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Biofuels explained Ethanol

Ethanol is made from biomass

Fuel ethanol is anhydrous, denatured alcohol that meets the American Society of Testing and Materials (ASTM) standard specification D4806 for ethanol use in spark-ignition engines. Most of the fuel ethanol produced around the world is made by fermenting the sugar in the starches of grains such as corn, sorghum, and barley, and the sugar in sugar cane and sugar beets. Denaturants are added to ethanol to make fuel ethanol undrinkable. In the United States, nearly all fuel ethanol is produced from corn kernel starch, which is considered a conventional biofuel under the U.S. Renewable Fuel Standard Program (RFS).

Ethanol has other potential sources aside from fermentating grain starch and sugars. Researchers have experimented with several feedstocks, including:

  • Agriculture residues such as corn and rice stalks
  • Fast-growing poplar and willow trees
  • Grasses like switchgrass, which can produce two harvests a year for many years without annual replanting
  • Biomass in municipal solid waste

Trees and grasses require less fuel, fertilizers, and water to grow than grains do, and they can grow on lands that are not suitable for growing food crops. Ethanol made from these sources is called cellulosic ethanol and is considered an advanced biofuel under the RFS. However, despite the technical potential for cellulosic ethanol production from those sources, production is not economically advantageous for producers. As of the end of 2022, the United States had no commercial cellulosic ethanol production. Brazil—the world's second-largest consumer of fuel ethanol after United States—uses sugar cane to produce ethanol, which qualifies as an advanced biofuel in the United States under the RFS.

A photograph of microbiologist Nancy Nichols and biochemical engineer Bruce Dien adding yeast to a bioreactor to begin ethanol fermentation. Photo by Scott Bauer.

USDA researchers adding yeast to begin ethanol fermentation

Photo Credit: Scott Bauer, USDA Agricultural Research Service (public domain)

Ethanol is blended with gasoline

Nearly all motor gasoline now sold in the United States is about 10% ethanol by volume. Motor gasoline with 10% ethanol content by volume is called E10. Any gasoline-powered vehicle in the United States can use E10. Cars, light trucks, and medium-duty vehicles starting with model year 2001 can use E15. Only flexible-fuel vehicles can use gasoline with a higher ethanol content than 15%. E85, a fuel that contains 51%–83% ethanol, depending on location and season, is mainly sold in the Midwest and can only be used in a flexible-fuel vehicle.

Gasoline that does not contain ethanol—E0 (or ethanol-free gasoline)—may be available in some locations around the country for gasoline-powered tools, landscaping equipment, boats, and other equipment with gasoline engines for which E0 is recommended.

Last updated: February 23, 2024.