Volatile composition of partially fermented wines elaborated from sun dried Pedro Ximénez grapes.

In this work, we used a cell immobilisation system consisting of Penicillium chrysogenum fungi (GRAS) bound to the osmotolerant yeast strains Saccharomyces cerevisiae X4 and X5 for the partial fermentation of raisin musts. The resulting wines were compared with others obtained by partial fermentation of musts with free yeasts and with a traditionally produced sweet wine (i.e. without fermentation of the must). The analysis of volatile compounds grouped by aroma series showed the partially fermented musts had a more complex aroma than the traditional wine. Specially prominent among aroma series was that of ripe fruit, followed by the milky and chemical series. The volatiles with the greatest impact on wine aroma as assessed in terms of odour activity were ethyl hexanoate, ethyl octanoate, butyrolactone, isoamyl alcohols, acetaldehyde, ethyl acetate, 2,3-butanediol, acetoin and 2,3-butanedione. A cluster analysis according to the Ward method was performed to assess the similarity between the traditional sweet wine and those obtained by partial fermentation with free and immobilised yeasts revealed small differences between the wines obtained with free and immobilised yeasts, and marked differences between partially fermented and traditionally obtained sweet wine. The wines provided by immobilised yeasts were the most appreciated in the sensory analysis (especially those obtained with X4 yeasts).

Use of two osmoethanol tolerant yeast strain to ferment must from Tempranillo dried grapes: effect on wine composition.

The must from Tempranillo dried grapes was divided into four batches to produce sweet wine. The first one was fortified with ethanol up to 12% (v/v) to avoid fermentation (traditional way). Other two batches were partially fermented with two osmoethanol tolerant Saccharomyces cerevisiae strains (X4 and X5). The last one was fermented with native yeast by spontaneous fermentation. Wines fermented partially with the strains X4 and X5 show high volatile acidity values (above 2g/L expressed as acetic acid), and a glycerol concentration around 20 g/L. Both strains also produce high amount of carboxylic acids and therefore the wines show a high ethyl ester concentration. Aromatic series were obtained for all the wines by grouping aroma compounds according to their odor descriptors. The series of the fermented wines with higher values in relation with the control wine were fruity, sweet and fatty, emphasizing the fruity series in the samples fermented with the X4 and X5 strains. The sensorial analysis of the wine samples by a tasting panel put in evidence that the musts fermented with the osmoethanol tolerant yeasts were better valued than the rest of the wine samples. The must fermented with the X4 strain obtained the maximum score in terms of aroma and flavour. So, the use of these osmoethanol tolerant S. cerevisiae strains could be a suitable alternative to produce sweet wines from must with high sugar concentration. The wines obtained this way are chemically and organoleptically more complex than those elaborated traditionally.

Effect of a short contact time with lees on volatile composition of Airen and Macabeo wines.

Volatile compounds were analyzed in Airen and Macabeo wines at the end of the alcoholic fermentation and after a short time contact with wine lees. The concentration of 34 analyzed compounds, with the exception of hexyl acetate, linalool, ss-ionone and farnesol, increased significantly after contact with lees in Airen wines. Esters and terpenic compounds decreased significantly in Macabeo wines after contact with lees. The contact with lees could be considered as favourable in Airen wines to improve the aroma quality.

Relationship between ethanol tolerance, H+ -ATPase activity and the lipid composition of the plasma membrane in different wine yeast strains.

Ethanol tolerance, ATPase activity and the lipid composition of the plasma membrane to study potential relationship among them were examined in five different wine yeast strains. Yeast cells were subjected to ethanol stress (4% v/v). Principal component analysis of the results revealed that the wine yeasts studied can be distinguished in terms of ATPase activity and oleic acid (C18:1), and palmitoleic acid (C16:1), in plasma membrane. Multiple regression analysis was used to identify a potential influence of some components of the plasma membrane on ethanol tolerance and ATPase activity. Based on the results, the ergosterol, oleic acid and palmitoleic acid are highly correlated with ATPase activity and ethanol tolerance. Ethanol tolerance and the ATPase activity of the plasma membrane were correlated at the 96.64% level with the oleic acid and ergosterol in plasma membrane. The Saccharomyces cerevisiae var. capensis flor yeast strain, which exhibited the highest ergosterol concentration in plasma membrane when grown in the presence of 4% v/v ethanol, was found to be the most ethanol-tolerant.

Changes in volatile compounds and aromatic series in sherry wine with high gluconic acid levels subjected to aging by submerged flor yeast cultures.

Volatile compounds of sherry wine containing gluconic acid under aging by submerged flor yeast cultures were analyzed. The aroma profile was obtained by grouping the compounds in nine aromatic series. The balsamic, fatty, herbaceous and empyreumatic series increased significantly as consequence of the increase of pantolactone, acids (butanoic, 2-methylbutanoic and 3-methylbutanoic), methionol and gamma-butyrolactone compounds, respectively. The decrease of higher alcohols promoted solvent series diminished. These changes are consistent with those observed in the production of commercial sherry wine using traditional biological aging.

Changes in gluconic acid, polyols and major volatile compounds in sherry wine during aging with submerged flor yeast cultures.

The traditional biological process by which sherry wines are aged can be accelerated by using submerged Saccharomyces cerevisiae var. capensis (G1) strain cultures previously grown in glycerol. The used controlled shaking conditions raise the acetaldehyde, acetoin, and meso 2,3-butanediol contents in the wine, and increases the consumption of gluconic acid by flor yeast relative to traditional biological aging under flor yeast velum.