The present application relates to improved Saccharomyces cerevisiae yeast strains that co-express a gene encoding a glucoamylase of fungal origin and a gene encoding the glucoamylase of Saccharomyces cerevisiae var. diastaticus. The present invention also relates to a method for obtaining these yeast strains involving a) genetically modifying a Saccharomyces cerevisiae yeast to co-express a gene encoding a glucoamylase of fungal origin and a gene encoding the glucoamylase of Saccharomyces cerevisiae var. diastaticus; b) culturing and fermenting the strain obtained in step a) on a dextrin medium; c) selecting the strains having fermentation kinetics at least equal to or greater than those obtained with the strain deposited at the CNCM [French National Collection of Microorganism Cultures] under number I 4999 under the same conditions. The yeast strains according to the invention are of particular interest in producing bioethanol.