Yeast population dynamics during the fermentation and biological aging of sherry wines.

Molecular and physiological analyses were used to study the evolution of the yeast population, from alcoholic fermentation to biological aging in the process of "fino" sherry wine making. The four races of "flor" Saccharomyces cerevisiae (beticus, cheresiensis, montuliensis, and rouxii) exhibited identical restriction patterns for the region spanning the internal transcribed spacers 1 and 2 (ITS-1 and ITS-2) and the 5.8S rRNA gene, but this pattern was different, from those exhibited by non-flor S. cerevisiae strains. This flor-specific pattern was detected only after wines were fortified, never during alcoholic fermentation, and all the strains isolated from the velum exhibited the typical flor yeast pattern. By restriction fragment length polymorphism of mitochondrial DNA and karyotyping, we showed that (i) the native strain is better adapted to fermentation conditions than commercial strains; (ii) two different populations of S. cerevisiae strains are involved in the process of elaboration, of fino sherry wine, one of which is responsible for must fermentation and the other, for wine aging; and (iii) one strain was dominant in the flor population integrating the velum from sherry wines produced in González Byass wineries, although other authors have described a succession of races of flor S. cerevisiae during wine aging. Analyzing all these results together, we conclude that yeast population dynamics during biological aging is a complex phenomenon and differences between yeast populations from different wineries can be observed.

[Sherry wine microorganisms]. / Los microorganismos del jerez.

Sherry wine presents, during all its wine-making and aging process, a great diversity of yeast and bacteria, as well as in the wine itself; its particular wine-making system, with traditional and legal additions to correct the acidity and to get a final alcoholic content of 15%, originates a selection of accompanying microorganisms. Species of the genera Kloeckera, Candida, Saccharomyces, Pichia, Hansenula and Saccharomycodes, have been isolated during the fermentation process in different proportions. This fact confirms that, besides S. cerevisiae, strains of S. chevalieri and S. fermentati have an important role in the fermentative process, and that the film-forming Saccharomyces have great activity in the fermentation. The biological aging of the Sherry wine, carried out by S. cheresiensis, S. beticus, S. feduchii and S. rouxii, has been studied in "finos" and "manzanillas". Different species and percentages in both wines have been described.