The odor activity values (OAVs) for 49 aroma compounds in commercial sherry pale white wines were grouped, according to the similarity of their aroma descriptors, into nine odor classes with a view to establishing the aroma profile for this type of wine. The results revealed the profile to be largely comprised of the series named "fruity" and "balsamic", mainly as a result of the 1,1-diethoxyethane content in the wines. The same series were calculated from the OAVs obtained in biological aging experiments, carried out with selected strains of the flor yeasts Saccharomyces cerevisiae and Saccharomyces bayanus, over a period of 9 months. Based on the aroma profiles thus obtained, after 6 months of aging the latter race yielded OAVs for the fruity and balsamic series not significantly different (p < 0.05) from those for commercial wines aged for 5 years. However, except for the series named "solvent", all others exhibited lower values in the experiments carried out with selected strains than in the commercial wines, mainly as a result of the absence of contact with wood of the former wines. Taking into account the results, the biological aging of this type of sherry wine can be shortened by subjecting it to controlled aging with selected yeast strains in a first stage and subsequently allowing it to stand in wood casks in a second stage.

Changes in 36 volatile compounds of must from ripe grapes dried by direct exposure to sun and must from ripe grapes were studied. Compounds not dependent on sampling site in both musts were selected, and their concentration/Brix degree ratio values, were subjected to variance analysis. Only butan-1-ol and isoamyl alcohols showed no differences, while (E)-hex-3-en-1-ol, (Z)-hex-3-en-1-ol, (E)-hex-2-en-1-ol, (E)-hex-2-enal, hexanoic acid, isobutanol, benzyl alcohol, 2-phenylethanol, gamma-butyrolactone, gamma-hexalactone, and 5-methylfurfural, showed significant differences between the two must types, which may be ascribed to the drying process. An approach to describe must odor has been carried out by grouping volatile compounds in aromatic series, increasing their values in the fruity, solvent, sweet, and roasted series and diminishing the herbaceous as a consequence of the drying process.

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Two flor yeast strains of Saccharomyces cerevisiae (S. cerevisiae strains capensis and bayanus) which form velum on the surface of sherry wine during biological aging have been used. Aldehyde and alcohol (isoenzymes I and II) dehydrogenases were detected in vitro during the entire wine-aging process in the flor yeast strains. All enzymatic activities decreased during the first 155 days of wine aging, and after this period, an increase was observed. Ethanol consumption in the wine and the specific activity of alcohol dehydrogenase I were independent of the S. cerevisiae strain. The greater activity of alcohol dehydrogenase II is directly related to the higher acetaldehyde production by S. cerevisiae race bayanus in the wine. This strain has a slower and prolonged growth in the flor film, which permits a continued accumulation of acetaldehyde in the wine. The higher activity of aldehyde dehydrogenase in capensis strain during the flor formation may be related to the production and consumption of large amounts of acetic acid, which involved a more abundant and accelerated cellular growth. We suggest that part of the acetaldehyde might be converted into ethanol during wine aging by alcohol dehydrogenase I in order to maintain a normal redox balance. Keywords: Flor yeast; alcohol dehydrogenase; aldehyde dehydrogenase; biological aging; sherry wine

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