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This thesis focuses on the sources of tannin in Pinot Noir grapes. Tannins contribute to colour stability and mouth-feel in wine. Some tannins are more beneficial to the quality of red wines than others. Achieving the correct balance is particularly difficult in Pinot Noir wines due to their unusual polyphenolic profile. In practical terms the thesis considered the following questions: How do we know from which berry tissues wine tannins are extracted? Are some tannins more desirable than others from a wine composition and quality viewpoint? How can we get more of the desirable tannins into Pinot noir wines? The study sought to gain a better understanding of the types of phenolic compounds that influence wine quality in terms of colour stability. Phenolic compounds are mainly derived from the skin and seed of the grapes. However the nature and proportion of phenolic compounds that are contributed by each tissue type, and ultimately become incorporated into the wine, was largely unknown prior to this study. The trials reported in this thesis used micro-vinification vessels ranging in size from 0.25 to 20 L according to the detail of the experiment under investigation and the analyses applied. Maceration techniques that are practiced commercially were compared and showed that some of these are better suited to the production of Pinot Noir table wines than are others. To ascertain why this might be so, the research went on to examine the specific role of individual berry tissues in determining the outcome of the phenolic composition of the wine. The value of each tissue type was accentuated by providing a surplus or a deficit of each tissue type in the grape musts. The research examined the specific role of individual berry tissues in determining the outcome of the phenolic composition of the wine. A novel maceration technique (Accentuated Cut Edges or ACE) that improved the extraction of colour pigments from grape skin was examined in detail and strong correlations between the phenolic profile of the wine and its sensory attributes were identified. Finally, the spectral assessment of wine phenolic parameters from 15 individual experiments recognised six wavelengths by which phenolic components from skin and seed tissues could be distinguished. Using an existing rapid spectral assay, an index of phenolic quality was developed which has the potential to inform fermentation management strategies based on qualitative measures taken as the fermentation progresses. |
