Fermentation processes produce a wide range of chemicals that complement the various chemicals produced by nonfermentation routes. For example, alcohol, acetone, butyl alcohol, and acetic acid are produced by fermentation as well as by synthetic routes. Almost all the major antibiotics are obtained from fermentation processes.
Fermentation under controlled conditions involves chemical conversions, and some of the more important processes are:
1. Oxidation, e.g., ethyl alcohol to acetic acid, sucrose to citric acid, and dextrose to gluconic acid
2. Reduction, e.g., aldehydes to alcohols (acetaldehyde to ethyl alcohol) and sulfur to hydrogen sulfide
3. Hydrolysis, e.g., starch to glucose and sucrose to glucose and fructose and on to alcohol
4. Esterification, e.g., hexose phosphate from hexose and phosphoric acid