🍷 Wine taste and composition

Wine taste and composition are about the substances found in wine and the sensations they create: alcohol, acids, tannins, sugars, pigments and aroma compounds. Their balance is what sets one wine apart from another.

It all starts with the juice of ripe grapes: about 74% water, 25% sugars (fructose and glucose in roughly equal parts), 0.8% organic acids and 0.5% minerals, mostly potassium. Yeasts ferment the sugar, and under EU rules Alcohol in wine usually ranges from 8.5–9% to 15% by volume; Port typically has 19–22%.

Acidity in grapes comes mainly from tartaric and malic acids, which together make up more than 90% of all acids. In the EU a wine's total acidity cannot be lower than 3.5 g/l. Malolactic fermentation softens the taste by turning malic acid into lactic acid.

Tannins are responsible for astringency: they bind to saliva proteins and drop out with them, so the mouth loses its sense of lubrication. There are hydrolysable tannins, mostly from oak, and condensed tannins from the grape. Polyphenols average 1,545 mg/l in red wine but only 108 mg/l in white. Wine colour in red wines comes from anthocyanins in the grape skin; the main one is malvidin, and with age they turn into more stable pigments.

Glycerol, a by-product of fermentation, is usually present at 1–15 g/l, around 7 g/l on average. It has no smell but adds sweetness, softness and fullness. Wine aroma is divided into primary (from the grape), secondary (from winemaking: fermentation, oak, lees) and tertiary (from ageing). The Tears of wine on the glass are explained by the Marangoni effect: alcohol evaporates from the thin film, and the difference in surface tension pulls the liquid upwards.