The Book of Cheese

by Charles Thom; W. W. Fisk

1 scales sensitive to 0.01 gram

1 set of weights, 0.01 to 100 grams

The body of the copper drying cup may be made in two parts. One of the parts is a jacket that forms the outer wall of the apparatus. It has a flat bottom 4½ inches in diameter, and the perpendicular wall is 4½ inches in height. The inner part of the cup must have a flat bottom 2¾ inches in diameter and a side wall 3¾ inches high. A flange attached to the upper rim of the inner part extends out at right angles to the cup wall and forms a cover for the space between the walls when the two parts are put together. The flange is bent down around its outer edge to make it fit snugly over the upper rim of the outer jacket. It thus holds the inner cup securely in place, leaving a space about ¾ inch wide for oil between the walls and bottoms, and permits the apparatus to be taken apart readily. A circular opening about ½ inch in diameter is made through the flange to permit the insertion of a thermometer for taking the temperature of the oil or the melted fat which is used in the space between the walls. Lard or tallow serves best for use in this space; a readily inflammable oil should not be employed. The thermometer may be permanently held in place by passing it snugly through a hole bored in a cork, the cork being then fitted into the hole through the flange. A flat metal cover is placed on the cup when making a test. This cover has a hole through the center just large enough to permit the neck of the drying flask to extend up through it. The cover assists in keeping the body of the flask at a constant temperature by preventing the entrance of cold air currents. The thermometer should register changes in temperature between zero and 200° C. The alcohol lamp should yield a flame about ¼ inch in diameter and ¾ inch high. The tripod should be about 6 inches high and of proper diameter at the top to support the oil bath.

An ordinary flat-bottom glass Erlenmeyer flask, of such a diameter as to fit neatly into the oil-bath cup, may be used to hold the cheese during the drying operation; but a special glass flask serves better. It is made with a flat bottom 2½ inches in diameter, which will fit into the cup of the drying apparatus. The side walls of this flask should be perpendicular for about 1 inch, when they should begin to slope in toward the base of the neck, which should be located about 2 inches above the bottom. The neck of the flask should be 1 inch in diameter, with perpendicular walls, and its length should give the flask a total height of 4¾ inches. When the apparatus ([Fig. 73]) is put together for the first time, the melted fat or oil may be placed in the outer jacket and the inner cup may then be fitted into position, or the parts may be put together first and the oil then poured into the space between the cup walls through the opening where the thermometer is to be placed. The oil should fill the space to within an inch of the top. The cork through which the thermometer has been passed is then fitted into the opening. The thermometer bulb should be placed in the oil about half an inch above the bottom of the outer jacket. The apparatus is then placed on the tripod over the alcohol lamp. A flame ½ inch in diameter and ¾ inch high will give sufficient heat to hold the bath at the proper temperature. The temperature may be regulated by raising or lowering the lamp or by changing the size of the flame by adjusting the wick. Hundreds of tests may be run without taking the apparatus apart or changing the oil. The copper drying cup can be made by any tinsmith. The other parts may be ordered through any dairy or chemical supply company.

Fig. 73.—Apparatus necessary to test cheese for moisture.

In operating the test, the alcohol lamp is first lighted, so that the oil bath may be warming while the test sample is under preparation. A representative sample of the cheese, which may be taken with a cheese-trier and held in a glass-stoppered sample jar, is then cut into particles about the size of kernels of wheat without removing it from the jar. This may be accomplished with an ordinary table knife that has had the end squared and sharpened. The clean dry flask is then accurately balanced on the scales and a 5-gram weight is placed in the opposite scale pan. Particles of cheese from the prepared sample are put into the flask until the scales comes to an exact balance. Great care should be taken to avoid loss of moisture from the cheese in the preparation of the sample.

With the thermometer in the oil bath registering between 140° and 145° C. (or between 284° and 293° F.), the flask is placed in the cup of the oil bath and the flat disk-shaped cover is adjusted over the apparatus. The flask should remain in the bath for fifty minutes, the temperature being kept between 140° and 145° C. all the time. The flask is then removed, covered and allowed to cool to room temperature in a dry place. It is then weighed, and the quotient obtained by dividing the loss in weight by the original weight, multiplied by 100, gives the percentage of water in the cheese. The following shows the method of computation:

Problem: Five grams of cheese was heated until the water contained in it was evaporated. The remaining substance weighed 3.15 grams. What percentage of water did the cheese contain?