noun (plural) From Greek phainein (to show) via the chemical compound phenol (C₆H₅OH); phenolic compounds are a broad class of organic molecules containing one or more hydroxyl groups attached to an aromatic ring

Phenolics /fɪˈnɒlɪks/

A broad class of organic compounds found in grapes and wine that includes tannins, anthocyanins (colour pigments), stilbenes, and numerous other polyphenols. Phenolics originate primarily in the grape's skins, seeds and stems; a smaller contribution comes from oak during barrel ageing. In wine, phenolics are responsible for colour (anthocyanins in red wine), structure and astringency (tannins), bitterness, and numerous aromatic compounds. The measure of phenolic maturity — when the grape's phenolic compounds have developed to their optimal composition and are in the right ratio of sugars and acidity — is called phenolic ripeness, distinct from physiological ripeness measured by sugar or acidity alone.

Six classes of wine phenolics

Class Source Role Notes

Tannins (grape) Skins, seeds, stems Structure, astringency, colour stability Condensed tannins (proanthocyanidins) from grape tissue. Seeds have harsher tannin than skins; stems add grippy, green tannin if included.

Tannins (oak) Oak barrel staves Structure, oxygen buffering, flavour Hydrolysable tannins (ellagitannins) from oak. Different structure to grape tannins. Interact with anthocyanins to stabilise colour.

Anthocyanins Red/black grape skins Colour (red, purple, blue-violet) The pigments that make red wine red. Unstable alone; bind with tannin during ageing (co-polymerisation) to form stable pigmented tannins.

Resveratrol Grape skins Antioxidant (in vivo) The polyphenol associated with wine's purported health benefits. Present in relatively small quantities in wine; whether wine consumption provides meaningful doses is debated.

Flavonols (quercetin etc.) Grape skins, particularly in high-UV sites UV protection, colour co-pigmentation Higher in grapes from high-altitude or high-UV vineyards. Contribute to colour co-pigmentation — the deepening of colour in red wine.

Hydroxycinnamic acids Pulp and skin Browning reactions, white wine colour The main phenolic class in white wine. Responsible for the browning that occurs in white wine with oxygen exposure. Caffeic acid is the most common.

Phenolics and wine colour

The red-to-purple colour of young red wine comes entirely from anthocyanins in the grape skins — the juice of red grape varieties is almost colourless. Anthocyanins are inherently unstable; without bonding to other molecules, they would degrade within months. During maceration and ageing, anthocyanins co-polymerise with tannins to form pigmented tannin complexes that are far more stable. These complexes accumulate in the wine as it ages, forming the dark sediment in old red wine. The colour of the wine shifts as this process progresses: the intense blue-purple of young red wine (free anthocyanins) gives way to garnet red (anthocyanin-tannin complexes) and eventually to the brick-orange rim of old wine (highly oxidised and polymerised complexes). The depth and stability of red wine colour are therefore a direct function of tannin-anthocyanin chemistry — which is why maceration management and phenolic ripeness at harvest are so critical to long-lived red wine. See tannin for the specific chemistry of tannin evolution.

Phenolics in white wine

White wine contains far fewer phenolics than red wine (because white grapes are pressed immediately without skin contact, limiting phenolic extraction). The primary phenolics in white wine are hydroxycinnamic acids (caffeic acid, ferulic acid, p-coumaric acid) from the grape pulp and skin. These are the compounds responsible for the browning that occurs in white wine with oxygen exposure — they are the white wine equivalent of cut apple turning brown. Winemakers limit this by pressing under inert gas, adding sulphur dioxide immediately at pressing (which inhibits the oxidative enzymes that catalyse browning), and using reductive handling throughout. Orange wine (skin-contact white) contains significantly more phenolics than conventional white wine — tannin and anthocyanins extracted during the skin contact period — which is why orange wines have the amber colour, textural grip and tannic structure absent from conventional whites. See maceration for how skin contact extracts phenolics from white grapes.

Sources: AWRI (Australian Wine Research Institute) (phenolic chemistry research); WSET (wine chemistry curricula, Level 4 Diploma); Jancis Robinson MW (Oxford Companion to Wine, phenolics). Last updated: 2026-10-22. Corrections via the contact form.

