Yeast and its importance to wine aroma – a review

Abstract

The most mysterious aspect of wine is the endless variety of flavours that stem from a complex, completely non-linear system of interactions among many hundreds of compounds. In its widest sense, wine flavour refers to the overall impression of both aroma and taste components. Aroma is usually associated with odorous, volatile compounds, while the bouquet of wine refers to the more complex flavour compounds that evolve as a result of fermentation, élevage and ageing. With the exception of terpenes in aromatic grape varieties and alkoxypyrazines in herbaceous cultivars, perceived flavour is the result of the absolute amounts and specific ratios of many of these interactive compounds, rather than being attributable to a single “impact” compound. Without underestimating the complexity of these interactive effects or negating the definitive role played by accumulated secondary grape metabolites in the varietal character of wine, this review focuses mainly on the contribution of yeast fermentation to the sensorial quality of the final product. Yeast and fermentation conditions are considered among the most important factors influencing wine flavour. Both spontaneous and inoculated wine fermentations are affected by the diversity of yeasts associated with the vineyard and winery. During the primary alcoholic fermentation of sugar, the wine yeast Saccharomyces cerevisiae, together with other indigenous non-Saccharomyces species, produces ethanol, carbon dioxide and a number of by-products. Of these yeast-derived metabolites, alcohols, acetates and C4–C8 fatty acid ethyl esters are found at the highest concentrations in wine. While volatile metabolites contribute to the fermentation bouquet ubiquitous in all young wines, the production levels of these by-products are variable and strain-specific. Therefore, this article also highlights the importance of tapping into the hidden wealth of indigenous yeast species present on grapes, as well as the selection and genetic development of yeast starter-culture strains with improved flavour profiles. In the future, some winemakers may prefer to use mixtures of indigenous yeast species and tailored S. cerevisiae strains as starter cultures to reflect the biodiversity and stylistic distinctiveness of a given region. This will help winemakers meet consumers’ demand for individual wines with an intact local character and ensure the survival of wine’s most enthralling aspect - its endless variety.