The mechanism by which astringency is perceived is unknown. Two different mechanisms have been proposed.
- The ASTM defines astringency as the puckering or constricting of the oral epithelial tissue, suggesting that a morphological change occurs when an astringent system is evaluated.
- In contrast, others hypothesize that the rough feeling of astringency occurs when salivary proteins bind to tannins, oral lubrication decreases and friction (roughness) is perceived.
Preliminarily, from our study of the morphological changes in the epithelial mucosa, it appears that astringency does not result from “constriction of the oral tissue”. No obvious differences in distances between epithelial cells were observed after application of astringents. However, it is possible that the loose cells on the surface slough off after binding with tannins, perhaps resulting in perception of astringency, but this has not been substantiated.
Consistent with the second hypothesis, in previous studies, it has been shown that individuals with low flow rates of saliva perceive astringency more intensely and longer than high-flow subjects. To confirm this effect of salivary flow rate independent of variation in use of the intensity rating scale, artificial saliva was introduced to the judge’s mouth at different flow rates. Astringency was rated lower at high flow rates of application than when lower rates of application were used. In both cases, comparison of individuals with different flow rates and with the application of artificial saliva at varying flow rates, the presumption has been that astringency decreases at a higher flow rate due to restoration of lubrication. However, no difference in astringency was found between application of artificial saliva with protein vs. an artificial saliva containing no protein. These results suggest that higher salivary flow rates may dilute or more thoroughly flush the mouth, and suggest that further research into the mechanism of astringency is needed.
The persistence of astringency has been recognized but only recently has the carry-over effect been documented in which each sip of wine influences the astringency perceived in subsequent sips or wines. For meaningful evaluations of astringent red wines during winemaking, blending or in competitions a tasting protocol to remove or reduce the buildup of astringency must be developed. To do this, astringency was rated continuously while red wines were sipped, spit, and judges rinsed with one of 5 solutions. A pectin rinse reduced astringency intensity significantly more than the other rinses. We are presently investigating the most effective way to prevent the increase in intensity for wines varying in astringency level and to define the minimum time to recommend between wines.