Test for determining casein in milk (Van Slyke and Bosworth).

A given amount of milk, diluted with water, is made neutral to phe-nolphthalein solution by addition of a solution of sodium hydroxid. The casein is then completely precipitated by addition of standardized acetic acid ; the volume of the mixture is made up to 200 cc. by addition of water, thoroughly shaken, and then filtered. Into 100 cc. of the filtrate a standardized solution of sodium hydroxid is run until neutral to phenolphthalein. The solutions are so standardized that 1 cc. is equivalent to 1 per cent of casein when a definite amount of milk is used. The number of cubic centimeters of standard acid used, divided by 2, less the amount of standard alkali used in the last titration, gives the percentage of casein in the milk examined. When one uses 17.5 cc. (18 grams) of milk, the amount used in the Babcock milkfat test, the standard acid and alkali solutions are made by diluting 795 cc. of tenth-normal solutions to one liter. By using 22 cc. of milk, tenth-normal solutions can be used directly ; or by using 20 cc. of milk and tenth-normal solutions, adjustment is made by multiplying the final result by 1.0964.

Wisconsin curd-test.

This curd-test may be of use to creamerymen in detecting milk which is giving trouble on account of odors, taints, gas, and so forth. Sometimes the milk from a certain cow contaminates the milk of the entire herd. In such a case, the dairyman may find this test useful.

Sterilize as near as possible by immersing in boiling water for 30 minutes as many pint glass fruit-jars as there are samples to be tested. Cool the jars at the same time, keeping them covered to prevent contamination. Then fill the jars two-thirds full of the milk to be examined. Set the jars in a tank of water, the temperature of which is about 100° F., and allow the milk to come as near as possible to the temperature of the water in the tank. The temperature of the milk may be taken with a thermometer that has been held for at least one minute in boiling water; the thermometer should be thus treated after taking the temperature of each sample to prevent carrying contamination from one sample to another.

When the temperature of the milk has reached about 95° F. to 98° F., add to each jar of milk about 10 drops of rennet and shake thoroughly. The rennet will coagulate the milk in about 20 minutes, and the whey should then be poured off. The whey will separate more readily from the curd if the latter is broken up with a knife or other instrument which has been dipped for at least one minute in boiling water. As much of the whey as possible should be drawn off. The jars should then be set in the tank and kept at a temperature of about 100° F. for 6 to 8 hours. Examination of odor and condition of the curd may be made every 30 minutes. The condition of the curd may best be told by cutting it with a sharp knife and examining the freshly cut surface for gas pockets.

Great care should be exercised in the entire process to have everything which comes in contact with the milk as near sterile as possible.

458        MILK AND MILK PRODUCTS; DAIRY FARMS

Propagation of Starter for Butter-making and Cheese-making

(Guthrie)

1.  Take three one-quart milk bottles or fruit jars.

2.  Use fresh, clean milk (either whole milk or skimmed milk) which must have a nice flavor.

3.  Fill the containers one-half to two-thirds full of milk.

4.  Protect the containers with regular covers (caps or tops).

5.  Pasteurize by heating to 180°-200° F. for thirty minutes or longer, and then cool to ripening temperature of 60°-75° F.

6.  After pasteurization the milk is ready for inoculation. Inoculate in a quiet place where the wind cannot blow dirt and bacteria into this clean seed bed.

7.  Incubate at about 60°-75° F. The first inoculation from the commercial culture should be incubated at about 70°- 85° F.