Foods and Their Adulteration / Origin, Manufacture, and Composition of Food Products; Description of Common Adulterations, Food Standards, and National Food Laws and Regulations

by Harvey Washington Wiley

—There are various forms of tanks used for producing steam rendered lard. In the open kettle there is a jacketed arrangement by means of which steam, at the proper temperature, is made to act upon the contents of the inner kettle. In the closed kettle the steam may be applied in the form of a jacketed arrangement or introduced directly into the kettle. The residues which remain after the steaming is completed and after the lard has been drawn off are withdrawn from the conical lower portion of the kettle which can be opened for the removal of these residues. A typical kettle for rendering lard is shown in [Fig. 10]. The fragments of meat to be received are placed in the opening M which is then properly closed when the tank is full. Steam is admitted and the condensation which is produced at first by the cold contents of the tank is drawn off through a water pipe. After the tank is thoroughly heated and the fat begins to separate the lard will rise above the water and the solid fragments and at the end of the process will fill the upper part of the tank. By means of the cocks at D it can be determined to what depth the tank is filled with lard and the lard can be drawn off through these cocks until water begins to flow. The bottom of the tank at G is then opened and the residues withdrawn, dried and ground for tankage.

Physical Properties of Lard.—Specific Gravity.—

The specific gravity of pure lard is to be determined at some definite temperature, inasmuch as a statement of its specific gravity without some reference to the temperature at which it is determined is likely to be misleading. It is not convenient to ascertain the specific gravity of a lard at a temperature below its melting point. It is customary, therefore, either to take the specific gravity at about 40 degrees C., or at a temperature of boiling water.

The average specific gravity of pure lard at 40 degrees C. (104 degrees F.), regarding water as 100, is 89, and at 100 degrees C. it is 86, the weight of water being determined at the point of greatest density, namely, 4 degrees C. (39 degrees F.). Unfortunately the specific gravity of pure lard is not very greatly different from that of other oils or other fats used in its adulteration. For this reason it is not of the highest value for determining whether or not the pure article has been subjected to adulteration.

Melting Point.

—The melting point of a pure lard is a physical characteristic of great value, since it is chiefly influenced by the part of the body of the animal from which it is made. The fat which is rendered from the foot of the hog has the lowest melting point, namely, about 35 degrees C. (95° F.). The fat adhering to the intestines has the highest melting point, namely, 44 degrees C. (111 degrees F.). The fat derived from the head of the hog has a slightly higher melting point than that from the feet. The kidney fat has a melting point of 42.5 degrees C. (108.2 degrees F.). In the steam rendered lards, representing the average of lards passed upon by the Chicago Board of Trade, the average melting point is found to be about 37 degrees C. (98.7 degrees F.). The melting point of superior or leaf lard has an average value of about 40 degrees C. (104 degrees F.).

Color Reaction.

—A pure high grade lard when mixed on a white porcelain plate with the proper amount of sulfuric or nitric acid should give only a very slight coloration. The production of any considerable quantity of color, either brown or black, indicates the presence of organic impurities in the lard.

Rise of Temperature with Sulfuric Acid.

—The various fats give different degrees of heat when mixed, under certain conditions, with strong sulfuric acid. It is possible to determine the approximate degree of the adulteration of lard by applying this test. The operation is a simple one and is conducted in the apparatus shown in [Fig. 11]. A common test tube about 24 cubic centimeters in length and 5 cubic centimeters in diameter is hung as indicated in the figure, provided with a stopper carrying a thermometer in the center with a bent glass rod stirrer passed loosely through the stopper on the side and a funnel for the introduction of the acid on another side of the thermometer. A coil which is on the stirring rod is so arranged as to permit the bulb of the thermometer to pass through its center.