46 CHEESE MAKING. 
97- Soluble Calcium Salts Required for Rennet Action. 
It has been previously stated that the soluble salts of cal- 
cium must be present in the milk or the rennet will not act (4). 
Fill a Babeock pipette with rennet extract, add three or 
four drops of phenolphtalein solution and titrate with 4 
alkali. 
Experiment (a). Make a rennet test of a sample of milk. 
Add a small quantity of a dilute solution of calcium chloride 
(CaCl,) to the milk and make another test. The coagulation 
will be accelerated. How much? 
Experiment (b). Heat a portion of the sample of milk to 
190° F. for ten minutes, cool it down and make a test. It will 
not coagulate, for the calcium salts have been rendered insoluble 
by the heat. 
Experiment (a). Make a rennet test of a sample of milk. 
add 25 ¢. e. of a strong solution of ammonium oxalate, and make 
a rennet test. It will not coagulate because the soluble calcium 
salts have been changed to insoluble calcium oxalate. 
98. Effect of Milk Preservatives. 
There is a very pernicious practice among some dairymen 
of using antiseptics to keep milk from souring. Among them 
are preservaline (boracic acid) and formaldehyde solutions sold 
under the name of formalin, freezene, etc. These substances not 
only check the necessary bacterial fermentations in the manu- 
facture of the cheese, but affect the rennet action. 
Experiment (a). Make a rennet test of a sample of milk. 
Then add 1 per cent of boracic acid to the sample and make a 
rennet test. Try varying quantities of the boracie acid. 
Experiment (b), Make a rennet test of a sample of milk 
and then add 1 per cent of formaldehyde solution to the milk 
and make a test. Try it with one-tenth of 1 per cent of formal- 
dehyde in the milk. 
Question: Should milk adulterated with preservatives be 
accepted at a cheese factory in view of the preceding results? 
99. Scale Pepsin Compared with Rennet. 
Dissolve four grams of scale pepsin in 100 ¢«. e. of eold 
water. Now make rennet tests with this on milks of varying 
