Differential malic acid degradation by selected strains of Saccharomyces during alcoholic fermentation.

To produce a high-quality wine, it is important to obtain a fine balance between the various chemical constituents, especially between the sugar and acid content. The latter is more difficult to achieve in wines that have high acidity due to excess malic acid, since wine yeast in general cannot effectively degrade malic acid during alcoholic fermentation. An indigenous Saccharomyces paradoxus strain RO88 was able to degrade 38% of the malic acid in Chardonnay must and produced a wine of good quality. In comparison, Schizosaccharomyces pombe strain F effectively removed 90% of the malic acid, but did not produce a good-quality wine. Although commercially promoted as a malic-acid-degrading wine yeast strain, only 18% of the malic acid was degraded by Saccharomyces cerevisiae Lalvin strain 71B. Preliminary studies on the transcriptional regulation of the malic enzyme gene from three Saccharomyces strains, i.e. S. paradoxus RO88, S. cerevisiae 71B and Saccharomyces bayanus EC1118, were undertaken to elucidate the differences in their ability to degrade malic acid. Expression of the malic enzyme gene from S. paradoxus RO88 and S. cerevisiae 71B increased towards the end of fermentation once glucose was depleted, whereas no increase in transcription was observed for S. bayanus EC1118 which was also unable to effectively degrade malic acid.