The yeast and lactic acid bacteria populations in an industrial ethanol fermentation process were investigated using PCR-fingerprinting and rDNA sequencing. This process had originally been inoculated with Saccharomyces cerevisiae. However, in the stably running process, the dominating yeast was instead Dekkera bruxellensis, together with a high number of lactic acid bacteria, almost exclusively Lactobacillus vini. D. bruxellensis is a common contaminant in the wine industry, but is also a production organism in the brewing of Lambic beer and in the generation of sour dough. Although lactic acid bacteria usually are unwanted in ethanol fermentations, they did not seem to affect the process in a negative way. Accordingly, the number of yeast cells was highest when the number of lactic acid bacteria was highest, only low levels of non-desired side-products were detected and the ethanol productivity was in the normal range. D. bruxellensis, together with L. vini, can thus be regarded as ethanol production organisms (patent pending).