Qi BioEnergy

Another potential ethanol feedstock is starch. Starch molecules are made up of long chains of glucose molecules. Thus, starchy materials can also be fermented after breaking starch molecules into simple glucose molecules. Examples of starchy materials commonly used around the world for ethanol production include cereal grains, potato, sweet potato, and cassava. Cereal grains commonly used in the US for ethanol production include maize and wheat.

Approximately 475 million tonnes of maize were produced in the world in 1990 with about 200 million t produced in the US. Approximately 8 to 9 million t, or 4% of US maize grain went into ethanol in 1990. A bushel of maize grain (25.3 kg or 56 lb. at 15% moisture) can produce from 9.4 to 10.9 L (2.5 to 2.9 gallons) of pure ethanol, depending on the technology used.

Starchy materials require a reaction of starch with water (hydrolysis) to break down the starch into fermentable sugars (saccharification). Typically, hydrolysis is performed by mixing the starch with water to form a slurry which is then stirred and heated to rupture the cell walls. Specific enzymes that will break the chemical bonds are added at various times during the heating cycle.