Ethanol Production Process

Ethanol, also known as ethyl alcohol or grain alcohol, can be used either as an alternative fuel or as an octane-boosting, pollution-reducing additive to gasoline. Ethanol can be produced from any biological feedstocks that contain appreciable amounts of sugar or materials that can be converted into sugar such as starch or cellulose. Sugar beets and sugar cane are examples of feedstocks that contain sugar. Corn contains starch that can relatively easily be converted into sugar. Trees and grasses are made up of cellulose and hemiceullulose, which can also be converted to sugar, although with more difficulty and expense than required to convert starch today.

The majority of ethanol production occurs utilizing corn as a feedstock by what is termed the dry grind process. This ethanol production process starts by grinding up the feedstock so it is more easily and quickly processed in the steps outlined below. Once ground up, the sugar is either dissolved out of the material or the starch or cellulose is converted into sugar. The sugar is then fed to bread yeast that use it for food, producing ethanol and carbon dioxide in the process. A final step removes the water from the ethanol.

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 sweetener.

The major steps in the dry mill process are:

Milling. The feedstock passes through a hammer mill, which grinds it into a fine powder called flour.

Fermentation. Enzymes are added to convert starch into glucose, or simple sugars. Yeast is added to the mash to convert the sugars to ethanol and carbon dioxide. The mash is continually agitated and cooled until the ethanol concentration has been maximized.

Distillation. The fermented mash, now called beer, contains about 10-18 % alcohol - plus all the non-fermentable solids from the corn and yeast cells. The mash is pumped to a distillation system where the ethanol is removed from the solids and the water. The ethanol leaves the top of the distillation system at about a 95% alcohol concentration, and the residue mash, called stillage, is transferred from the base of the column to the co-product processing area.

Dehydration. The alcohol from the top of the column passes 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. The alcohol product at this stage is called anhydrous ethanol (pure, without water) and is approximately 200 proof.

Co-Products. The stillage consists of all of the components of the original corn, sans the starch converted to ethanol.  This stillage is concentrated and dried to produce a co-product termed distillers’ dried grain with solubles – DDGS.  This product is utilized as a livestock feed. .