Effects of aspects of terroir on the phenolic composition of New Zealand Pinot noir wines

Abstract

Phenolic content is an important dimension of Pinot noir wine quality. This study aimed to find generic relationships between the phenolic content of Pinot noir wines produced from well-defined locations (single vineyards) in New Zealand, as determined from various chemical analyses, and aspects of terroir relating to local climate, soils and methods of production and information collected from questionnaires. Two New Zealand Pinot noir wines were stored at room temperature (with and without headspace sparging with N₂), at 4°C (with and without sparged N₂), at - 20°C, and at - 80°C following flash freezing with liquid nitrogen, after the original, sealed bottles were opened. The changes in total phenolics, total tannins, anthocyanins and colour parameters over 134 days were quantified. Results showed that the colour-related parameters were more sensitive to storage conditions and time compared with the other parameters. Storage at - 80°C could be the optimal way to preserve colour parameters, as it generally caused the least change in values and induced the least precipitation over the whole experimental period, followed by storage at 4°C. A total of 86 single-vineyard Pinot noir wines were collected from the 2013 Bragato wine competition. Analyses, using standard methods for total phenolics, total tannins and colour measurements, and HPLC (high-performance liquid chromatography) analysis of monomeric species separated using a published SPE (solid-phase extraction) method, were carried out on these wines. Some strong correlations were found between the different ways of taking measurements on the same, or similar, compounds in wines. Generally, the regional or vintage differences in total phenolics content and total tannins, were not dramatic, but there were evident regional and vintage differences in the colour parameters. Wines awarded different medals grades also differed in their colour parameters. Specifically, wines with gold or silver medals tended to have deeper colour densities and were higher in total anthocyanins than the bronze and no-medal wines, but were not necessarily lower in colour hue. The overall phenolic content differences investigated using PCA (principal component analysis), showed separations between Otago wines and Marlborough wines, and also between vintage 2012 wines, 2011 wines and 2010 wines, although there were some overlaps in these separations. A total of 41 viable questionnaires were returned. Viticulture, winemaking and barrel ageing practices were all quite similar among wines and influences for these parameters on individual phenolics were not able to be drawn. In contrast, soils differed considerably between regions and there were consistent negative and linear correlations between vine potential vigour as affected by soil parameters (carbon content, potential rooting depth and profile readily available water) and key colour parameters (total anthocyanins, total red pigments, ionised anthocyanins, and malvidin-3-glucoside), while positive correlations with some hydroxybenzoic acids were also found.