210 SCIENCE AND PRACTICE OF DAIRYING. 



are treated with 1 litre of water and 50 grams of salt. After five days 

 50 grams of salt are dissolved in the liquid, and from 100 to 110 c.c. of 

 90-per-cent alcohol are added. The liquid is then filtered. The filtrate 

 thus obtained contains per litre 100 grams of the calves' stomach, 10 per 

 cent of salt, and 8 to 9 per cent by volume of alcohol. Fresh rennet solu- 

 tions prepared in this way lose about 30 per cent of their strength during 

 the first two months, but from that time remain for the next eight months 

 and longer almost quite constant in their strength. On this account, 

 rennet solutions should only be introduced to the markets, and sold, after 

 they are two months old. 



According to Dr. Schmoger, samples of rennet powder of the following 

 brands gave the following results : 



Blumenthal's Blumenthal's 



Rennet Powder. Extract. 



Water, 0'87 85-49 



Nitrogenous organic matter, ... 1-06 0'19 



Non-nitrogenous organic matter, 2 -06 0'84 



Ash, 96-01 13-48 



100-00 100-00 100-00 



The ash of each of these three kinds of rennet consisted essentially of salt, 

 and exhibited only a weak boracic-acid reaction. 



109. The Application of Rennet in Practice. The rennet serves 

 to coagulate milk in a very short period of time, and to obtain from 

 it the coagulum which forms the raw material in the preparation of 

 cheese. A too quick coagulation of milk does not favour the further 

 treatment of the coagulum for conversion into cheese. The period 

 of coagulation in the preparation of most kinds of cheese varies 

 from 15 and 90 to 120 minutes. In the preparation of the majority 

 of cheeses, however, it does not last for more than 40 minutes. 

 Observations show that the coagulum is not immediately formed 

 after the addition of rennet, the physical condition of the milk being 

 changed quite slowly. It first of all gradually becomes viscous or 

 syrupy, then gelatinous, and finally so firm that when the finger 

 is dipped into it and then slowly drawn out again, the coagulated 

 matter gradually breaks. The action of the rennet, however, does 

 not cease with the lapse of the coagulation period. The coagulum 

 becomes firmer, and poorer in water, until, in a longer or shorter 

 period, it reaches as great a degree of firmness as it can possibly 

 attain under existing circumstances. During the subsequent 

 thickening, a green yellow-coloured whey is formed, which increases 



