Selection of a robust yeast strain tailored for ethanol production

Ethanol production in Brazil is based on fast fermentations (6-12hours) and high concentrations of yeast (8-15% w/v) in large volume tanks (250,000 to 3,000,000 liters). However, this process is subject to contamination by wild Saccharomyces that may cause serious problems such as, low fermentation yield, flocculation and residual sugars in the wine. Our objective was to select a new strain, more adapted to fermentation process of Alta Mogiana sugarcane mill (160 million liters ethanol/year). We considered that the best way to discover a robust yeast would be the natural selection of dominant and persistent strains in industrial fermentations. The main steps were: 1) monitoring the population of dominant and persistent strains by karyotyping and mitochondrial DNA, 2) evaluation of strains in small-scale, 3) re-introduction of the best strain in industrial fermentation process and 4) evaluation of the industrial performance. The results allowed the selection of a very robust strain (UAM) increasing the alcoholic content in wine (from 8 to 10%) and the industrial efficiency of sugar recovery (from 88.8 to 92.4%), saving thermal energy and bagasse (10,000 tons), reducing vinasse volumes (1.2 liter less vinasse per liter of ethanol) and lowering the risk of contamination by wild Saccharomyces. These results demonstrate the feasibility in the near future each plant will have its own customized yeast.

ACKNOWLEGMENTS: CAPES, CNPq, FAPESP and Usina Alta Mogiana S/A