Tannin is described in tasting notes as though it were a flavour, but it registers through touch rather than taste. Understanding that changes how it should be assessed.
The mechanism is protein binding
Tannins are polyphenolic compounds that bind readily to proteins. Saliva is rich in lubricating proteins, and tannin latches onto them and precipitates them out of suspension.
The result is that the mouth briefly loses its film of lubrication, producing the dry, grippy sensation felt across the gums and the sides of the tongue. Nothing is being tasted at that moment.
Because this is a mechanical event rather than chemical detection by taste buds, tannin registers through the trigeminal nerve. That is the same system reporting texture, temperature and irritation.
Where tannin comes from in the first place
Grape skins, seeds and stems all contain tannin, and how long the juice sits in contact with them determines how much ends up in the wine.
White wines are usually pressed away from their skins immediately, which is the main reason they carry little tannin regardless of grape variety.
Oak barrels contribute a further tannin of a different character, generally finer grained and rounder than the tannin extracted from seeds.
Quality of tannin is about particle size
Tasters describe tannin as fine, grainy, chalky or coarse, and these terms track how the binding is distributed across the mouth.
Long polymerised tannin chains feel smooth and broad, while shorter, more reactive ones feel abrasive and localised.
Ageing gradually links tannin molecules into longer chains that eventually become too large to stay in solution. They fall out as sediment, and the wine softens.
Why food changes the reading completely
Protein in food offers tannin an alternative binding target, so tannin that grips harshly on its own becomes unobtrusive alongside a protein-rich dish.
Fat performs a similar job by coating the palate and slowing the interaction. This is the mechanism behind the oldest pairing convention in the book.
Assessing a tannic wine without food therefore gives a systematically harsher reading than the wine will deliver at a table.
Distinguishing tannin from acidity
Acidity produces salivation, and tannin removes it. The two sensations are opposites and can be separated by attending to what the mouth does afterwards.
A wine that makes the mouth water is acidic; one that leaves it feeling scoured is tannic. Many wines do both, in sequence.
Learning to separate them is the single most useful step in writing a tasting note that means something to another reader.