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Corn Milling Process

Dry corn millers process corn in one of three ways: (1) a tempering degerming process; (2) stone-ground or nondegerming process; or (3) alkaline-cooked process. However, each miller has his own unique variations on the overall processing system.

The most common process is the “tempering-degerming.” The first step in this process is to dry clean the corn, separating fines and broken from the whole corn. Occasionally wet cleaning follows to remove surface dirt, dust and other matter. The clean corn is tempered to 20 percent moisture. While moist, the majority of the outer bran or pericarp, germ, and tip cap are removed, leaving the endosperm. The bulk of the corn endosperm, known as the “tail hominy fraction,” proceeds through the degerminator, is dried, cooled, and sifted. A portion of this “fraction” is isolated as large flaking grits. Further separation is accomplished using roller mills, sifters, grinding tables, and aspirators so that an infinite variety of smaller grits, meals and flours can be produced.

The bran and germ “fractions” are passed through another part of the degerminator as the “through stock” stream. This stream is dried, cooked, and aspirated to remove the bran. Further processing separates the germ from any remaining endosperm. The “through stock” produces crude corn oil; hominy feed; bran products; standard meal; and prime grits, meals, and flours.

Whole ground or stone-ground mills most often use white corn to make food products such as hominy grits and corn meal. These products are essentially whole ground corn with very little of the hull and germ removed.

In the alkaline-cooked process, the corn is cooked in a boiling lime solution for 5 to 50 minutes depending on its intended use then steeped for 2 to 12 hours. The cooked and steeped corn is washed to remove excess alkali and the loose pericarp tissue. The resulting corn product is ground to form the popular masa flour.

About 65 percent of the corn processed emerges as prime products and 35 percent as by-products.

Product Uses

The coarsest product coming from the degerming process is grits, ranging in size from coarse to fine. The coarsest flaking grits, also known as hominy grits, are used for the manufacture of corn flakes. Other sizes of grits are sold separately or as a blend to the makers of breakfast cereals and snack foods and to brewers as brewers grits.

A more finely ground product than girts, corn meal is used to produce corn bread, muffins, fritters, hush puppies and spoon bread. It is also used as an ingredient in products such as corn meal mixes, cereals, bakery mixes, pancake mixes, and snacks.

A finer granulation of corn meal is sold as corn cones which are used in many bakery mixes; breakfast cereals; and as dusting meal for pizzas, English muffins, and other similar products.

Three corn meal products are also purchased by the U.S. government for distribution under its food donation program (P.L. 480): regular corn meal, soy fortified corn meal and corn soy blend (CSB). The products are intended to provide nutrition in the form of both calories and high-quality protein and contain varying amounts of corn meal as the basic ingredient.

The finest granulation of the dry corn milling process is corn flour. Corn flours are used in many dry mixes such as pancakes, muffins, doughnuts, breadings, and batters. Other uses include coatings, baby foods, meat products (as a filler and binder), cereals, and as a fermentation substrate.

The increased popularity of Mexican foods throughout the United States has created greater demand for tortillas and corn-based snack foods. A variety of masa flours are formulated by the alkaline-cooked process, each intended for a specific use. Masa dough can also be made from a mixture of corn flour and water. The masa is then used to prepare flat tortillas or used in the production of corn chips, tortilla chips, taco shells, tostados, and other snack items.

Two food products derived from the “through stock” portion of the milling stream are corn germ flour and corn bran.

The extracted germ cake can be ground and dried to yield a high quality food grade corn germ flour which is high in protein and is an excellent source of minerals. Corn germ flour is available on a limited basis for consumer food products.

Corn bran, an excellent source of dietary fiber, is becoming more important as an ingredient in the manufacture of corn bran cereal.

A small portion of the endosperm gets into the “through stock.” However, it is isolated from the “through stock” and processed in the same way as the main portion of the endosperm to produce prime grits, meals, and flours.

Crude corn oil is expelled or hexane-extracted from the germ. Dry millers get about .7 pounds of crude oil from one bushel (56 pounds) of corn via the expelled process and about 1.25 pounds of crude oil per bushel when hexane-extracted. The crude oil is then sold for further refining into edible oil.

The oil-extracted germ cake, bran, standard meal, and broken corn are generally combined, dried, and ground into hominy feed. As the major by-product of the dry corn milling process, hominy feed is used as an inexpensive, high-fiber, high-calorie ingredient in animal feed.

The less considered industrial uses of dry corn milled products have, in fact, been a growing part of the dry milling industry. Corn flours and chemically modified corn flours provide an inexpensive starch source used in making a variety of industrial products including insulation or fiber board, plywood and related laminating adhesives, compression-molded particle board, and wafer board. They are used for dry wall or gypsum board binders, foundry binders, and as the adhesive or binder in the production of charcoal briquettes.

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