The distinctive sensation of tannins on the tongue will be familiar (overfamiliar, perhaps?) to many arXivblog readers.

And if you’ve ever wondered what causes that mouth-puckering dryness, you now have an answer thanks to the dedicated and selfless work of Drazen Zanchi and colleagues at the Laboratoire de Physique Théorique et Hautes Energies in Paris.

Tannins are large molecules with aromatic rings and OH groups which naturally bind to each other and to proteins, while repelling water. So the presence of tannins causes proteins to aggregate together. From the biological point of view, that makes good sense. Tannins are part of plants’ defence systems against the proteins that bacteria, viruses and higher herbivores secrete when invading. It takes these proteins out of action be forcing them to aggrgegate together.

Zanchi says exactly this process is responsible for the mouthfeel of tannins. Tannins bind to salivary proteins in the mouth making them aggregate and this causes a rapid and immediate drop in the viscosity of saliva. That’s why your mouth feels dry as you gulp sip your favourite oak-matured cab before after work every day.

Obviously, the strength of this effect and the size of the aggregates that form determine the mouthfeel of the wine.

So feel free to raise a glass to Zanchi and his pals next time you get a chance (which shouldn’t be too long now). Not least because this effect may turn out to have other uses.

The team say that attaching tannins to a surface could force proteins to aggregate at that site. Sounds handy. And they’re convinced they have only scratched the surface of a rich, untapped and largely undiscovered chemistry of tannin behaviour.

Ref: http://arxiv.org/abs/0810.1136: Colloidal Stability of Tannins: Astringency, Wine Tasting and Beyond