CHAPTER V. 
THE DEPORTMENT OF RENNET. 
89. Experiments in Rennet Action. 
In order that the student may better comprehend the de- 
portment of rennet under different conditions, we shall briefly 
state the effect of the various conditions to which it may be sub- 
jected, and give some experiments with the apparatus used in 
the Monrad test, that will enable the student to become familiar 
with the action of rennet under varying conditions. 
go. Effect of Acid and Alkali. 
Acid in the milk accelerates and alkali retards coagulation. 
Experiment (a). Make a test of a sample of milk with the 
Monrad rennet test, observing carefully all conditions as to tem- 
perature, strength of rennet, ete. Record the result in your 
notebook. Now add a small quantity of dilute hydrochloric acid 
to the milk, being careful to stir this constantly while slowly ad- 
ding the acid. If in a laboratory where decinormal solutions of 
acid and alkali are available, use about 25 c¢. ¢. of hydrochloric 
acid to a quart of milk, and note the number of seconds required 
to coagulate the milk, carefully observing all of the conditions 
for making a test properly. 
Experiment (b). Repeat the experiment with an increased 
quantity of acid added to the milk. 
Experiment (c). Add slowly a small quantity of dilute 
soda lye, being careful to stir the milk while adding it, and then 
make a test as before. Keep careful notes in your notebook. 
Experiment (d). Make a rennet test of a sample of milk 
and set it where it will remain warm. Make tests half an hour 
or an hour later and note the time required for coagulation. 
The shortening in the time required is due to the ripening of the 
milk; the bacteria present have been changing the milk sugar 
into lactic acid. 
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