Questions

About phenolics.

What is phenolic ripeness and how does it differ from sugar ripeness?

Phenolic ripeness refers to the maturity of the phenolic compounds in the grape — particularly the tannins in the skins and seeds, which undergo fundamental structural changes as the grape ripens. Early in the season, grape tannins are harsh, astringent, and "green" — the seeds are hard and the skin tannins are rough and drying. As the grape ripens, the seed tannins become less harsh and the skin tannins become softer, rounder and more easily extracted. "Phenolic ripeness" is achieved when the tannins are ripe — extractable without excessive harshness — and the anthocyanins are fully developed. This can occur at a different time from sugar ripeness (when sugar levels are sufficient for the desired alcohol) and physiological ripeness (when the grape's texture, seed colour and flavour suggest maturity). In warm climates, sugar ripeness often arrives before phenolic ripeness; this is one reason wines from hot vintages or over-cropped vines can have high alcohol but green, harsh tannin. Winemakers in quality-focused regions aim to harvest at phenolic ripeness, which may require accepting high sugar levels (and therefore high alcohol, or the need for chaptalization in reverse — de-alcoholisation). See phenolic ripeness glossary entry for the full definition.

Are phenolics the same as antioxidants in wine?

Many phenolics are antioxidants in the chemical sense — they can donate electrons to reactive oxygen species, neutralising them — and this is the basis of the health claims made about wine, particularly red wine. Resveratrol (a stilbene phenolic in grape skins) became famous in the 1990s as a candidate explanation for the "French paradox" — the apparently lower rate of cardiovascular disease in France despite a high-fat diet. The problem: resveratrol and other phenolics are present in wine in relatively modest concentrations; to consume the dose used in laboratory studies showing cardiovascular benefit, a person would need to drink several litres of wine per day. More importantly, the epidemiological studies associating moderate wine consumption with health benefits have been substantially challenged — the methodology typically did not control for other lifestyle factors associated with moderate wine drinking. The current scientific consensus is that any health benefit from wine's phenolics is likely minimal at typical consumption levels, and that the harms of alcohol consumption outweigh the putative phenolic benefits. Phenolics are important for wine quality and structure; their health significance is much less certain than popular coverage suggests.

How do phenolics change as wine ages?

The evolution of phenolics during wine ageing is one of the central processes of wine development. In red wine, the most important changes: anthocyanins (the unstable red pigments) bind with tannins through co-polymerisation to form stable pigmented polymers — this is what causes red wine colour to shift from purple-red in youth to garnet and eventually tawny-brick with age, and what makes tannins softer over time (the polymers are too large to bind to salivary proteins as effectively). Tannins polymerise (join together into longer chains), producing softer, less aggressive astringency — the "silky" texture of aged Barolo or Bordeaux. The wine gradually deposits dark sediment (polymerised tannin-anthocyanin complexes) as these large molecules become too large to remain in solution. In white wine, phenolic evolution is primarily about oxidation of hydroxycinnamic acids (colour deepens from pale yellow to gold to amber) and the loss of primary aromatic phenolics. Oxygen management throughout the wine's life significantly affects the rate and direction of phenolic evolution.

What is the difference between phenolics from grapes and from oak?

Grape phenolics (condensed tannins, anthocyanins, flavonols) and oak phenolics (hydrolysable tannins, ellagitannins) are structurally distinct and behave differently in wine. Grape tannins are condensed tannins — built from flavan-3-ol monomers (catechin, epicatechin) joined by carbon-carbon bonds. They are relatively resistant to hydrolysis (breakdown by water) and are the primary structural tannins in wine. Oak tannins are hydrolysable tannins — based on gallic acid and ellagic acid attached to glucose, which break down more readily in water and acid solutions. They interact with anthocyanins differently from grape tannins, contributing to colour stability through distinct co-pigmentation mechanisms. Practically: oak tannins add a different textural dimension from grape tannins — sometimes described as "dustier" or "firmer" in character — and contribute to the overall phenolic complexity of oak-aged wine alongside the volatile flavour compounds (vanillin, eugenol, lactones) that oak releases. The interaction between grape tannins and oak tannins in barrel-aged red wine is part of what creates the complex, layered structure of fine aged red wine.