INTRODUCTION
Wet Milling

Wet milling is a process that requires use of high quality (U.S. No. 2 or better) corn that fractionates the corn kernel to produce numerous products intended for human use. Fresh water enters the milling system in the final stage of starch washing. Subsequently, it runs countercurrent with respect to the flow of corn, passing through numerous screens and separating implements, acquiring soluble nutrients at each step. Ultimately, this solution will serve as the resource in which corn entering the process will be initially steeped. Lactic acid-producing bacteria in the steeping process ferment the soluble carbohydrates collected by the water to further kernel softening. Following the steeping process (Figure 1), corn kernels are separated into kernel components of corn bran, starch, corn gluten meal (protein), germ, and soluble components. If the wet milling plant is fermenting starch into ethanol, a portion of the steep water (now called steep liquor) is added to the fermentation vats to supply nutrients for the ethanol-producing yeast cells to grow. The ethanol is distilled off after the fermentation process. The solution exiting the still is called distillers solubles, not to be confused with dry milling distillers solubles. This product contains very little corn residue, almost no fat, and is high in protein from the remnants of yeast cells from the fermentation process.The distillers solubles and a portion of the steep liquor are added to the bran fraction of the corn resulting in WCGF. The WCGF can have a portion of the germ meal added if the plant has those capabilities. For a more complete review of the wet milling process, the reader is referred to Blanchard (1992). The actual composition of WCGF can vary depending on the plant capabilities. Steep, a combination of steep liquor and distillers solubles, contains more energy (136% the feeding value of corn) and protein than corn bran or germ meal (Scott et al., 1997).Therefore, plants that apply more steep to corn bran or germ meal will produce WCGF that is higher in crude protein (CP) and energy.

WCGF contains 16 to 23% CP, which is approximately 70% ruminally degradable protein (degradable intake protein, DIP) used by rumen microbes. During wet milling, corn gluten meal is removed and marketed in higher value markets. Corn gluten meal should not be confused with WCGF, as corn gluten meal contains approximately 60% CP that is 40% DIP and 60% bypass protein (undegradable intake protein, UIP).

For more information or to request additional copies of this manual, contact the Nebraska Corn Board at 1-800-632-6761 or e-mail k.brunkhorst@necorn.state.ne.us.

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For more information on the feeding of corn milling co-products to beef cattle
and information contained in this manual, contact:
Dr. Galen Erickson, University of Nebraska-Lincoln, Department of Animal Science Room C220, Lincoln, NE 68583-0908, 402-472-6402

Date published: August, 2007