There are two main types of corn ethanol production: dry milling and wet milling. In the dry milling process the corn kernel is ground into flour (known as “meal”). Water is then added to make a “mash”. Then enzymes are added to convert this starch to dextrose. Ammonia is then added to control the pH and to serve as a nutrient for the yeast to be added later. The mixture is processed at high-temperatures to reduce bacteria levels and transferred and cooled in fermenters. Yeast is then added and conversion from sugar to ethanol and carbon dioxide begins.
In a wet milling process, the corn grain is steeped in a diluted combination of sulfuric acid and water for one to two days to separate the grain into many components. The slurry mixture then goes through a series of grinders that separate the corn germ out. The corn oil by-product of this process is extracted and sold (or more recently used as a new revenue stream as a feedstock for biodiesel). The remaining components – fiber, gluten and starch are segregated out. The gluten protein is dried and filtered to make a corn gluten- meals co-product and is highly sought after by poultry broiler operators as a feed ingredient. The steeping liquor produced is concentrated and dried with the fiber and sold as corn gluten feed to in the livestock industry. The heavy steep water is also sold as a feed ingredient and is used as an alternative to salt in the winter months. The corn starch and remaining water can then be fermented into ethanol, dried and sold, or made into corn syrup.
The use of ethanol is widespread. Almost all gasoline in the U.S. contains a low-level blend E10 (10% ethanol, 90% gasoline) of ethanol. It is also widely available in higher level blends such as E-85 for use in flexible fuel vehicles.
Ethanol provides significant economic, environmental and security benefits and is gaining greater market share worldwide.