Ethanol is produced almost exclusively from corn in the USA. Corn is milled for extracting starch that is enzymatically treated for obtaining glucose syrup. Then, this syrup is fermented into ethanol. There are two types of corn milling in the industry: wet and dry. During wet milling process, corn grain is separated into its components.

Fermentation may be performed using S. cerevisiae at 30-32°C with the addition of ammonium sulfate or urea as nitrogen sources (Sanchez and Cardona, 2008). Proteases can be added to the mash to provide an additional nitrogen source (Bothast and Schlicher, 2005). Z. mobilis has also been researched for ethanol production from dry-milled corn starch (Krishnan et al., 2000). Other research efforts are oriented to the development of corn hybrids with higher extractable or fermentable starch content (Bothast and Schlicher, 2005).

Triticum spp.

Ethanol is produced from wheat (Fig. 4.10) by a process similar to that of corn. Some efforts have been done for optimising fermentation conditions (Thomas et al., 1996; Wang et al., 1999; Bayrock and Michael Ingledew, 2001; Barber et al., 2002; Soni et al., 2003). Cost is the main drawback of this alternative.

The bran fraction, which would normally be a waste product of the wheat milling industry, can be used as the sole medium to produce enzyme complexes (Dorado et al., 2009). The proposed process could be potentially integrated into a wheat milling process to upgrade the wheat flour milling by-products into platform chemicals of a sustainable chemical industry (Du, Lin, et al., 2008). If the production of co-products is optimised and residues are integrated into the process, ethanol from wheat may become a serious competitor of gasoline as a fuel.