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The effect of pre- and post-ferment additions of grape derived tannin on Shiraz wine sensory properties and phenolic composition


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To assess the effects of exogenous tannin addition on the properties of a red wine made from Vitis vinifera cv. Shiraz, a winemaking study was performed with pre- and post-alcoholic fermentation additions of 200 mg/L of a commercial grape seed-derived oenotannin product. The influence of the added oenotannin on wine tannin concentration, pigmented polymer concentration and colour parameters was monitored throughout the winemaking process and for up to two years of post-bottling storage. Additionally, after one year of storage, the in-mouth sensory attributes of the wines were characterised using sensory descriptive analysis. No significant differences in wine colour properties and pigment profiles were found between treatments. Tannin concentration as measured by HPLC was not significantly different at the end of the experiment, but when considered over the whole time-course it was significantly higher in the post-ferment treatment. The magnitude of the effect on astringency of the oenotannin addition at 200 mg/L during winemaking was small and the sensory response was the same regardless of addition pre- or post-fermentation. The magnitude of the sensory response to the wines was not significantly different from that of the control wine assessed after (i) 200 mg/L of the oenotannin was added immediately prior to sensory evaluation, or (ii) addition of 200 mg/L of two other commercial tannin preparations. For the type of red wine and oenotannin studied, tannin addition did not affect wine colour properties and had only a minor effect on perceived astringency.