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How is Ethanol Produced?

Ethanol Production Process - Dry Milling

In dry milling, the entire corn kernel is first processed into flour, which is referred to in the industry as "meal." This meal is then slurried with water to form a "mash." Enzymes are added to the mash to convert the starch to dextrose, a simple sugar. Ammonia is added for pH control and as a nutrient to the yeast.

The mash is processed in a high-temperature cooker at approximately 105 degrees Celsius to reduce bacteria levels ahead of fermentation. The mash is cooled to around 35 degrees Celsius and transferred to fermenters where yeast is added and the transformation of sugar to ethanol and carbon dioxide (CO2) begins.

The fermentation process takes approximately 40 to 60 hours. At this point of the process, the mash is agitated and kept cool to facilitate the activity of the yeast. After fermentation is completed, the resulting "beer" is transferred to distillation columns where the ethanol is separated from the remaining "stillage." The ethanol is concentrated to 190 proof using conventional distillation and then is further dehydrated to approximately 200 proof. Often this is done in a molecular sieve system.

The anhydrous (pure) ethanol is then blended with about 2-5% denaturant (such as natural gasoline) to render it undrinkable so that it is not subject to beverage alcohol tax. The finished product can then be shipped to gasoline terminals or retailers.

Co-Products: DDGS, Corn Oil & CO2

The stillage is sent through a centrifuge that separates the coarse grain from the solubles. The solubles are then concentrated to about 30% solids by evaporation, resulting in Condensed Distillers Solubles (CDS) or "syrup." Syrup is sent through a centrifuge to remove corn oil. Corn oil is used for livestock feed or biodiesel production. The coarse grain and the remaining syrup are then dried together to produce dried distillers grains with solubles (DDGS), a high quality livestock feed. The CO2 released during fermentation can be captured and sold for use in carbonating soft drinks and beverages and the manufacture of dry ice.

For more information the ethanol production process, please visit the Renewable Fuels Association website at or the American Coalition for Ethanol website at

What are the benefits of using ethanol?

  • Improved Air Quality: Ethanol increases the oxygen content of fuel, leading to more complete combustion, reduced tailpipe emissions and reduced greenhouse gas emissions.

  • Cleaner Power: Ethanol increases the octane rating of fuel-providing enhanced performance while reducing the level of toxins in gasoline.

  • Reduced Reliance on Imported Oil: Ethanol is made from renewable sources produced in the U.S., thus extending our nation’s fuel supply.

  • Environmentally Friendly: In addition to its clean air benefits, ethanol does not pollute groundwater.

  • Sources: Renewable Fuels Association, American Coalition for Ethanol