Effects of pH, Acidity and Ethanol on Astringency and Bitterness of Grape Tannin in Model Wine Solution

Condensed tannins are the major compounds responsible for the sensory characteristics of bitterness and astringency in wine. However, these sensations are also influenced by many environmental factors in wine matrix. It is essential to understand the comprehensive effects of these factors on the bitterness and astringency of tannin as well as their interactions, which of practically importance for winemaker to control winemaking process and improve the quality of wines. Covering their typical concentration in wine, the combined effects of pH (2.8 - 3.8), acidity (tartaric acid, 1.6 - 8.0 g/L) and ethanol (3.8 - 14.0% vol) on the astringency and bitterness of grape tannin were investigated in a model wine by using the design of quadratic orthogonal rotating combination, and the regression models of test factors and the astringent intensity and the bitterness intensity were established respectively, with the individual and interactive of the factors analyzed. The results showed that pH was the major factor affecting the astringency of tannin, next was the acidity, while the ethanol had no effect. Among them, pH performed a negative effect, while the change curve of astringency with acidity was an open side down parabola. For the bitterness of tannin, ethanol was the most factor, next was acidity, and pH was the least. Ethanol had a positive effect, while acidity showed a negative effect. Under the experimental conditions, no significant interactive effect was found between the factors either for the bitterness or for the astringency of tannin.