208 SCIENCE AND PRACTICE OF DAIRYING. 



suitable methods from the rennet solutions, and are rich in rennet 

 ferments. 



A commercial solution of rennet should possess an inviting 

 appearance, should be clear, and should neither possess a disagree- 

 able nor a strongly aromatic smell. They must possess keeping 

 properties, and should not lose in the course of a year more than 25 

 per cent of their strength. They should not be too weak, and if 

 kept for several months protected from the light, they should possess 

 a strength of 1 to 6000; and, finally, they ought not to be too dear. 

 A litre of a good rennet solution, possessing a strength of from 1 to 

 10,000 to 1 to 6000, should not cost more than two to three marks. 



A good commercial rennet powder should have an appearance 

 almost entirely white, should possess practically no smell, and on 

 being dissolved in water should leave only a very small residue. 

 It should obviously not contain lead, a body which has been found 

 in considerable quantities in some samples. As rennet powder is 

 richer in the amount of ferment it contains, and poorer in foreign 

 constituents than the commercial rennet solutions, it possesses an 

 advantage over the solution. Up till now, however, the use of the 

 powder in practice has been less popular than the use of the more 

 convenient commercial rennet solutions, since there are different 

 and not altogether unimportant inconveniences attached to its use. 

 Rennet powder must be carefully protected, for example, from damp, 

 since if it become moist it decomposes and putrefies. Further, 

 before its use it must be perfectly dissolved for fifteen minutes in 

 water or sweet whey. If the milk be treated with the solution 

 before the powder is perfectly dissolved the curd will not be uni- 

 form. There are rennet powders in commerce which possess a 

 strength of 1 to 300,000 or even greater. In addition to rennet 

 powders, rennet preservers are also sold in the form of tablets. 



The juices of certain plants, for example, the fig-tree (Ficus 

 Carica), artichoke (Cynara scolimus), some kinds of thistle (for 

 example, the Carlina corymbosa and G. acaulis), the melon-tree 

 (Carica Papaya), withanie (Punceria coagulans), the butter-wort 

 (Pinguicula vulgaris and P. alpina), exert on milk a similar action 

 to that of rennet. The juices of the fig-tree and of some thistles 

 are the only ones of these which in rare cases have been tried in 

 practice. The special rennet used by the Israelites was not prepared 

 from plants, but from the stomachs of calves killed according to the 

 Jewish law. 



