Sometimes technology produces unintended consequences. That appears to be the case with the ethanol by-product, distiller's grain (DG), which is fed to cattle as a corn replacement. The rub is that several studies indicate DG contains yet another by-product of the distillation process associated with ethanol production – antibiotics.

Why are antibiotics used in the distillation of ethanol? The distillation process requires a combination of enzymes and yeast to convert corn into ethanol. But bacterial organisms present during distillation can sometimes out-compete yeast in the breakdown of this sugar.

"This is what you don't want," says James Hairston, the Alabama Cooperative Extension System water quality coordinator. "The acid produced by bacteria wipes out the yeast. What you end up with is lactic acid rather than a high level of ethanol."

Instead of fuel, you end up with corn mash.

The easiest way to address this problem is to introduce antibiotics to kill the bacteria, Hairston says.

But these antibiotics not only linger following distillation, they also appear to be passed along to cattle in the DG.

Hairston says there already is a concern about the use of antibiotics in feed associated with concentrated animal feeding operations.

He and other water-resource experts fear that minute traces of antibiotics in animal waste can wash into water resources and ultimately affect the quality of drinking water and possibly even human health.

Indeed, a growing number of medical authorities fear that minute traces of antibiotics in drinking water promote the growth of antibiotic-resistant bacteria, the most serious of which are potentially deadly antibiotic-resistant bacteria known as methicillin-resistant Staphylococcus aureus (MRSA).

Water treatment facilities are currently not equipped to remove these antibiotic traces from drinking water, Hairston says.

Medical researchers are currently unsure of the extent to which these small traces of antibiotics in drinking water may contribute to the growing problem associated with antibiotic resistance.

Until now, the Food and Drug Administration (FDA) hasn’t pressed the issue of antibiotics in ethanol distillation, but this may change. Samples of DG requested from 60 ethanol plants revealed the presence of four types of antibiotics: penicillin, virginiamycin, erythromycin and tylosin.

An FDA decision to curtail antibiotic use in DG could have far-reaching effects on the ethanol industry. Currently, an estimated third of corn in distillation ends up as DG; meanwhile, DG has become a mainstay of the cattle industry.

"DG is considered a high-quality corn substitute – anybody in the livestock industry will agree," Hairston says. "And it's largely the reason why ethanol processors have managed to survive since the slump," Hairston says.

Over the next few weeks, FDA intends to inspect more samples of DG. Release of the findings is expected later this summer.

If the agency cracks down on antibiotic use, Hairston says the ethanol industry may have a tough time developing a substitute.
-- Jim Langcuster, Auburn University