Page:The story of milk.djvu/46

 There are other tests used in scientific dairying as the Fermentation Test to ascertain the relative purity of milk, the Casein Test, etc., but the above are those mostly used besides the Bacterial Count which is mentioned under the chapter on "Milk Supply," and the Rennet Test described under "Cheese Making." FERMENTS Two classes of ferments are of importance in connection with milk: (1) "unorganized" or chemical ferments, the "enzymes," and (2) "organized" ferments such as bacteria and yeast. Enzymes

Rennet.—Among the unorganized ferments, Rennet or Rennin is highly important on account of its power of coagulating or curdling milk by precipitation of the casein. Rennet is extracted from the stomach of the suckling or milk-fed calf, where it serves in digesting the calf's food. It is in the market in the form of a liquid extract as well as a dry powder compressed into

drops of the alkali are added and stirred in several times until a faint but distinct pink color remains for some time. That indicates that the acid in the milk has been neutralized and the amount of the soda solution consumed is then read off on the scale on the burette. By dividing the number of c.c. of the soda solution used by two, the tenths per cent of lactic acid in the milk is found. For example, if it takes 4 c.c. of the soda solution to neutralize 17.6 c.c. milk, the acidity is .2%. This depends upon the fact that 1 c.c. of a tenth normal soda neutralizes .009 gram of lactic acid and that therefore the per cent of acid in the milk is equal to .009 multiplied by the number of c.c. of soda solution used, divided by the number of c.c. of milk and multiplied by 100.
 * [Footnote: pink. The color will quickly disappear, however, and a few more

If 50 c.c. of milk is taken instead of 17.6 the calculation is changed accordingly.]