Ethanol is produced from starch. All agricultural crops and residues contain starch, which is a polymer of glucose, a six-carbon sugar. To produce ethanol from grain, the starch portion of the grain is exposed and mixed with water to form a mash. The mash is heated and enzymes are added to convert the starch into glucose.
The next phase, fermentation, involves the addition of yeast to convert the glucose to ethanol and carbon dioxide. Fermentation produces a mixture called "beer," which contains about 10 - 15 percent ethanol and 85 percent water. The "beer" is then boiled in a distillation column to separate the water, resulting in ethanol. Ethanol production from grain utilizes only the starch.
A variety of highly valued feed co-products, including gluten meal, gluten feed and dried distillers grains, are produced from the remaining protein, minerals, vitamins and fiber and are sold as high-value feed for livestock. In addition to grain, ethanol is also produced today from wood waste, cheese whey, waste sucrose, potato waste, brewery waste, and food and beverage wastes. Many ethanol producers capture carbon dioxide emissions for processing and use in beverages.
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