Perhaps the most persistent debate around corn ethanol involves its “net energy balance” — that is, whether it consumes more energy in production than it delivers as a fuel. Even the studies that credit the fuel with a robust energy balance, like this one from the USDA, acknowledge that it’s pretty much a wash unless you account for the "co-product" of the ethanol-making process.

The ethanol process consumes only the starch component of corn, leaving behind nearly a third of the input corn as a high-protein, high-fat substance called "distillers grains." According to ethanol boosters, this stuff makes a high-quality feed for confined animals. And indeed, as ethanol production has surged along with corn prices over the last year, CAFO operators are turning more and more to ethanol waste as feed, mainly for cows, but for poultry and hogs as well.

I’ve often wondered this: If whole corn is bad for cows — evidently corn-heavy diets ruin cows’ livers — might fragmented corn that’s been through an industrial process be even worse? Turns out the answer may be "yes."

Remember E. coli 0157, the deadly strain that poisoned several people last year who had been exposed to it through tainted spinach? Barely a week goes by these days without a massive recall of ground beef tainted with 0157. According to a new study by Kansas State University researchers, cows whose rations include distillers grains harbor E. coli 0157 at about twice the rate of cows who don’t.

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Update [2007-12-4 16:36:43 by Tom Philpott]:USA Today just came out with a startling article on recalls of E. coli-tainted meat. There have already been 54 recalls this year (one a week!), vs. 34 in 2006. And in those recalls, the USDA only managed to recover 44 percent of the tainted meat. Worse, of the five recalls that involved consumers getting sick, the agency got back just 20 percent of the meat. Hat tip to Bonnie of Ethicurean.

Correction: The USA Today piece refers to recalls of meat generally, not just for beef infected with E. coli 0157. There have been 20 E. coli 0157 cases this year, a significant rise over recent years.

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Okay, back to distillers grains. The researchers haven’t figured out why distillers grains boost E. coli 0157 rates. As the press release puts it, it might be "something that changes in the animals’ hindgut as a result of feeding distiller’s grains, or maybe the byproduct provides a nutrient for the bacteria."

Recall that E. coli 0157 itself is a new phenomenon; it was virtually unknown before the 1970s, when livestock producers moved cows from a primarily grass-based diet to a corn-dominated one.

Evidently, corn-heavy diets change the pH of cows’ guts, resulting in a much more acidic intestinal environment. This effect not only destroys cows’ livers, but also allows ever more virulent strains of E. coli, such as 0157, to thrive.

For boosters of corn-based ethanol as a "green fuel," the whole co-product issue must be a troublesome one. The fuel’s only claim to a positive energy balance rests on use of distillers grains — and the only use we’ve found for it is for feedlot meat production: surely one of the ungreenest industries known to man.