Bacterial contaminants of fuel ethanol production

  • Kelly A. Skinner
  • Timothy D. Leathers
Original Paper


Bacterial contamination is an ongoing problem for commercial fuel ethanol production facilities. Both chronic and acute infections are of concern, due to the fact that bacteria compete with the ethanol-producing yeast for sugar substrates and micronutrients. Lactic acid levels often rise during bouts of contamination, suggesting that the most common contaminants are lactic acid bacteria. However, quantitative surveys of commercial corn-based fuel ethanol facilities are lacking. For this study, samples were collected from one wet mill and two dry grind fuel ethanol facilities over a 9 month period at strategic time points and locations along the production lines, and bacterial contaminants were isolated and identified. Contamination in the wet mill facility consistently reached 106 bacteria/ml. Titers from dry grind facilities were more variable but often reached 108/ml. Antibiotics were not used in the wet mill operation. One dry grind facility added antibiotic to the yeast propagation tank only, while the second facility dosed the fermentation with antibiotic every 4 h. Neither dosing procedure appeared to reliably reduce overall contamination, although the second facility showed less diversity among contaminants. Lactobacillus species were the most abundant isolates from all three plants, averaging 51, 38, and 77% of total isolates from the wet mill and the first and second dry grind facilities, respectively. Although populations varied over time, individual facilities tended to exhibit characteristic bacterial profiles, suggesting the occurrence of persistent endemic infections.


Bacterial contamination Dry grind Fuel ethanol Lactobacillus Wet mill 



The authors thank the fuel ethanol companies that participated in this study, who requested that their contributions remain anonymous. Expert technical assistance was provided by Melinda S. Nunnally.


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Copyright information

© Society for Industrial Microbiology 2004

Authors and Affiliations

  1. 1.Fermentation Biotechnology Research Unit National Center for Agricultural Utilization Research, USDA, Agricultural Research ServicePeoriaUSA

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