For testing skim milk and cream special forms of test bottles are used—which are described in the circulars coming with the testers and students who desire fuller information are referred to Farrington and Woll’s “Testing Milk and its Products,” published by the Mendota Book Co., Madison, Wis.
[3]. The Acid Test depends upon what in the laboratory is called “titration” and makes use of a “burette,” a long, graduated measuring tube provided with a pinch-cock. This burette is filled with an alkali solution of known strength, usually a “tenth normal” solution of caustic soda. A certain amount of the milk to be tested is measured off into a glass or a white porcelain cup. As a 17.6 c.c. pipette belonging to the Babcock test usually is at hand, that may be used for this purpose. A few drops of an Indicator is added to the milk and under constant stirring the soda solution is allowed to drip into it until suddenly it turns pink. The color will quickly disappear, however, and a few more 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.
If 50 c.c. of milk is taken instead of 17.6 the calculation is changed accordingly.
[4]. Farmers’ Bulletin No. 602, U. S. Dept. of Agriculture.
[5]. Butter Color is made of the coloring matter of “Annatto” dissolved in a refined vegetable (salad) oil. The Annatto tree (Bixa Orelana) grows in the tropics and the seed which has a thin coating of this beautiful coloring matter comes mostly from the West Indian Islands, Jamaica, Porto Rico and Guadeloupe. It is perfectly harmless and is used by the natives to flavor and color soup and other foods much as we use tomatoes.
[6]. The Marschall Rennet Test consists of a graduated cup (a) with a fine hole for an outlet in the bottom. One cubic centimeter of a standard rennet extract is diluted with water in the glass bottle (c). The cup is filled with milk and placed on the corner of the cheese vat, the milk being allowed to run through the fine hole in the bottom of the cup. The moment the surface of the milk reaches the upper mark of the graduation in the cup the diluted rennet extract is added and quickly stirred into the milk with the spattle (d).
When the milk begins to curdle it stops running out. The sweeter the milk is the more will run out before coagulation stops it and the mark on the scale at which it stops indicates the degree of acidity or ripening. The point is to have the milk alike every day and if, for instance, the cheesemaker has found that his cheese is best if he adds the rennet to the milk in the vat when the test shows 2½, he wants to ripen the milk to that degree every day. So, if the test shows 3 or 4, it indicates that the milk is not sufficiently ripened and it should be allowed to stand warm for a longer time before it is set with rennet.
[7]. The Acidemeter for making an Acid Test is described in Chapter [I].
[8]. Rennet (see under “Ferments” in Chapter [I]) is prepared from the third division of the stomach of the suckling or milk-fed calf. Fifty years ago cheesemakers used to make their own rennet by soaking salted calves’ stomachs in sour whey, and our grandmothers used a piece of a dry, salted stomach to make Junket or “Curds and Whey.” About 1868, Christian Hansen, of Copenhagen, Denmark, began the preparation of Commercial Rennet Extract which soon supplanted the home-made rennet in all countries wherever cheese was made. Nowadays rennet in liquid or powder or tablet form for cheesemaking, and Junket Tablets for milk puddings, are prepared pure and of known strength in laboratories and handled by druggists and dealers in dairy supplies.
The fresh stomachs are saved by the farmers or butchers and are either blown up and dried in the air protected from sunlight and rain, or split lengthwise and spread out flat and salted on both sides.