THE STORY OF A GRAIN OF CORN. I. MANUFACTURING PROCESSES
Examination of the corn grain discloses certain constituent parts having widely different properties and values. The separation of these components, their transformation into products of increased value, and the development of uses for these manufactured materials are the important functions of the corn products industry. Since the extension of the uses of products manufactured from corn increases the demand for this most important agricultural commodity, and, therefore, must enhance the price received by the corn grower, the mutual interest of the farmer and the manufacturer of products from corn in the fullest development of this industry is beyond question. It is purposed to discuss three phases of this broad subject: Manufacturing Processes, Products and Their Uses, and The National Economic Importance of the Industry. To attempt to cover details of processes in this rather limited discussion would be both impossible and undesirable. It is hoped that the outline presented will give the reader a clear picture of a t least the principles involved. Preparatory Operations The shelled corn received a t the plant is first freed from incidental dirt and foreign material and stored in large reservoirs to be drawn upon as needed. The grain of corn has an exterior covering or integument consisting principally of cellulose. This hull surrounds the endosperm or main portion of the kernel, which consists of a mixture of starch and gluten, nitrogenous material. Within the endosperm and near the apex or pointed portion of the kernel is the germ, containing the oil and some fibrous material. In addition, there are certain solnbles, principally on or near the surface of the grain. The first objective in the process is to separate these various constituents as completely and economically as possible. This separation is accomplished in the main as follows: Steeping The steeps are large cylindrical structures, usually of wood and cast iron, capable of holding 2500 bushels of corn. Warm water containing a small amount of SO2 gas is circulated over the grain until the kernels have become softened. The SOz serves two purposes. It aids in softening and prevents fermentation of the grain a t the temperatures used. The steep water after this operation contains most of the solubles present
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in the corn. This water is concentrated by evaporation and used as an important constituent of the cattle feed.
Crushing, Grinding and Reeling The softened kernels are passed through disintegrators with a considerable amount of water to maintain proper gravity. The whole grain is crushed, but particularly the germs are freed, and due to their lower specific gravity float when the crushed mass is collected in tanks called "germ separators." These germs are removed with surprising complete-
ness by a skimming process. The collected germs are washed, dried, ground and put through expellers to remove the oil. The resulting extracted mass still contains about 10yoof oil which, with the solid matter, becomes a constituent of the cattle feed. Of the oil obtained, the greater part is refined and marketed as edible oil for various food purposes. As crude corn oil, it is suitable for soapmaking and other industrial uses. The magma remaining after the removal of the germs contains the starch, gluten, and fibrous material, cellulose. This mixture is finely ground and passed through various stages of washing and screening (reels)
which accomplish the complete removal of the fibrous cellulose material. This cellulose is collected and dried and finally finds its way to the cattle feed. Tabling The elimination of the cellulose leaves the starch and gluten mixed with water in a cream-colored suspension. This liquor is then allowed to flow over long, narrow, comparatively shallow, and slightly inclined troughs known as tables. Owing to its higher specific gravity, the starch
settles out and collects on the bottom of the tables and the gluten suspended in the water follows the overtlow. The gluten-containing water is collected in large reservoirs in which the gluten is settled out, then filter-pressed and dried. I n this condition, the gluten is incorporated in the cattle feed in proportion to the amount of protein desired. The water from the gluten settlers is returned principally to the steeping process and thus finds its way again through the system. The wet starch on the tables is already in a surprisingly high state of purity. There is, of course, a small amount of gluten and fiber present,
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as well as solubles dissolved in the water retained. Formerly, it was customary to remove this wet starch by shovels and dry in the kilns without further treatment. This product represents the crudest form of starch commercially possible. Today, for the most part, the starch is flushed off the tables with large quantities of water and filter-pressed, which treatment reduces the solubles, and after drying, gives a purer starch. In some cases, the tabling process is repeated to reduce the gluten and fiber content and also the percentage of solubles. The treatment
depends upon the grade of starch desired and the uses to be made of the final product. Thus is obtained the product which may be regarded as the crude material for several important branches of the starch industry.
Starch The starch obtained from the tables, by way of the filter-presses, is sufficiently pure for many purposes and carries about 45% moisture. This moisture is removed by drying in kilns, through which a current of hot air circulates a t carefully controlled temperatures. If the drying
is completed within a few days, the product obtained is a mixture of starch powder, and larger particles usually called "starch crystals." Starch in this form is commonly known in commerce as "pearl starch" and contains from 12.5 to 13.5% moisture. To obtain "crystal starch" the wet starch is usually placed in the kilns in the form of a compact cube and the drying process prolonged, sometimes for weeks. In this way, due to the contraction of the wet mass, irregular lines of cleavage are
DRYSTARCH READYTO BE BROKEN UP
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formed and finally the mass collapses in the form of what may be described as irregular, distorted prisms, called "crystals." Powdered starch is prepared from "pearl starch" by a beating and bolting operation which removes hard, over-dried particles as well as protein matter left over from the tabling process. "Lump s t a r c h is obtained by &eating powdered starch with steam and subjecting the steamed starch to high pressure. This gives a solid cylindrical mass of starch which is crushed and screened to size. Food starches are purified by retabling or washing to meet the requirements of the Pure Food Laws.
