Why are some wines aged in oak barrels?

Oak has been part of winemaking since the Gauls replaced Roman clay amphorae with wooden barrels. Today, barrel ageing is a deliberate winemaking choice that shapes a wine's aroma, texture and longevity.

Three things happen inside an oak barrel. First, flavour extraction: the wood releases compounds including vanillin (vanilla), lactones (coconut), guaiacol (smoke) and eugenol (clove). The intensity depends on how heavily the barrel was toasted and whether it is new or has been used before — a brand-new barrel imparts far more character than one on its third fill. Second, micro-oxygenation: oak is slightly porous, allowing tiny amounts of oxygen to reach the wine, which polymerises tannins and makes them silkier. Third, evaporation — the so-called "angel's share" — concentrates the wine by around 2–5% per year.

The type of oak matters enormously. French oak from forests like Allier, Tronçais or the Vosges delivers fine-grained tannins and subtle spice, while American oak provides bolder vanilla and coconut flavours. Barrel size also plays a role: a standard 225-litre Bordeaux barrique exposes more wine to wood surface than a 2,000-litre foudre, resulting in a stronger oak influence.

Not every wine benefits from oak. Crisp, aromatic whites such as Riesling and Sauvignon Blanc are typically fermented in stainless steel to preserve fruit purity. Oak ageing is most common for age-worthy reds — Bordeaux, Barolo, Rioja — and for premium Burgundy Chardonnay.