Composition of Cheese. 
63 
Result : Tho curd separated in ^ hour, l)ut not so perfectly 
as in the precedin"; experiment, and in a softer condition. 
The wliey was nion; milky in appearance, and stron<rly 
alkaline. Examined after 24 hours' stand inj»-, it was 
found to be neutral ; after a lapse of 2 days, it was acid. 
Even a considerable quantity of an alkali, therefore, does not 
prevent the coagulation of milk by rennet. 
16//i Exp. — To another pint of milk I added an unwcighed 
quantity of potash heated to 84°, and then J ounce of 
rennet. 
Result ; No coagulation took place. 
Much more alkali was used in this experiment than In the two 
preceding ; an excess of alkali, therefore, prevents the separation 
of curd by rennet. 
17//i Exp. — To some milk, sufficient tartaric acid was added to 
make it distinctly acid. 
Result : No coagulation took place in the cold. On the appli- 
cation of heat, the milk coagulated but imperfectly. 
\%th Exp. — To another portion of milk I added a good deal of 
tartaric acid. 
Result : The milk coagulated after some time, but imper- 
fectly ; on raising the temperature, more curd fell down. 
In order to precipitate the casein from milk by tartaric acid, 
it is thus necessary to add a very large excess of acid, and at the 
same time to raise the temperature of the milk. 
These experiments prove thus — 
a. — That the action of rennet on milk is not the same as that of 
an acid, inasmuch as rennet coagulates new milk without 
turning it sour in the least degree. 
h. — ^That rennet can precipitate curd from milk, even when pur- 
posely made alkaline. 
c. — That the whey of milk, when produced from perfectly sweet or 
neutral milk, is at first perfectly sweet or neutral, but rapidly 
turns sour. If made from milk having an alkaline reaction, 
the whey at first is alkaline ; when from milk slightly acid, 
the whey likewise is slightly acid. 
d. — That rennet ceases to coagulate milk at about 135°, and 
upwards. 
e. — That the action of rennet upon milk is more energetic when 
the milk is slightly acid. This, perhaps, is the reason why 
some persons recommend putting some sour whey into the 
milk before or after adding the rennet. 
f. — That an excess of alkali prevents the coagulation of milk by 
rennet. 
