Microbiological contamination is a major problem for commercial fuel ethanol production in distilleries all over the world. Undesirable microorganisms compete with yeasts for nutritional substances; moreover, they produce lactic and acetic acids that harm yeast cells. One of the sources of microbiological pollution in the fermentation process is raw materials (e.g. grains). It is important to find out what kind of microflora contaminate them, and new technologies should be developed to reduce this contamination. The aim of this work was to determine the total number of mesophilic bacteria, the number of lactic acid bacteria, anaerobic bacteria, moulds, and yeasts that occur in raw materials used in distilleries in Poland’s Wielkopolska region. Moreover, the numbers of these microorganisms in the sweet mash, in the sweet mash after 24 hours of fermentation, and after complete fermentation were counted. We decided to check out the microbiological state of raw materials and fermentation mashes because of the low bioethanol efficiency reached in these small ethanol plants. In all five distilleries, mesophilic bacteria, lactic acid bacteria, anaerobic bacteria, moulds, and yeasts occurred in grains. The level of contamination was relatively high. These groups of microorganisms were also present in the sweet mash, in the sweet mash after 24 hours of fermentation and after complete fermentation. The level of contamination was similar in all distilleries that use the same raw materials, and it was rather high. So the obtained results (relatively high raw material and fermentation mashe microbiological contamination) can explain the low ethanol efficiency found in all tested distilleries.
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