Although the positive role of non-Saccharomyces yeasts on the overall quality of wine is encouraging research into their oenological potential, current knowledge on the topic is still far from satisfactory. This work analyzes the contribution of starter cultures of Torulaspora delbrueckii, inoculated sequentially with Saccharomyces cerevisiae (multi-starter fermentation), on the fermentation and aromas of two different white style wines, i.e., dry and sweet wines. Chemical analysis of Soave and Chardonnay wines (dry wines) showed that multi-starter fermentation greatly affected the content of several important volatile compounds, including 2-phenylethanol, isoamyl acetate, fatty acid esters, C4-C10 fatty acids and vinylphenols. Moreover, strain-specific contributions have been shown by testing two different T. delbrueckii strains. Evidence of the positive impact of T. delbrueckii activity on wine quality was also demonstrated in Vino Santo, a sweet wine. Due to its low production of acetic acid, this non-Saccharomyces yeast is recommended for the fermentation of high sugar grapes. T. delbrueckii also influenced the content of different variety of chemical groups, including lactones. From a sensory perspective, all wines produced by multi-starter fermentation have greater aromatic intensity and complexity than wines resulting from a monoculture fermentation. These results emphasize the potential of employing T. delbrueckii, in association with S. cerevisiae, for the production of white wines of different styles with improved and enhanced flavour.

The impact of Torulaspora delbrueckii has been investigated for the first time in the production of Amarone wine, a high-alcohol dry red wine obtained from withered grapes. In two different vinifications, winery trials were inoculated by a selected strain of T. delbrueckii simultaneously and/or sequentially to Saccharomyces cerevisiae. Implantation analysis demonstrated T. delbrueckii was able to rapidly colonise the must remaining in wine up to 16.5 % v v -1 of ethanol. The effects of T. delbrueckii on the aroma of Amarone wine were linked to its persistence during the fermentation and a great number of compounds varied in wine obtained with mixed cultures. The most significant changes were observed among alcohols, fermentative esters, fatty acids and lactones, which are important in the Amarone wine flavour. This study confirms the role of T. delbrueckii on wine aroma and the potential of non-Saccharomyces use in winemaking.

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The purpose of this work was to study the induction of malolactic fermentation (MLF) in a wine that does not often support malic acid deacidification because of its high alcohol content. Amarone wine, known for its high alcohol content, served as a model. Simultaneous and sequential alcoholic and malolactic fermentation (AF/MLF) were conducted by direct inoculation of bacteria, which resulted in successful MLF in wines containing approximately 16% (v/v) alcohol. At higher ethanol contents, stuck MLF occurred because of growth inhibition. To overcome this technological problem, the performance of bacteria was tested in wine containing approximately 17% (v/v) ethanol using a starter preparation consisting of cells acclimatised in a wine-water solution (1:1) for 24 h and 48 h respectively. Total l-malic acid depletion was recorded when the bacterial cells that had been acclimatised for 48 h were inoculated simultaneously with yeast to conduct AF. The method by which the bacterial cultures are prepared and the time of inoculation affects the efficacy of MLF in high-alcohol wines. The inoculation of yeasts with acclimatised bacteria before AF seems to be a valid strategy to obtain complete MLF in high-alcohol wines. Malolactic fermentation (MLF) in wine is characterised by the conversion of l-malic acid to L-lactic acid and carbon dioxide, and subsequent changes in aroma and taste profiles. This secondary fermentation is usually conducted by Oenococcus oeni (Lonvaud-Funel, 1999). MLF may occur spontaneously or may be induced by the inoculation of selected bacterial cultures that are commercially available as pure freeze-dried cultures. These strains tolerate high alcohol (> 13.0%, v/v) and low pH (< 3.20), traits which allow them to grow and survive in harsh environments such as wine. These two parameters, in combination with the presence of SO 2 , low temperature and scarce nutrients, contribute to diminish the success of biological deacidification (Ribéreau-Gayon et al., 2006). The ethanol content in wine plays a critical role in MLF, as it disrupts membrane structures and affects many membrane-associated processes, including those involved in stress resistance and malolactic activity (Da Silveira et al., 2003, Chu-Ky et al., 2005).

Aims:  To explain the role of Saccharomyces cerevisiae and Saccharomyces uvarum strains (formerly Saccharomyces bayanus var. uvarum) in wine fermentation. Methods and Results:  Indigenous Saccharomyces spp. yeasts were isolated from Amarone wine (Italy) and analysed. Genotypes were correlated to phenotypes: Melibiose− and Melibiose+ strains displayed a karyotype characterized by three and two bands between 225 and 365 kb, respectively. Two strains were identified by karyotype analysis (one as S. cerevisiae and the other as S. uvarum). The technological characterization of these two strains was conducted by microvinifications of Amarone wine. Wines differed by the contents of ethanol, residual sugars, acetic acid, glycerol, total polysaccharides, ethyl acetate, 2‐phenylethanol and anthocyanins. Esterase and β‐glucosidase activities were assayed on whole cells during fermentation at 13° and 20°C. Saccharomyces uvarum displayed higher esterase activity at 13°C, while S. cerevisiae displayed higher β‐glucosidase activity at both temperatures. Conclusions:  The strains differed by important technological and qualitative traits affecting the fermentation kinetics and important aroma components of the wine. Significance and Impact of the Study:  The contribution of indigenous strains of S. cerevisiae and S. uvarum to wine fermentation was ascertained under specific winemaking conditions. The use of these strains as starters in a winemaking process could differently modulate the wine sensory characteristics.