Are We Misdescribing Astringency by Referring to Tannins?

tannin moleculeMost reviews of red wine include a brief description of mouthfeel, usually by referencing the impact and quality of tannins. Tannins are phenols extracted from skins, seeds, and oak barrels that cause the drying sensation, aka astringency, that is more apparent as the wine evolves in the mouth becoming especially salient on the finish. In white wines, in which the juice is not allowed to rest on the skins, however, tannins are much less present and astringency is seldom mentioned in tasting notes.

But the more I read about mouthfeel, the more it becomes apparent that other components of the wine also cause astringency including acidity. Here is the conclusion of a study on the effects of various wine components on salivation. (see Chapter by Alvaro Peña-Neira)

Polysaccharides, ethanol, pH, and ionic concentration can influence salivary lubrication, both by influencing phenol–salivary protein binding and by directly reducing salivary viscosity.

Less salivary lubrication will cause the sensation of astringency.

Here is another paper exploring the perception of astringency in white wine (summarized here, see paper by Jackson):

An important factor influencing the perceived astringency of white wine is the typically low pH of the wine (Fig. 11.8). Hydrogen ions in the wine can affect protein hydration, as well as phenolic and protein ionization, thereby influencing both direct precipitation and via phenol–protein bonding. Precipitation of salivary proteins has been correlated with astringency and related sensations (Thomas and Lawless, 1995). Acidity (Peleg et al., 1998) and ethanol (Vidal, Courcoux et al., 2004) enhance the perception of astringency.

And this study is focused on the perception of astringency in red wines:

As ethanol level and pH values increased, the astringency perception was lowered. While pH affected only astringency, ethanol contributed also to the perceived bitterness of tannin oligomers, especially at typical wine ethanol levels (11–15%).

(Remember that higher pH means the solution is more alkaline and thus more weakly acidic. Lower pH means the solution is less alkaline and more strongly acidic.)

I take away from these studies the observation that the drying sensation in red wines is not only from tannins but from other components of the wine, especially acidity. And the drying sensation in white wines, which is largely caused by acidity, should not be ignored because it is a different sensation from the sharp bite, increased salivation, and refreshing quality of the acidity usually referenced in tasting notes.

We use “tannins” as a short hand reference to astringency but that is probably misleading. And in white wines we tend to not mention astringency because it is assumed that tannins are not a factor. That is doubly misleading. Some white wines do have tannins, and astringency from acidity and alcohol also play a role in their mouthfeel. It probably should not go unmentioned.

It’s not clear to me if the perceived astringency from tannins differs from the perceived astringency of acid and alcohol. Since the mechanism is in all cases less salivary lubrication, I doubt they can be distinguished. But that is speculation on my part.

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