Winemaking practice affects the extraction of smoke‐borne phenols from grapes into wines

Abstract

Background and Aims: Exposure to smoke and uptake of taint imparting phenols in grapes and wines is a significant problem in bushfire-prone regions of Australia and other countries. The effects of smoke exposure on taint occurrence in wines, however, can be variable. This study assessed the influence of cultivar on uptake and accumulation of smoke-borne phenols in grapes and of subsequent processing and winemaking methods on extraction of phenols into wines. Methods and Results: Smoke-exposure experiments were conducted in commercial vineyards of Chardonnay, Merlot and Sauvignon Blanc 14 days after the onset of veraison. At maturity, grapes were harvested for winemaking, which included malolactic fermentation (MLF) for Merlot. Volatile and glycoconjugated phenols were determined in grapes and the resultant wines. All cultivars had a similar concentration of smoke-derived total phenols in their grapes. The apparent extraction of total phenols from grapes into wines, however, differed markedly among the three traditional winemaking methods. Red winemaking (Merlot) with skin contact extracted 88% of total grape phenols, whereas white winemaking either by crushing before pressing (Sauvignon Blanc) or by whole-bunch pressing without crushing (Chardonnay), respectively, released 39 and 18% of total phenols. For Merlot wines, MLF did not affect the extraction of total smoke-derived phenols. Conclusions: Under standardised exposure conditions (duration, intensity and phenology), the three cultivars studied accumulated a similar concentration of total phenols in grapes. The grape-processing and winemaking methods, however, can bring about a fourfold difference in the concentration of total phenols of wines. The smoke-derived phenols extracted from grapes into wine and the distribution of these phenols between the volatile and conjugated pools were not affected by MLF. Significance of the Study: The key findings reported here have the potential to improve decision-making by grapegrowers and winemakers on the effect of cultivar and winemaking practice on potential smoke taint in wine.