Effect of vineyard management on the chemical composition of grape juice and wine

Abstract

The main aim of this study was to determine the impact of two contrasting viticultural practices, i.e., use (termed ‘Contemporary’) and no use (termed ‘Future’) of synthetic herbicides, on grape juice and wine chemical composition. Pinot noir, Merlot and Sauvignon blanc juice and wine samples were sourced from Marlborough and Hawke’s Bay. Key metabolites, such as amino acids, aroma compounds, and thiol precursors, were measured pre- and post-spontaneous fermentation in juice and wine samples originating from grapes collected from the different viticulture regimes. The resulting data sets showed that grape variety and vintage year were the most significant factors that influenced the juice and wine metabolites, followed by planting region and viticulture regime. Important metabolites that distinguished between vineyard management practices were determined from juice and wine data. The concentrations of 105 important compounds determined in juices from the Contemporary practice were generally higher than those of their Future counterparts. In addition, 221 important metabolites were identified and highlighted the influence of the viticulture regimes on the targeted wine metabolites. However, contrary to the juice samples, no consistent concentration trend was observed in the important metabolites of the finished wines. For the Sauvignon blanc wines, the vineyard regimes predominately contributed to the differences in aroma compounds, such as higher alcohols, monoterpenes, and C13-norisoprenoids in that their concentrations were higher under the Future regime. For the red wines, amino acids were the compounds most influenced, showing higher concentrations in the Future Merlot samples and Contemporary Pinot noir wines. Herbicide residue in grape juice, arising from herbicide application under the Contemporary regime, might play a direct role in the wild yeast strain populations in the juice and an indirect role in the metabolite concentrations during the spontaneous fermentation. In conclusion, a difference in juice and wine metabolite profiles between vineyard management regimes with and without herbicide application was detectable and significant. This information is valuable for grape growers and winemakers as the industry faces increasing scrutiny regarding the use of synthetic chemicals in viticulture.