36 CHEESE MAKING, 
until the rennets are well covered. No more water than is nec- 
essary to dissolve the ferment should be used. 
A little salt should be added to the water, say three pounds 
of salt to one hundred pounds of water. The rennets should be 
stirred vigorously every day, to facilitate the solution of the fer- 
ment, and at the end of a week the liquid should be drawn off 
and the rennets wrung out with a clothes-wringer. They should 
be put into water again and soaked for another week, and the 
same operation repeated. As a usual thing, the ferment has not 
all been extracted from the stomachs till they have been soaked 
for four weeks. The liquid that has been obtained by soaking 
the rennets should be filtered through clean straw, charcoal and 
sand, and then an excess of salt added to preserve it. 
The extract should be clear though of a dark color. The 
first sign of the decomposition of rennet extract is a muddy 
appearance. 
If extract is prepared by the cheese-maker, enough to last 
the whole season should be made in the spring when the weather 
is cool; the extract should be kept in a cool place. 
73. Reliable Brands to be Preferred. 
The surest way of getting extract that can be depended on 
is to buy some reliable brand. 
The practice of preparing extract every few days is not to 
be recommended as the strength of the different lots will vary 
and it will therefore not be possible to make cheese that will cure 
evenly. The use of whey as a solvent for the rennet is not ad- 
visable, because other ferments are introduced in the whey. 
The comparison of extracts and their relative value wil: be 
taken up after the rennet test has been explained. 
74. Effect of Heat on Rennet. 
Rennet will not curdle milk at a very low temperature, but 
as the temperature is raised it will begin to work and act with 
increasing rapidity until at a point above 100° F. it is injured. 
By putting cold rennet into warm milk it may work faster up 
to 120° or 130° F., but when the rennet in weak solutions is 
heated to 105° F. it begins to be weakened. A strong solution 
may be held at 150° for fifteen minutes without being entirely 
