The ethanol production process starts by grinding up the feedstock so it is more easily and quickly processed. Once it is ground, the sugar is either dissolved out of the material or the starch or cellulose is converted into sugar. The sugar is then fed to microbes that use it for food, producing ethanol and carbon dioxide in the process. A final step purifies the ethanol to the desired concentration. Ethanol also can be made from a wet-milling process. Many larger ethanol producers use this process, which also yields products such as high-fructose corn sweetener.
Below is a diagram of the process.