Tannins – their measurement and role as grape and wine quality indicators
Lambrechts, M G
Van Rensburg, P
Botes, M P
Lambrechts, M G
Current routine measurements used to define red grape maturity and quality are not providing viticulturists and wine makers with clear answers. The Distell 1 project was a first attempt to address this problem by focusing on anthocyanin measurements (red grape colour) as an additional quality parameter. Anthocyanins can only serve as an indirect indicator of grape and wine aroma and mouth-feel, since anthocyanins has been described as tasteless and non-astringent. The astringency, bitterness, dryness and mouth-feel in red wine is due to the presence of tannins and thus play an important role in the ultimate wine quality and style. However, robust scientific data on structures and properties of wine tannins are limited, a suitable standard tannin maturity has yet to be discovered and the compounds behind sensory sensations such as ‘green tannins’ remain to be established. This limited knowledge is due to methods not being specific enough and new methods that have been developed only recently. It is also clear from literature that there is consensus that tannin biosynthesis occurs prior to veraison, but the effects of viticultural treatments, seasonal variation and ‘terroir’ effects are less clear. Furthermore, the concentration of wine tannins is affected by grape maturity, tannin extractability and winemaking practices. It has also been shown that only a small portion of grape tannins are measured in the respective wine. The above raise many questions with regards to winemaking practices such as when to add tannins, micro-oxygenation, pomace contact etc. Therefore, to be able to measure red grape and wine tannins routinely and accurately should help us significantly in our quest to continuously improve our understanding of the correlation among grape composition, wine composition, style and quality.
The ultimate aim of this project is to incorporate tannin measurements as an additional red grape quality parameter and to optimise winemaking practices according to tannin measurements.