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Modified Starches These starches may he regarded as "alkaline thick-boiling starches'' and the so-called "soluble" or "thin-boiling" starches. Alkali in the form of sodium hydrate or sodium carbonate is introduced into the process after tabling in such amount that the starch after drying shall show a slightly alkaline reaction. "Thin-boiling" starches, improperly called "soluble starches" are prepared from ordinary properly purified starch by treatment with extremely
dilute acid, usually sulfuric, a t a predetermined temperature and concentration until the desired modification has been effected. The acid is neutralized and the starch separated and dried in the usual manner.either in "pearl" or "crystal" form. Dextrines, British Gum and Gums These products are produced from starch of proper purity and moisture content. The properties of the final products depend upon these factors as well as the conditions under which the conversion is made. The starch is charged into the "cooker," usually a covered cast iron kettle provided with a stirrer, and heated with a steam jacket, or otherwise. The conversion of the starch may be accomplished by heat alone; however, a small
amount of acid, usually nitric or hydrochloric, is used as a catalyst in connection with a high temperature. The amount of starch converted into water-soluble dextrine or gum, the color of the product, and the pasting properties depend essentially upon the time and temperature of conversion, the amount of moisture, and the amount and kind of acid used. Considerable skill and experience are required in adjusting the various factors and producing uniform products. There is really no sharp distinction between dextrine and British Gum. The latter term was originally applied to products obtained by heat alone without the aid of acid. The term "starch gum" is used very broadly
and covers a great variety of products obtained by the partial or complete dextrinization of starch. Corn Sirup and Corn Sugar In order to make a good grade of corn sirup or corn sugar, a starch of high purity must he used. The process involved is that known to chemists as hydrolysis. The starch, suspended in water, is heated in an autoclave by means of steam in the presence of a small amount of a catalyst. In this country, the catalyst is practically without exception chemically pure hydrochloric acid, the same acid which performs the same function in the process of digestion of starch in the human body. The course and extent of the reaction in the autoclave depend upon time, temperature, pressure,
concentration, and the amount of the catalyst present. That is to say, if a partially converted product represented by corn sirup is desired, certain conditions are observed, while if the final product is to be in the form of crystallized sugar, the conversion is subject to a different control. In any case, the hydrolysis takes place very rapidly and must be carefully controlled. The resulting solutions are free from starch when removed from the converter. The carbohydrates are present as reducing sugars, glucose or dextrose, perhaps some maltose, and non-reducing carbohydrates, intermediate between starch and dextrose, which for the purpose
of analysis are usually spoken of as dextrines. In the manufacture of corn sirup, also commercially, but improperly, called glucose, the conversion is carried to a point where the sirup, when concentrated to its proper gravity, will contain approximately 33% reducing sugar, and about 40y0 non-reducing carbohydrates. In the case of the lower grades of solid sugar, the reaction is carried farther, while when pure crystallized glucose or dextrose is desired, the conversion is as thorough as is consistent with the practical methods of purification. What happens when the conversion isended is very simple. The acid solution is neutralized to the proper fiH value. The precipitate formed a t this point is removed by mechanical filtration. A series of bone char
filtrations for decolorizing, and evaporation follow. In the case of corn sirup (commercial glucose) the concentration is stopped a t the proper specific gravity. Solid sugar is obtained from a properly converted and purified liquor by evaporation to the point where on cooling crystallization occurs. The concentrated solution is poured on a special crystallizing floor and after partial solidification, cut up in large rectangular slabs. These slabs are "cured or "aged to allow the fullest possible crystallization before delivery to the consumer. In this manner the various grades of crude corn sugar for industrial purposes are produced. The so-called "pressed sugars" are obtained from the sugar described by expelling the adhering mother liquor (hydrol) in hydraulic presses. Hydro1 corresponds to the molasses produced in the cane sugar industry. When sugar of the highest pufity is desired, the converted and purified liquor is concentrated to the crystallizing point and crystallized out in crystallizers while in motion, under proper precautions for temperature control in order to obtain the hydrated crystal containing one molecule of water of crystallization, or the anhydrous crystd, and not a mixture of the two forms. The crystals, after centrifugation and washing, will be 99.5 to 99.8% pure dextrose on the dry basis. Naturally, a certain amount of hydrol is eventually obtained from this process of crystallization.
