ENZYMES. 85 
69. Galactase. 
Babeock and Russell in 1897 described an enzyme in milk 
to which they gave the name galactase. When milk is rendered 
sterile by chloroform, it will curdle upon standing as if it con- 
tained rennet, and the casein will be digested, that is, it is 
changed to soluble peptones. Galactase is killed at a tempera- 
ture of 180° F. Its optimum temperature is about 100° F. It 
is believed that this enzyme is at least the major cause of the 
breaking-down of the casein in cheese and its change into soluble 
peptones and is therefore a most important factor in the ripen- 
ing of Cheddar cheese. 
7o. Rennet Extract. 
Since early times an extract from the calf’s stomach has 
been used to curdle milk in the manufacture of cheese. Such an 
extract is supposed to contain two enzymes, one, rennin, having 
the property of coagulating the milk, and the other, pepsin, 
which afterwards digests the curd. 
71. Rennets, Where Obtained. 
Commercial rennet is the stomach of new-born calves 
which are slaughtered before beimg fed; the stomachs are 
cleaned and dried, before they are marketed. 
The best rennets come from Bavaria; it is stated that the 
City of Copenhagen alone consumes annually 5,000,000 rennets 
in the manufacture of rennet extract. Cheese makers used to 
buy the rennets and make their own extracts as needed, and the 
majority of Swiss cheese makers do so now, but extracts, pow- 
ders and tablets are now manufactured on an extensive scale, 
and are much more uniform and reliable than the old home- 
made extracts, which are likely to vary greatly. 
The preparation of rennet powder is too complicated a pro- 
cess for a cheese maker to follow, but one can make his own 
extract for the season, if he wishes, as follows: 
72. How Rennet Extract Is Made. 
Prepare a sufficient number of rennets, say five hundred, 
by splitting them open so that the water can get into them. 
Then place the rennets in an oak barrel and fill it with water 
