French oak barrels. How they are made, and what they do to wine.

Why French oak?

Most fine-wine barrels are made from two European oak species, mainly Quercus petraea (sessile oak), which grows slowly in forests such as Tronçais, Allier, Nevers and the Vosges. Slow growth gives a tight grain, and tight grain releases flavor and tannin gently.

American white oak (Quercus alba) is the other big option. It gives more obvious vanilla and coconut notes. French oak is usually described as more subtle and spicy, and it is the classic choice for Bordeaux, Burgundy and many top wines worldwide. Old-growth French oak is scarce, which is one reason these barrels are reserved for the most prestigious wines.

From tree to barrel

The oak is split, not sawn, along the grain into staves. The staves then season outdoors for two to three years, so rain, sun and fungi wash out harsh tannins. Only then does the cooper shape them.

The staves are raised into a barrel inside metal hoops and heated over a fire so they can be bent. That same fire “toasts” the inside of the barrel. A light toast keeps more fresh oak character, a medium or heavy toast brings notes of toast, coffee, caramel and spice. The classic Bordeaux barrique holds 225 liters; the Burgundian pièce holds 228.

What oak does to wine

A barrel works in three ways. It adds flavor: vanilla, cloves, toast and sweet spice from compounds in the wood. It adds tannin, which gives structure. And it lets in a tiny amount of oxygen, which softens tannins, stabilizes color and helps the wine develop.

A new barrel gives the most flavor. After three or four vintages it is almost neutral and mainly works through oxygen. That is why winemakers talk about the percentage of new oak: 100% new oak for a powerful Bordeaux, much less for a delicate Pinot Noir.

How to recognize oak in your glass

Aromas of vanilla, toast, coconut, cedar or smoke usually point to oak. On the palate, oak can make a wine feel rounder and more structured. In WSET terms, these are secondary aromas from winemaking, as opposed to the primary fruit aromas of the grape.

Too much new oak can mask the fruit; well-integrated oak supports it. That balance is one of the arts of the winemaker.