Corn Milling: Wet vs. Dry

Posted by AMG on November 13, 2013

Corn Milling

Approximately 20% of the annual corn harvest is currently used by industrial corn processors to produce a variety of products such as sweeteners, starches, oils, ethanol and animal feeds. The great majority of the remainder is fed to livestock, poultry & fish. This versatile grain is comprised of four components that make manufacturing of a variety of products possible. Corn’s components are Starch (61%), Corn oil (4 %), Protein (8%) and Fiber (11%) – approximately 16% of the corn kernel’s weight is moisture.

Corn wet milling and dry milling are the predominant methods of processing and each method produces distinct co-products.

The Corn Wet-Milling Process

The Corn wet-milling process is designed to extract the highest use and value from each component of the corn kernel. The process begins with the corn kernels being soaked in large tanks called steep tanks in a dilute aqueous sulfur dioxide solution. The softened kernel is then processed to remove the germ which is further processed to remove the high-value corn oil. The Germ Meal remaining after the oil is extracted and marketed for animal feed use.

Following germ removal, the remaining kernel components are screened to remove the fiber. The fiber is combined with the evaporated, concentrated and dried steep liquor and other co-product streams to produce Corn Gluten Feed. The starch and gluten protein subsequently pass through the screens and the starch-gluten slurry is sent to centrifugal separators where the lighter gluten protein and the heavier starch are separated. The gluten protein is then concentrated and dried to produce Corn Gluten Meal, a 60% protein feed.

Some of the starch is then washed and dried or modified and dried. These starch products are marketed to the food, paper, and textile industries. The remaining starch can be processed into products such as sweeteners or ethanol. An average bushel of corn yields 31.5 lbs. of Starch, 12.5 lbs. of Gluten Feed, 2.5 lbs. of Gluten Meal and 1.6 lbs. of Corn Oil.

While the wet milling process is capital intensive with higher operating costs, the ability to produce a variety of products can be valuable in dealing with volatile markets. The wet milling process results in slightly lower ethanol yields than a traditional dry milling process since some of the fermentable starch exits the process attached to the saleable co-products.

The Corn Dry-Milling Process

The corn dry milling process is a less versatile, less capital intensive process that focuses primarily on the production of grain ethanol. In this process the corn kernels are hammer milled into a medium-to-fine grind meal for introduction to the ethanol production process. The products of a traditional dry grind ethanol facility are fuel ethanol and Dried Distillers Grains (DDG), a low-value animal feed product.

In recent years, dry fractionation processes have been introduced following the hammer milling operation in an effort to generate income from higher-value co-products. Various processing operations have been introduced to remove non-fermentable components of the corn kernel with varying degrees of success. These dry fractionation efforts always result in co-products with less purity than those produced by the corn wet milling process. Consequently the ethanol yield from a dry grind / dry fractionation process is negatively impacted as the result of fermentable starch exiting the process with the co-products.

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AMG, Inc., partnering with Quality Technology International, Inc., have combined their fractionation technology efforts to form QTI-AMG, LLC, to develop the Short Path Frac Germ Wet Milling Process (patent pending). The SPFGWM process provides the capability to cost effectively separate and enhance the quality of dry fractionated germ increasing co-product value and returning previously lost fermentable starch to the ethanol process to enhance ethanol yield.

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Topics: All Posts, Corn Milling

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