Ethanol is produced by fermentation, a sequence of reactions which release energy from organic molecules in the absence of oxygen i.e. energy is obtained when sugar is changed to ethanol and carbon dioxide. All beverage ethanol and more than half of industrial ethanol is made by this process.

   Traditional fermentation processes rely on yeasts to convert six-carbon sugars to ethanol. Glucose, the preferred form of sugar for fermentation, is contained in both carbohydrates and cellulose. Since carbohydrates are easier than cellulose to convert to glucose, the majority of ethanol currently produced in the United States is made from corn.

   Before fermentation can occur, starch in corn must be broken down into simple sugars by cooking the corn and adding the enzymes alpha amylase and gluco amylase. These enzymes function as catalysts to speed up the chemical changes from starch to a simple sugar.

   Then yeast, a single-celled fungi which feeds on the sugar and produces alcohol (ethanol) and carbon dioxide(a process called fermentation), is added. During fermentation, the ethanol retains much of the energy that was originally in the sugar, making ethanol is an excellent fuel.

The fermentation reaction is represented by the following equation: