Saccharomyces cerevisae strains

A method of preparing a strain of sugar fermenting Saccharomyces cerevisiae with capability to ferment xylose, wherein said method comprises:

• sporulating a first strain of Saccharomyces cerevisiae for providing at least 20 tetrads of said strain,
• mating the first sporulated Saccharomyces cerevisiae strain with a second Saccharomyces cerevisiae haploid strain by mixing cells of said Saccharomyces cerevisiae haploid strain with each tetrad to provide mated cells on an YPD agar plate,
• screening for the mated cells on xylose and geneticin agar plates,
• growing the mated cells in minimal defined xylose liquid media,
• verifying that the mated cells exhibit basic morphology features of budding yeast by microscopic inspection and selecting such mated cells with basic morphological features,
• creating a mixture of the mated cells with basic morphology features,
• subjecting the mixture to continuous chemostat cultivation firstly in a microaerobic environment and thereafter in an anaerobic environment using feeding strategy with defined xylose media feed at at least 0.08 h−1 in cyclus of feed and disrupted feed in a cyclus time range of a few hours, and
• obtaining the sugar fermenting Saccharomyces cerevisiae cells with capability to ferment xylose by collecting said cells from the chemostat reactor.