96 MILK 



5. Dilution of Milk and the Relative Quantity of Rennet Used. — 

 Diluting milk retards rennet action by reducing the concentra- 

 tion of casein, calcium salts, rennet, and acidity. Coagulation 

 is not complete, but this can be corrected by addition of soluble 

 calcium salts or acids. The coagulum produced in diluted milk 

 is flaky and not as compact as the one produced in undiluted milk. 



The effect of diluting milk upon rennet action is shown in the 

 following table (Van Slyke and Publow) : 



EFFECT OF DILUTING MILK ON RENNET ACTION 



6. The Age and Quality of the Milk. — Freshly drawn milk 

 coagulates more rapidly than cooled milk because of temperature 

 reduction and the escape of CO2. Milk from different cows, dif- 

 ferent breeds, and different milkings varies in the time required 

 for coagulation. No reason has been found to account for these 

 phenomena except that, as Olsen states, the greater the solids, the 

 longer is the time required for coagulation. A number of tests by 

 Van Slyke give the extremes in the experiments from 40 seconds to 

 50 minutes, and in the same cow a variation of from 45 seconds to 

 60 minutes. At the beginning of lactation milk coagulates more 

 readily than at later periods. Strippings, gargety milk, salty 

 milk, and milk from sick and aged cows coagulates slowly with 

 rennet. 



Rennin is bound by casein in the process of coagulation. This 

 is shown by the fact that after coagulation the whey contains 

 much less rennin than was added. 



Rennin is not injured at 180° C. Dry rennin resists a tem- 

 perature of 100° to 140° C, but liquid rennet is injured by pro- 

 longed heating at 50° to 60° C, and in a short time at higher tem- 

 perature. Rennin is destroyed by alcohol. 



Injection of rennin into animals produces antirennin; in fact, 

 some animals, the horse, for example, have antirennin normally in 

 their blood. 



Raudnitz gives the following summary of the influences of 

 various conditions on rennet action: 



1. The chemical part of the process is accelerated by the dis- 

 tribution of the rennet extract and the quantitative relation to 

 the casein. Perhaps the temperature also has an influence. 

 Salts of alkaline earths and acids probably act by activation of the 

 enzym. 



