Defining the mechanisms and impact of winemaking treatments on tannin and polysaccharides in red wine: recent progress in creating diverse styles

Abstract

Tannin and polysaccharide concentration and composition is important in defining the texture of red wines, but can vary due to factors such as cultivar, region, grape ripeness, viticultural practices and winemaking techniques. However, the concentration and composition of these macromolecules is dependent not only on grape tannin and polysaccharide concentration and composition, but also their extractability and, in the case of polysaccharides, their formation by yeast. Through studies into the influence of grape maturity, winemaking and sensory impacts of red grape polysaccharides, seed and skin tannins, recent research in our laboratory has shown that the processes involved in the extraction of these macromolecules from grapes and their retention in wine are very complex. In particular, the isolation and characterisation of polysaccharides and cell wall material (fibre) has shown that grape cell wall material (CWM) can bind tannins and modify the amount and type of tannins retained in wine. The action of enzymes, yeast and certain winemaking treatments on cell wall material can also profoundly influence the amount and types of polysaccharides retained in wine.These recent advances present new factors for consideration in grape selection and processing during winemaking which allow winemakers to more rigorously control colour and mouth-feel in red wines. This presentation with summarise recent studies in our laboratory that have focused on evaluating yeast strains and maceration processes during winemaking as tools to alter wine macromolecule concentration and composition. In wine made in the 2014 vintage it was found that the choice of yeast strain (10 yeast strains were benchmarked) resulted in highly variable polysaccharide and tannin concentrations. At the end of primary fermentation, the two yeasts which yielded highest wine tannin concentrations (1.5 g/L) resulted in wine with the lowest (0.45 g/L) and highest (0.66 g/L) polysaccharide concentrations respectively. It was found that the wine with the highest polysaccharide and tannin was associated with a transient release of pectic polysaccharides rich in galacturonic acid and arabinose from the grapes, suggesting pectolytic activity in yeast. Based on leads from this trial, in 2015 an experiment was performed to investigate the interactive effect of maceration time (7 vs 30 days), macerating enzyme and yeast strains (‘high-tannin’ vs ‘low-tannin’ yeast) on wine macromolecules in 50 kg Shiraz ferments. At 30 days, post maceration, no effect of yeast strain on polysaccharide concentration or composition was observed, although strong effects were found for enzyme application and maceration time. Results also show the combined use of yeast strain and maceration techniques can have a marked effect on wine tannin, but 30dM achieved the most significant shift in tannin concentration and molecular mass. The mechanisms by which these effects may occur will also be presented.