Sensory Assessment of Astringency, Bitterness, and Aromatic Descriptors of Different Wine Tannin Formulations in Water Solution and Wine

Tannins are plant polyphenolic secondary metabolites that have the capacity to complex with salivary proteins and taste receptor membranes, affecting wine organoleptic sensations such as astringency, bitterness, and aromatic perceptions. In grape wine (Vitis vinifera), tannins can be extracted during winemaking as proanthocyanidins (PAs) primarily found in grape skins and seeds. Exogenous tannins can also be present in wines via enological practices such as the traditional oak barrel aging, or as commercially available products that are added during winemaking. Commercial enological tannins (CETs) are natural products extracted from different botanical sources as either relatively pure extracts of single species, or a mixture of species. Due to the great variation of CETs available in the market, results on their impact on wine sensory perceptions is still a matter of debate. A priori knowledge of the effects of specific CETs on wine quality is essential for production practices that lead to predictable results. The aim of this study was to compare different enological tannins produced by the same manufacturer added to water solution and to wine, in order to assess their effect on astringency, bitterness and aromatic sensations. Astringency perceptions ratings for tannin formulations in both water solution and wine were found to significantly vary. Grape seed PAs were rated as most astringent, while white grape skin PAs were rated as the least. Bitterness sensations were only perceived to be significantly different in tannin formulations in water, but not in wine. In water solutions, Quebracho wood PAs were perceived as the most bitter, while white grape skin PAs were found to be the least. Tannins extracted from white grape skin PAs were found to have the lowest significant astringency and bitterness perception ratings for all CETs in water solution. In terms of aromatic perceptions, the presence and frequency percentage of aroma descriptors perceived by panelists in wine changed with the addition of tannins as compared to wine alone. In general, similar aromatic descriptors were chosen for tannin formulations in water and in wine. It is interesting to note that every tannin formulation sample had at least one wood descriptor chosen, except for the ones extracted from Acacia PAs (Acacia mearnsii) in water solution.