ; it should 

 not be washed with water. It should then be 

 sprinkled with salt and stretched in such a manner 

 that it will readily dry. 



At the present time the preparation of the rennet 

 extract from the skins is entirely a commercial one, 

 and rennet so much superior, on account of its 

 uniform strength and freedom from taints, is fur- 

 nished in this way that it is not advisable to prepare 



