03 · Making Enthusiast

What oak does to wine

Barrels, flavour and texture: how ageing in wood changes wine at a chemical level, what it tastes like, and how to spot it in the glass.

Five things oak does

Flavour compounds

Oak staves contain vanillin (vanilla), lactones (coconut), guaiacol (smoke, clove), and furfural (almond, caramel). These compounds dissolve into wine during maturation. New oak imparts more than old; smaller barrels more than large.

Micro-oxygenation

Wood is porous. A tiny amount of oxygen passes through the staves into the wine over months. This softens harsh tannin by promoting polymerisation — tannin chains bind together and precipitate out, leaving the wine rounder.

Tannin extraction

Oak wood contains ellagitannins — a different type of tannin from grape-skin tannins. These dissolve into wine and contribute structure and texture. Oak tannins are generally smoother and less astringent than grape tannins.

Evaporation

About 2–3% of barrel contents evaporate annually through the wood (the "angel's share"). This concentrates the remaining wine — increasing flavour intensity, body and alcohol proportionally.

Reduction of acidity

Malolactic fermentation (MLF) often occurs during barrel ageing. This bacterial process converts sharp malic acid to softer lactic acid, reducing perceived acidity and adding a creamy, buttery texture, especially in Chardonnay.

Barrel size and toast level

A standard Bordeaux barrel (barrique) holds 225 litres. A Burgundy barrel (pièce) holds 228 litres. A large Slovenian oak cask (used in Barolo) holds 5,000–10,000 litres. The smaller the barrel relative to its wine volume, the more oak surface area contacts the wine — and the more flavour and micro-oxygenation it delivers. This is why small new-oak barriques have such a pronounced influence.

During cooperage, the inside of the barrel is toasted over an open flame. Light toast preserves more wood tannin and vanilla; medium toast balances flavour compounds and reduces harsh tannins; heavy toast adds smoke, coffee and caramel flavours. Most fine wine uses medium-toast barrels; heavily toasted barrels are common in bolder New World reds.

When to choose un-oaked

Un-oaked wines — fermented and aged in stainless steel, concrete or neutral large-format wood — preserve primary fruit character: the grape's own flavours of citrus, stone fruit or berry. This is why Chablis is unoaked (the mineral, saline character of the Kimmeridgian soil is the point), and why light aromatic whites like Riesling and Sauvignon Blanc rarely see oak. Oak would overwhelm their delicacy.

For more on how oak interacts with tannin, see the tannin glossary entry. For how it fits into the broader winemaking process, see the How wine is made guide.

Sources: WSET (winemaking and oak chemistry curricula), OIV (oenological practice standards), AWRI (oak and micro-oxygenation research), ACS Publications (vanillin and ellagitannin chemistry peer-reviewed research). Last updated: 2026-10-15. Corrections via the contact form.

Questions

About oak and wine.

How can I tell if a wine has been aged in oak?

The clearest indicators in the glass are: vanilla and toast aromas (compounds from the wood itself), a rounder, creamier texture on the palate (from micro-oxygenation and possible MLF), and a longer, slightly spicy or smoky finish. In white wines, oak ageing often shows as butterscotch or golden apple notes alongside the fruit. In reds, it softens the edges of tannin and adds a cedar or pencil-shaving quality. The label may say "aged in oak" or "élevé en fût de chêne" (French), but many labels are silent on the point.

What is the difference between new and old oak?

New oak barrels are used for the first time on a wine and impart strong flavour — significant vanilla, toast and spice. With each subsequent use, the barrel gives progressively less flavour (roughly halving with each use). By the fourth or fifth year, a barrel imparts almost no flavour at all, functioning mainly as a vessel for micro-oxygenation. Many quality producers use a mix of new and older barrels to balance flavour addition with oxidative ageing.

What is the difference between French and American oak?

French oak (Quercus petraea) has a tighter grain, imparting flavour more slowly and subtly — cedar, spice, nutmeg, fine-grain tannin. American oak (Quercus alba) has a wider grain, releasing flavour faster and more intensely — pronounced vanilla, coconut, dill. American oak is cheaper and historically dominant in Spanish Rioja, traditional Rioja and many Californian wines. French oak is used in Burgundy and Bordeaux, and increasingly worldwide for premium wines. Barrels from Slavonia (Croatia) are also common in Italian winemaking.

What are oak chips and staves?

Oak chips and staves (planks of oak) can be added to stainless steel or concrete tanks to impart oak flavour without the cost or logistic complexity of barrels. A barrel costs €700–1,500 and requires a cellar and skilled management; chips cost a fraction and can be added to any tank. Chips impart flavour without micro-oxygenation, producing a flavour profile that lacks the texture development of barrel ageing. This is legal in most wine-producing countries for non-appellation wines; EU appellation wines must be barrel-aged if they claim oak. The EU wine regulation (2019/33) lists all permitted oenological practices including the use of oak fragments.

Is un-oaked wine always lighter than oaked?

Not necessarily — body is driven primarily by alcohol and extract, not oak. An un-oaked Chardonnay from a warm climate at 14% ABV will be full-bodied even without a barrel. What oak adds is texture and specific flavour compounds, not body per se. A leaner un-oaked Chablis at 12.5% may taste lighter than a full-oaked Napa Chardonnay at 14.5%, but the difference is as much about climate and yield as about oak.