Investigation of Mechanisms for Perception of Astringency
Astringency intensity increases progressively with sips, a protocol for measuring astringency in the sensory laboratory was developed which would optimally mimic normal wine drinking behavior. Sip volumes and times between sips of typical consumers were quantified. On the average, 10 ml of wine were sipped at 25 sec intervals, with the wine held in the mouth 3 sec before being swallowed. Using this information, the protocol for rating astringency continuously through four sips was implemented. Judges sipped 10-ml of red wine, swallowed 6 sec later, and sipped three more sips at 25 sec intervals to mimic a realistic pattern of wine consumption by normal consumers. Upon successive sips, a consistent increase in astringency was found. After each sip, the intensity of astringency increased continuously to a maximum (FIG. 2.2), and then decreased slightly, but the initial intensity values before ingestion increased with each sip. The first two sips produced larger increases in astringency for the more astringent wines. However for sips 3 and 4, the absolute increase in astringency per sip becomes more similar. These results have important implications for wineries testing the effects of variables such as maturity on astringency. Sipping several samples in a row can not provide valid information about the effect of the treatment. Thorough rinsing between wines is essential or a time intensity method could be used. It has been hypothesized that sensory perception of astringency is the result of tannins binding to salivary proteins. As a consequence, the effectiveness of salivary lubrication is decreased, and astringency is perceived as the friction between two “unlubricated” surfaces. In previous sensory studies, we demonstrated that increasing viscosity lowers astringency. This was hypothesized to occur due to restoration of lubrication. In the research conducted this year, the change in viscosity of saliva upon addition of tannin was measured. The viscosity of saliva decreased after reacting with tannin. Future research is needed to determine if the observed small viscosity change corresponds to a significant change in perception of astringency.