The ethanol process



Bio-ethanol can be produced from various sugar-rich substrates: globally, sugar-cane, sugar-beet, corn (Zea mays) and wheat are most commonly used. In Sweden, bio-ethanol is mainly produced from wheat. The production of ethanol from sugar is a fermentation process that occurs at low oxygen concentration and the most common microorganism in commercial use is the yeast, Saccharomyces cerevisiae. Different types of fermentation strategies are applied: batch or continuous. Certain continuous processes also include recycling of the yeasts, in order to suppress the tendency to build-up biomass and to direct the substrate utilisation towards ethanol production.  


Different fermentation regimes require different capabilities of the yeast strains involved; thus, particular regimes may select for genetic variants of the fermentation yeast. However, it is almost a dogma that those variants still belong to the species Saccharomyces cerevisiae, which is regarded as the best fermentation yeast. Unexpectedly, we found another species, Dekkera bruxellensis, together with a lactic acid bacterium dominating a commercial fermentation process (use of the consortium for ethanol production is patent pending). The role of lactic acid bacteria in ethanol fermentation has not been well characterised. They are typically regarded as contaminants, but may also play a positive role by inhibiting other contaminating organisms.



Main issues to be investigated in this project are:


  1. The role of lactic acid bacteria during bio-ethanol production
  2. Fermentation characteristics of D. bruxellenis, as compared to S. cerevisiae.