The high temperatures reduce bacteria levels in the mash. Using a continuous process, the fermenting mash is 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 is pumped to the continuous flow, multicolumn distillation system where the alcohol is removed from the solids and the water. The alcohol from the top of the column passes through a dehydration system where the remaining water is removed.
Most ethanol plants use a molecular sieve to capture the last bit of water in the ethanol.
CO 2 is given off in great quantities during fermentation. Wet and dried distillers grains are high in protein and other nutrients and are highly valued livestock feed ingredients. Ethanol production is a no-waste process that adds value to the feedstock by converting it into more valuable products. Ethanol is also made from a wet-milling process. Many larger ethanol producers use this process, which also yields products such as high-fructose corn sweetner.