Glossary
Tannin
A group of phenolic compounds that bind with proteins in your saliva, producing a drying, slightly rough sensation across the gums. Tannin is a texture, not a flavour — it is felt rather than tasted.
In more detail
It comes mainly from grape skins and seeds, which is why red wines (fermented on their skins) have far more of it than whites.
Because it binds with protein, tannin is softened by fatty, protein-rich food. This is the mechanism behind steak and Cabernet.
Tannins polymerise into larger molecules over time, which is why an old wine feels softer than a young one.