Tannin in wine
Tannin is the astringent substance in wine: a group of polyphenols that come mainly from grape skins, seeds and stems and, during ageing in wooden barrels, are supplemented by barrel tannins. In the mouth you do not taste tannin in the strict sense, you feel it — as grip, dryness or a furry pull. This sensation arises because tannins bind to the proteins in saliva and temporarily remove its lubricating film. How much tannin a wine carries, and in what condition, helps decide how long it will keep and what it goes with at the table.
Where the tannin comes from
The amount and type of tannin are largely decided in the vineyard and merely dosed in the cellar. The skins yield the softer, more textile tannins, the seeds the more angular ones, and the stems — if fermented along with the grapes — a cool, green note. Thick-skinned varieties such as Cabernet Sauvignon naturally bring more of it than Merlot, which is why a cuvée with a high proportion of Cabernet usually seems sterner in its youth. In the cellar, destemming, maceration time and the handling of the press wine then determine how much of this potential actually passes into the finished wine.
Why the mouth feels dry
Astringency is not a taste but a tactile sensation. Tannins attach to the proline-rich proteins in saliva that otherwise coat the palate; once this lubricating film is gone, tongue rubs against palate and the mouth feels rough. Bitterness is something else: it is tasted on the tongue and usually comes from smaller phenolic molecules. Because the two can occur together, a wine with unripe tannin often seems not only hard but bitter as well. How these sensations combine into a mouthfeel is something we describe in the context piece on texture.
Ripe tannin begins in the vineyard
Whether tannin later tastes velvety or scratchy depends less on its quantity than on its degree of ripeness. Sugar ripeness and phenolic ripeness do not run in sync: a must can be analytically ready while the seeds are still green and their tannins correspondingly hard. We therefore set the harvest date plot by plot according to phenolic ripeness, accepting in return that individual sites are picked later than the sugar reading alone would suggest.
What time does to tannin
In the bottle, tannin molecules join with one another and with the pigments to form longer chains. Large molecules bind salivary proteins less readily, and so a wine seems softer over the years even though, arithmetically, hardly any tannin has disappeared. Beyond a certain size the chains no longer stay in solution and settle as sediment at the bottom of the bottle; a deposit in an older red wine thus shows that this rebuilding has taken place. This path is only reliable if the tannin was sound from the start — hard, green tannin does not become velvety even after ten years. That we only release our wines once they are ready to drink has one of its reasons here: the bottles spend the years in which this is decided with us.
Tannin at the table
What happens in the mouth can be put to use when eating. Protein and fat bind tannins before saliva does; a piece of beef or a mature hard cheese therefore noticeably takes the edge off a tannic wine, while a delicate fish dish disappears beneath it. Serving temperature plays its part too: poured too warm, alcohol and tannin come forward together and the wine seems harder than it is. Seen this way, tannin is less a quality one likes or dislikes than information about how a wine is built and when it shows best — it is worth reading it together with the other load-bearing elements that we describe in the context piece on structure.