Characterization of Indigenous Non-Saccharomyces Yeast Strains with Potential Use in Winemaking.

Background: The vineyard is a great reservoir of autochthonous yeast strains whose composition is defined by different regional (edaphology, orography or climatology) and anthropological factors (cultivation systems or cultural practices). Most of this yeast diversity corresponds to non-Saccharomyces strains, some of which have potential use in winemaking.

Methods: The oenological potential of 29 different native non-Saccharomyces strains belonging to 4 species (Lachancea thermotolerans, Torulaspora delbrueckii, Starmerella bacillaris and Metschnikowia spp.) was evaluated, using the autochthonous Saccharomyces cerevisiae XG3 strain as a control. Microfermentations with pure culture of each strain were performed in duplicate and the basic parameters and major volatiles of wines were analysed following official methodology. The best strain within each species was selected using a quantification matrix including the relevant oenological characteristics.

Results: The fermentative ability of non-Saccharomyces was lower than S. cerevisiae in all cases, but with differences among species. L. thermotolerans and T. delbrueckii showed higher fermentation rates than Starm. bacillaris, whereas Metschnikowia spp. presented a low fermentative power. At chemical level all non-Saccharomyces strains reduced the alcoholic content, the higher alcohols and the volatile acidity of wines and increased the content of glycerol, with differences among strains within a given species. T. delbrueckii and L. thermotolerans increased the total acidity of wines. The latter and Metschnikowia spp. strains produced lactic acid, which decreased the wine pH in the case of L. thermotolerans. According to their oenological traits the best rated strains of each species were Lt93, Td315, Mf278 and Sb474. In addition, the data obtained in pure fermentations were correlated to those chemical and aromatic compounds obtained with these non-Saccharomyces strains in sequential fermentations.

Conclusions: Autochthonous strains of non-Saccharomyces yeast species contribute distinctive chemical characteristics to the wines. The correlations observed between wines fermented with the different non-Saccharomyces indigenous strains in pure and sequential fermentations suggest that their contribution to wine properties remains stable regardless of must composition or winemaking techniques.