Factors affecting bitterness, astringency and mouthfeel in wine
The effect of varying sourness on perceived astringency has been studied using different astringents and different acids. Astringency of phenolic compounds (grape seed tannin, catechin, tannic acid or gallic acid) increases with increasing citric acid. Alum, in contrast, shows a very strong decrease in astringency with the addition of acid. The results of this experiment call into question basic sensory studies of astringency which have interchangeably used alum and other astringent compounds such as tannic acid. Astringency of alum was decreased equivalently by addition of lactic acid, citric acid or hydrochloric (HC1) acid. The acids themselves have different astringencies at equally sour concentrations. Citric acid was least sour, while lactic and HC1 were equal in astringency to the alum solution. In previous experiments, increasing sucrose concentration in red wine decreased both maximum intensity and total duration of astringency (Ishikawa and Noble, 1995). The role of the sweetness versus the contribution of viscosity of the added sucrose in reducing astringency was unknown. In the present experiments using the sweetener aspartame, increasing sweetness with no increase in viscosity resulted in no change in astringency, while the bitterness of the GST was slightly decreased. In contrast, as viscosity was increased, both maximum intensity (Imax) and total duration (TOT) of astringency of grape seed tannin (GST), citric acid and alum were significantly decreased. Sour Imax and TOT of citric acid and alum were also decreased as the viscosity was raised. In contrast, no change in bitter Imax and TOT of GST was perceived as viscosity was raised. These results suggest that perception of the astringency is influenced by tactile factors such as viscosity, more than by tastes. Continuing studies of the role of saliva in sensory perception, consistent with results found for thickened sweet solutions (AVF 94 final report), there was no difference in perception of astringency of thickened solutions of grape seed tannin between high- and low-flow judges. In contrast, perception of unthickened grape seed tannin solutions which contained no and increasing levels of aspartame, astringency was rated more intensely by the low flow subjects.