192 MILK AND DAIRY PRODUCTS PART 



dried calves' stomachs with water, some preservative generally 

 being also added. 



Soxhlet x gives the following directions for the preparation of 

 rennet. The fresh stomachs must first be carefully emptied 

 blown out, dried in the air, and then kept for at least three 

 months. After that part of the stomach which contains no 

 folds has been removed, the rest is cut into pieces about one 

 square centimetre in size. To each 100 of g. stomach, 1 litre 

 water, 50 g. of common salt, and 40 g. of boracic acid are then 

 added, and the whole left to stand for five days at room 

 temperature. Then 50 g. more salt are added for each litre of 

 water, and the fluid filtered off. From 1 litre of water there is 

 obtained about 800 c.c. of filtrate, and this is made up to a litre 

 by the addition of 200 c.c. of 10 per cent, salt solution to which 

 boracic acid has been added to saturation. Such a solution of 

 rennet acts in the proportion of 1 : 10,000, and keeps good for a 

 long time. Nowadays it is seldom that the cheesemaker prepares 

 his own rennet, for there are so many good preparations to be 

 bought at a moderate price. These rennet preparations are 

 sold both in liquid and powder form, or in tablets. The manu- 

 facture of the last two preparations is a trade secret, but they 

 are composed largely of common salt, often as much as 95 per 

 cent. 



A commercial rennet solution ought to be quite clear 

 and without any unpleasant smell, and if kept for a year should 

 not lose more than 25 per cent of its original solution. After 

 being kept in the dark for several months it ought to still act to the 

 extent of 1 : 6000. Good rennet powder ought to be almost 

 colourless and odourless, and nearly completely soluble in 

 water. Rennet powder is naturally much more active than 

 liquid rennet, some of the powders which are sold having 

 a strength of 1 : 300,000 or even stronger. 



To measure the strength of a given rennet preparation 

 it is usual to follow Soxhlet's proposal and estimate, how 

 many c.c. of milk are coagulated in 40 minutes at a tempera- 

 ture of 35 C. by 1 c.c. of liquid rennet or 1 g. of rennet 

 powder. Fleischmann 2 has worked out the following details 



1 Milch- Zeitung, 1877, p. 497. 



2 Fleischmann, Lehrbuch der Mitchwirtschaft. Fourth edition. Leipsic, 

 1907. 



