A letter from George R. Lester cites "well-reviewed studies" by David Pimentel and by Ted Patzak that show a negative energy balance in the corn-to-ethanol process (C&EN, Oct. 23, 2006, page 4).
Two more recent publications are worth mentioning. The first, by Alexander Farrell et al., analyzed six "high-profile studies," including those by Pimentel and Patzak, for "errors, inconsistencies, and outdated information" (Science 2006, 311, 506). The corrected data led to the same conclusion that "making ethanol from corn uses less petroleum than making gasoline."
The second paper, by Jason Hill et al., analyzed energy balances, including studies of environmental, soil, and land-use issues (Proc. Natl. Acad. Sci. USA 2006, 103, 11206). It is the 25% energy gain from corn to ethanol cited in this paper that Lester warns us about. To the authors, even this positive balance is moot, since ultimately, cellulose from energy crops such as switch grass, not cornstarch, will serve as the raw material for ethanol-producing biorefineries. Energy balance and environmental impact are much more favorable with cellulose from energy crops grown specifically for this purpose.
Finally, I find Lester's broad-brush dismissal of calculations from the Department of Energy and the Department of Agriculture lacking in careful discrimination. We do need to evaluate sources of information for possible built-in bias, but we must do the hard work to separate the good from the bad.
Gerald J. Mantell