$ Ethanol 2000 1500 1000 50: iTFITFFiFFFFRi 9801981198219831984198519861987198819891990199119921993199419951996997199819992000200 Year Figure 1. Growth in U.S. ethanol production iF II II Abstract Last year, 1.77 billion gallons of fuel ethanol were produced in the U.S., over 90% of which was produced from corn. Ethanol demand is expect- ed to more than double in the next several years as it is used to replace the fuel oxygenate, methyl tertiary- butyl ether (MTBE). Corn is prepared for ethanol fermentation by either wet milling or dry grinding. Most newly constructed ethanol plants use dry grinding because of its lower cap- ital costs. However, corn wet millers have also expanded production by adding on to existing plants. Current technology allows for 2.5 (wet milled) to 2.7 (dry grind) gal of ethanol per bushel of corn. An opportunity exists for increasing this yield by also con- verting the fibrous components of the corn kernel (i.e. pericarp and germ) to ethanol. Fermenting these non- starch fractions could increase the yield from a bushel of corn by a max- imum of 10%. In this brief review, the economic and technical aspects of ethanol production will be explored as well as future prospects for increasing ethanol yield from corn by fermenting the non-starch fractions. Introduction The United States produced 1.77 bil- lion gal of fuel ethanol (2001) and over 90% of it was produced from corn. U.S. ethanol production has expanded dramatically since 1980 (Fig. 1) and today utilizes over 5% of the corn crop. Ethanol production should continue to increase as indi- vidual States phase out the use of methyl tertiary butyl ether (MTBE) as a fuel oxygenate. The California Energy Commission has estimated that production capacity is expected to grow to more than 4 billion gals/yr by 2006 (MacDonald et al., 2001). The growth in the use of fuel ethanol can be traced to environmen- tal legislation and Federal and State economic incentives. In 1990, the Clean Air Act amendment was passed which required the use of oxygenated fuel and reformulated gasoline to reduce carbon monoxide emissions. The list of available fuel oxygenates CO 0 X I- 0 0 0 Co 0 0) 0 w are ethanol, MTBE, and ethyl tertiary butyl ether (ETBE). Several Midwest States mandate the use of ethanol. The Federal government has also encour- aged the use of ethanol by exempting it from the federal gasoline excise tax. This tax exemption was set to expire in 2000, but has since been renewed until 2006. Several Midwestern States also introduced further financial incentives for ethanol. These incen- tives are designed to favor smaller ethanol plants, such as those built by farmer cooperatives. Typical is Minnesota's Tax incentive, which gives 20 cents per gal per year for 10 years for a maximum of 50 million gals per year. Many ethanol plants designed around this incentive have since expanded capacity. Ethanol demand is expected to increase dramatically over the next several years because of environmen- tal concerns associated with the use of MTBE. MTBE, which has leaked from gasoline storage tanks, has been dis- covered to be a major ground water contaminant and more resilient to microbial degradation than other common organic water pollutants (Anonymous, 1999). As a result of these findings, California and States located in Eastern United States have The U.S. corn ethanol industry: An overview of current technology and future prospects by Bruce S. Dien, Rodney J. Bothast, Nancy N. Nichols, and Michael A. Cotta USDA-ARS, National Center for Agricultural Utilization Research, 1815 N. University Street, Peoria, IL, USA. NT. SUGAR JNL., 2002, VOL. 104, NO. 1241