Characterization of Yeasts Involved in the Biological Ageing of Sherry Wines

Yeast strains that form flor velum during the ageing process of sherry have been isolated and characterized. According to their metabolic features, the racesbeticusandcheresiensisofSaccharomyces cerevisiaewere the main components of the flor velum, although minority yeasts belonging to eitherSaccharomycesorPichiawere also identified. Yeasts were also studied at molecular level, by pulsed field gel electrophoresis, and analysis of variability of mtDNA. Considerable polymorphism was detected by the analysis of the karyotypes, and although most of the patterns were common to both races a specific pattern ofcheresiensisdid appear. Analysis of mtDNA restriction also yielded a high genetic variability; most of the patterns were common to the two races but a unique pattern ofcheresiensiswas also detected. Molecular data were compared and a preferential association between karyotype and mtDNA patterns was shown. A correlation between different blending stages and both chromosomal and mtDNA restriction profiles was found, so that molecular patterns, rather than metabolic races, were associated to specific stages of the biological ageing process. Such a finding has major significance for the improvement of sherry.