The cotton plant grows over a wide area in the United States, including all of the southern states and extending into southern Virginia, southern Kentucky, southern Missouri, and Oklahoma. In former years the cotton plant was cultivated solely for its fiber. It is only in the last quarter of a century that the high value of its seed for many purposes has been realized. The seed of the cotton plant is preëminently rich in oil and protein. It contains traces of certain poisonous alkaloids, betain and cholin, the presence of which renders its indiscriminate use for cattle food in some cases dangerous. In the preparation of oil, however, no trace of these poisonous substances is found, since they exist solely in the non-fatty tissues of the seed. The production and refining of the oil has now grown to be a great industry and has already added much to the wealth of the cotton growers and the comfort and nutrition of the people in general.
Magnitude of the Cottonseed Oil Industry.
—The average cotton crop of the United States is about 12,000,000 bales of about 500 pounds each. For every bale of cotton there is produced 1,000 pounds of seed. This would make the average cottonseed crop of the country about 6,000,000 tons. It is estimated that not over two-thirds of this is used in the mills; this would make about 4,000,000 tons. The average yield of 40 gallons to a ton shows the production of crude oil to be 3,200,000 barrels of 50 gallons each. This oil in refining loses on the average about 8 percent, which would leave 2,944,000 barrels of refined oil for edible and other purposes. Not less than two-thirds of this oil is used for edible purposes. A conservative estimate would place the quantity used for food between two millions and two millions and a half barrels per annum. The quantity varies with the prices of other fats.
Cotton seed is brought to the mills from the gins either by rail in box cars or in wagons. On arrival at the mills, it is stored in large sheds, known as seed houses. A single seed house will often contain as much as 5,000 to 10,000 tons. The seed is carried into the mill by means of conveyers. It first goes through coarse screens which remove the greater part of the trash and sand, after which it is passed over magnetized iron plates which remove nails and pieces of iron which may have accidentally gotten into the seed. After the seed is thoroughly cleaned it passes through gins known as linters, which remove from 40 to 50 pounds of short staple cotton known in the trade as “linters.” This cotton is used for preparing cotton batts, mattresses, etc. Conveyers carry the seed from the linters to the hullers, which are rapidly revolving drums covered with cutting knives which chop up the seed. From the hullers the cut-up seed pass over a series of screens where the meats are shaken out while the conveyors carry the hulls to a suitable store house. The hulls are used for cattle food. The meats are carried to the crusher rolls, through which they pass. These rolls break up oil cells to a large extent and leave the meats in a finely divided condition. From the crusher rolls the meats are carried to steam-jacketed kettles provided with agitators. There they are cooked to the proper point, which is determined by feel and smell. From the heaters the meats are dropped into cake formers, where they are formed into shape of cakes between camel’s hair press cloths in which they are placed in the heavy hydraulic presses which press out the oil. Good press-room work will give out 45 gallons of oil to the ton and leave in the cake between 6 and 7 percent of oil.
The crude oil as it leaves the presses varies in color from light sherry to deep claret. The variation is due to local conditions affecting the seed, also the manner of treatment in cooking. The flavor of the crude oil varies greatly in the different parts of the country. That made in Georgia and Carolina has a strong flavor of peanut, while that made in the Mississippi Valley and Texas has more the flavor of sweet Indian corn.
To prepare crude oil for edible purposes, it must go through a process of refining; this is accomplished by agitating in large tanks with caustic soda solution. When the soda is added in the proper amount, the coloring matter, free fatty acids, and vegetable matter contained in the oil are converted into a mucilaginous soap which separates in dark-colored flakes through the oil when heat is applied. When the granulation has reached the proper point, agitation is stopped, and the flaky soap stock settles at the bottom of the tank, leaving a clear, light, greenish-golden oil on top. The best practice allows tanks to settle about 12 hours, after which the soap stock has drawn off and the well settled yellow oil is removed to a settling tank where it is gently heated to remove moisture and remaining soap stock. This produces what is known as prime summer yellow oil. This oil has a sweet flavor and light yellow color. Unfortunately when used for cooking it gives off a very disagreeable odor and leaves a bad flavor in the article of food cooked with it. This renders further purification necessary. The oil is heated to temperatures varying from 150 to 200 degrees F. and agitated in kettles with fuller’s earth, after which it passes through filter presses, which remove the fuller’s earth and leave the oil very nearly white. In this condition the oil is still unfit for cooking purposes, on account of the peculiar flavor given by the fuller’s earth treatment, which is commonly removed by treatment with steam. Details of this deodorizing process vary and are regarded as trade secrets. The oil so prepared is largely used in the preparation of substitutes for lard and similar cooking fats. Such oil is a great improvement over the ordinary summer yellow and bleached oils, but falls short of being an ideal oil.
Within the last few years a cottonseed oil has been put on the market in which the objections to the use of cottonseed oil as food have been as nearly overcome as the chemical nature of the oil will permit. The oil produced by this process is practically odorless and tasteless and can be used satisfactorily for all culinary purposes. Large quantities are used by the bakers in place of lard. (David Wesson.)
Further Details.
—The cotton seed from various sources is put through a screen to take out the bolls and coarse material. The seed is then put through a gin to remove as far as possible any remaining lint, of which about 20 pounds per ton of seed are obtained. The clean seed is next sent to a huller composed of revolving cylinders covered with knives, which cut up both seed and hull. The chips are then conveyed to a screen placed on a vibrating frame, through which the kernels fall. The hulls are carried by an endless belt to the furnaces, where they are burned. The kernels of the seed are conveyed to crusher rolls, where they are ground to a fine meal. The meal is then sent to a heater, where it remains from twenty to forty minutes. These heaters have a temperature of 210 to 215 degrees F.
The hot meal is formed into cakes by machinery; these are wrapped in cloth and placed in the press. About sixteen pounds of meal are put in each cake. The cakes are placed in a hydraulic press, where a pressure of from 3,000 to 4,000 pounds per square inch is applied. The press is also kept warm. The expressed cakes contain only about 10 percent of oil. The cake is sold as cattle food or for fertilizing purposes. The crude oil as thus expressed contains about 1.5 percent of free acid, also a notable quantity of water and solid matters in suspension. The manufacture of cottonseed oil usually takes place in the winter months immediately after the ginning of the cotton is completed. The oil is likely to become rancid if kept unpurified until the hot months. The crude oil is collected in oil tanks at the press and shipped to the refining houses. In winter time when tanks are sent to the north where the temperature is very low the contents of the tank become solid unless protected from the action of the cold.