🍷 Tannins

Tannins are polyphenolic substances that make the mouth feel dry, puckered and rough. In grapes they occur in the skins, seeds and stems; these condensed tannins, or proanthocyanidins, form the structure, or body, of red wine. Astringency is considered an important quality trait of red wine in particular. ¹

Red versus white. In a Czech study of 29 wines, the reds averaged 1545 mg/l of phenolic compounds and the whites 108 mg/l. Flavonoids made up over 85% of the phenolics in red wine and under 20% in white, and tannins are rarely found in white wines. So noticeable astringency is above all a feature of red wine. ³

How tannins dry the mouth. Tannins bind to salivary proteins, mainly proline-rich proteins and histatins. The complexes aggregate and precipitate, saliva becomes less slippery and friction in the mouth rises, which is felt as dryness and graininess. ¹

Skin and seed tannins. Skin tannins are long chains of 3–83 units built from procyanidins and prodelphinidins, with only 3–6% galloylated units. Seed tannins are shorter, 2–17 units, made mostly of catechin and epicatechin and 13–29% galloylated. Their smaller size may explain their bitterness, which is why seed tannins are considered undesirable. ¹

Maceration decides. Skin tannins pass into the wine first, and seed tannins later as fermentation continues. In a Cabernet Sauvignon study, skin tannins peaked by the first sampling, while large seed tannins kept increasing for up to 20 days, and the astringency and bitterness of seed extracts grew with time. In industrial tanks tannins increased up to 12.7% alcohol, about 9 days of maceration. ¹²

Balance on the palate. Astringency is pleasant when it is balanced by alcohol and sugar. When tannins and acids outweigh sugar, wine seems harsh, unripe or «green», while too much sugar makes it «thick» or flabby. Polysaccharides, residual sugar, anthocyanins, acidity and alcohol all affect astringency too. ¹

Colour and ageing. Tannins combine with anthocyanins into polymeric pigments that affect the colour stability of red wine during ageing, and yeasts influence their formation. ⁴ Tannins from aged wines carry more incorporated anthocyanins than those from young wines, which partly explains why anthocyanins decline as wine ages. ¹

Oak and added tannins. During ageing, oak barrels or chips release a small share of hydrolysable tannins, but on their own these are unlikely to affect astringency much. ¹ The OIV allows tannins to be added to wine to aid stabilisation and fining, protect it from oxidation and support the colour of red wines; such tannins must meet the International Oenological Codex. ⁵

Why it matters to you. Strong astringency in red wine comes from skin and seed tannins, and longer maceration usually makes a wine more astringent and bitter. ¹² If you dislike the drying feel, choose wines with balanced astringency, or whites, which have hardly any tannin. ³