Yeast will then be added to the mash to ferment the sugars to ethanol and carbon dioxide. Using a continuous process, the fermenting mash will be allowed to flow, or cascade, through several fermenters until the mash is fully fermented and then leaves the final tank. In a batch fermentation process, the mash stays in one fermenter for about 48 hours before the distillation process is started. The mash will then be pumped to the continuous flow, multi-column distillation system where the alcohol will be removed from the solids and the water. The alcohol from the top of the column will then pass through a dehydration system where the remaining water will be removed.
Most ethanol plants use a molecular sieve to capture the last bit of water in the ethanol.
Carbon dioxide is given off in great quantities during fermentation and many ethanol plants collect that carbon dioxide, clean it of any residual alcohol, compress it and sell it for use to carbonate beverages or in the flash freezing of meat. Distillers grains, wet and dried, are high in protein and other nutrients and are a highly valued livestock feed ingredient. Ethanol production is a no-waste process that adds value to the corn by converting it into more valuable products. Ethanol is also made from a wet-milling process. Many of the larger ethanol producers, such as Minnesota Corn Processors, use this process, which also yields many other products, such as high fructose corn sweetner.