Potentialities and limitations of direct alcoholic fermentation of starchy material with amylolytic yeasts

Summary The fermentation characteristics of a large number of starch-degrading yeasts were compared. None of the amylolytic yeasts currently recognized, appear to be entirely suitable for direct alcoholic fermentation of starchy biomass. The species capable of extensive starch hydrolysis produce only low amounts of ethanol from glucose and dextrin, one of the major limitations being their low ethanol tolerances. Some of the less-active yeasts have much better glucosefermentation characteristics, but dextrin conversion is limited probably due to the nature of their enzyme systems. Using an -amylase dextrin (22.5% w/v), ethanol yields of about 70% were obtained with Saccharomyces diastaticus strains. Through associative fermentation of S. diastaticus and other selected amylolytic yeasts slightly better yields, however not exceeding 80%, were obtained.