Plants that produce ethanol, corn oil, and corn sweeteners also produce by-products in large quantities, and these by-products are employed successfully by beef producers as a more affordable feed alternative for cattle.
Wet Milling Process
The wet milling process is a complex one, producing a variety of products and by-products. Simply put, corn is steeped for 30-40 hours to begin the process of breaking the kernel down into its components. The germ is separated for the extraction of corn oil. The bran is then screened, and the starch is separated from the gluten. The steepwater is condensed to the consistency of molasses and mixed with corn bran to produce corn gluten feed.
Wet Milling Co-products
Corn Gluten Feed Corn gluten feed is the highest volume co-product of the wet corn milling industry and is a popular feedlot cattle protein and energy source because it is an intermediate protein product that is rich in highly-digestible fiber. Dry corn gluten feed is often pelleted and marketed to domestic and European dairy industry. Corn gluten feed actually contains no gluten, but a mixture of corn bran and condensed steepwater solubles; it may also contain corn germ meal, as well as other co-product streams from the plant. Corn gluten feed can vary in composition due to the ration of condensed distillers solubles to corn bran. This will vary from plant to plant, depending on the markets available. Corn gluten feed that is higher in bran will be lower in protein, phosphorous, and sulfur.
Corn Gluten Meal Corn gluten meal is golden-yellow and is mainly gluten, the high protein portion of the corn kernel. Corn gluten meal is used primarily in the swine and poultry industries and is high in xanthophyl, a yellow pigment. Corn gluten meal is a high bypass protein source. Although expensive, it may be useful in beef diets that require bypass protein, such as those for lightweight calves.
Condensed Steepwater Solubles Condensed steepwater solubles are an excellent source of soluble protein for liquid beef supplements. Most condensed steepwater solubles are used in corn gluten feed, but because condensed steepwater solubles have the consistency of molasses, they can also be used in liquid supplements. Condensed steepwater solubles are about 35% protein and can be extremely high in phosphorous and sulfur. In 1999, the wet corn milling industry used 1.4 billion bushels of corn (14.8% of the U.S. supply). Wet milling yields 31.5 pounds of starch with corn being processed into 33 pounds of sweetener or 2.5 gallons of ethanol. Also, 13.5 pounds of gluten feed, 2.5 pounds of gluten meal, and 1.6 pounds of corn oil are produced. In 2000, 10.6 billion pounds of corn gluten feed and corn germ meal were produced.
Dry Milling Process
Corn is nearly two-thirds starch, the primary substrate for alcohol fermentation, so the nutrients in the remaining one-third of the corn kernel are concentrated into distillers feeds. The process begins by grinding the grain; starch must be converted to sugar by enzymes before the yeast can ferment the sugar to produce ethanol and carbon dioxide. The fermentation process takes 40-50 hours. The ethanol is collected and refined, and a centrifuge separates the distillers grains from the solubles, which can then be condensed to about 30% dry matter (condensed distillers solubles). These wet co-products can then be used locally for livestock feed or the produce distillers dried grains, or distillers dried grains with solubles. The dried grains can be transported longer distances, but some feeding value may be lost, and drying is expensive.
Dry Milling Co-products
Distillers Grains Wet distillers grains and distillers grains with solubles contain the remaining nutrients after the corn starch is fermented to alcohol, which means that the original nutrients in the corn are concentrated approximately three times. Wet distillers grains are higher in both protein and energy than corn gluten feed (gluten and oil remain in distillers grains). When distillers grains are dried, however, they do lose some energy value when compared to wet products. Like corn gluten meal, dried distillers grains are a good bypass protein source for cattle.
Condensed Distillers Solubles Distillers solubles can be added to the distillers grains, or condensed and used as a liquid cattle feed supplement. Condensed distillers solubles appear to be slightly higher in energy and similar in protein to wet distillers grains when adjusted for moisture. The protein level is similar to distillers grains (approximately 30%). Because condensed distillers solubles are 70% moisture, upper Midwestern feeders should use heated or underground tanks to prevent freezing.