RENNET AND ITS PROPERTIES. 205 



must be assumed that we are dealing with milk which has not been 

 diluted with water. By the addition of water to milk its acidity is 

 diminished, owing to the fact that the calcium phosphate, with alkaline 

 reaction, is carried into solution. 



The strength of the action of the rennet increases with increasing 

 temperatures, at first slowly, then always more quickly, and reaches its 

 maximum at 41 C., and rapidly decreases from that point with increase 

 of temperature. It has further been established that the rennet coagulum 

 at 15 C. is flocculent and spongy, at 25 to 45 C. it is more or less firm, 

 resembling porcelain, and at 50 C. it is again loose and spongy and jelly- 

 like. Solutions of rennet become permanently inactive if heated to a 

 temperature of over 60 C. If they be kept for some time at a compara- 

 tively high temperature, but below 60 C., they lose their strength. A 

 solution of rennet which acted upon milk (fresh) in the proportion of 1 to 

 3750, and which, to effect sterilization, was heated for 32 hours at 59 to 

 60 C., and which during that time was maintained at a neutral reaction, 

 lost in the above treatment 44 per cent of its original strength. According 

 to experiments carried out in my laboratory by Dr. F. Baumann, solutions 

 of rennet of neutral reaction cannot be sterilized at temperatures over 

 60 C., without at the same time becoming inactive. With regard to 

 the relations of temperature to rennet action between 20 and 50 C., the 

 following numbers may be quoted. The table gives the quantities of 

 milk coagulated at different temperatures between 20 and 50 C. by equal 

 amounts of rennet, taken from the same preparation of rennet ferment, 

 in equal periods of time. Taking the quantity of milk coagulated at 41 C. 

 as 100, the following are the results: 



20 ... 18 36 ... 89 44 ... 93 



25 ... 44 37 ... 92 45 ... 89 



30 ... 71 38 ... 94 46 ... 84 



31 ... 74 39 ... 96 47 ... 78 



32 ... 77 40 ... 98 48 ... 70- 



33 ... 80 41 ... 100 49 ... 60 



34 ... 83 42 ... 98 50 ... 50 



35 ... 86 43 ... 96 



The limits of temperatures between which, in actual practice in cheese- 

 making, milk is coagulated with rennet, are 20 and 48 C. As a rule, the 

 most commonly applied temperature is between 30 and 35 C 



Watered milk coagulates more slowly than pure milk, and by the 

 addition of a large quantity of water, milk can be deprived of the power 

 to form a firm coagulum on the addition of rennet. If solutions of rennet 

 be submitted for some time to the action of light, they gradually decrease 



