Fermentation, one of the oldest chemical processes known to humans and most widely practiced by them, is used to produce a variety of useful prod­ucts and chemicals. In recent years, however, many of the products that can be made by fermentation are also synthesized from petroleum feedstock, often at lower cost or more selectively. It is also true that modern efforts of exploiting renewable biological resources rather than nonrenewable petro­leum resources as well as focusing on green technologies, thereby allevi­ating the process involvement of harmful chemicals, are strong drivers for biological treatment processes such as fermentation. The future of the fer­mentation industry, therefore, depends on its ability to utilize the high effi­ciency and specificity of enzymatic catalysis to synthesize complex products and also on its ability to overcome variations in the quality and availability of the raw materials.

Ethanol can be quite easily derived by fermentation processes from any material that contains sugar(s) or sugar precursors. The raw materials used in the manufacture of ethanol via fermentation are classified as sugars, starches, and cellulosic materials [15, 16]. Sugars can be directly converted to ethanol by simple chemistry, as fully discussed in Chapter 3. Starches must first be hydrolyzed to fermentable sugars by the action of enzymes. Likewise, cellulose must first be converted to sugars, generally by the action of mineral acids (i. e., inorganic acids such as the common acids sulfuric acid, hydro­chloric acid, and nitric acid). Once the simple sugars are formed, enzymes from yeasts can readily ferment them to ethanol.