Use of selected indigenous yeasts from racemes of Grillo grape variety to improve the production of sparkling base wine

Abstract

The production of sparkling wines in Sicily is increasing considerably. The most important oenological characteristics of high quality sparkling wines are high content of acidity and low pH. In Sicily, white grape varieties such as those of the cultivar Grillo are characterized by very low concentrations of malic and tartaric acids due to hot climate and reduced rainfall typical of the production area. On the other hand, a very large amount of raceme grapes, characterized by low pH and high content of tartaric and malic acids, is largely produced by Grillo varieties. Hence, the winemaking of racemes might represent a technological solution to increase the quality of the acids in the final wines. At the same time, the selection of yeast strains able to ferment grape must at very low pH is mandatory. With this in mind, the present research was carried out to isolate and selected novel yeast strains from racemes of Grillo cultivar and to set up an innovative ad hoc winemaking protocol to increase the acidity of sparkling base wine. From spontaneous vinifications on Grillo grape racemes, 2873 yeasts were isolated and characterized at the phenotypic and genotypic level. A total of 493 Saccharomyces cerevisiae isolates were subject to intraspecific characterization by interdelta analysis. These strains were also screened on the basis of technological criteria (fermenting power and vigor, SO2 and alcohol tolerance and flocculence) and qualitative features (H2S production). Four strains of S. cerevisiae were selected and inoculated individually into must obtained from Grillo racemes at 12 and 16 % (w/v) of total sugars. All strains displayed a technological potential to drive the fermentation of must into wine at very low pH (2.5-2.8). The inoculation of the strains was performed after a pre-adaptation at pH 2.5. Thus, starters were able to successfully lead fermentation. For the first time an ecological investigation of yeast ecology of raceme grapes has been carried out and an innovative strategy to improve acidity of sparkling base wine in hot climate regions has been designed.