Why oak barrels make the best wine

The relationship between wine and oak goes back centuries. Originally chosen simply because it is watertight and easy to work, the effects that it has on wine have become increasingly appreciated, especially in high-quality and high-priced wines.

The aromas and flavours that oak imparts - of toast, coffee, caramel, toffee and vanilla - depend on the type of barrel used, how old it is and how long the wine remains in it.

Oak barrels are toasted, or fired, on the insides. The level of toasting and the way it is done will alter the flavour of the wine. A light toast will impart toasted bread, resin and wood. A high toast will give roast coffee or caramel. Barrel-makers, tonneliers, use either traditional fires, blowtorches or ovens to toast the wood and each method has subtly different effects on the wine.

The choice of the wood is also important. France has forests dedicated to the production of oak for barrels which are desired above all others, but Eastern European oak is now also used. American oak, is cheaper than French and, coming from a different species, has a different character. American oak is regarded as preserving the fruitiness of wines and giving more vanilla flavours. It is very popular in the production of Rioja.

Finally barrels come in several sizes. The common Bordeaux barrel holds 225lt, but 500lt and 600lt barrels are increasingly popular, especially for southern French wines.

All these flavour differences are only really noticeable when the barrel is first used. In subsequent years the oakiness diminishes until after three or four years little flavour is imparted.

However, flavour isn't the only reason for using barrels. Oak is porous and the barrels need to be regularly topped up, meaning that the wine gently oxidises over time. This oxygenation, combined with the extraction of oak tannins, helps smooth out the texture of red wine and bind the colour without removing the preservative qualities of the tannins. Hence barrel-ageing is the preferred method for making great, age-worthy wines from Cabernet Sauvignon, Merlot and Syrah.

Alternatively, in Burgundy, the barrels help bind the fragile colour of Pinot noir and add structure and body to the wine. White wine, notably Chardonnay, is often fermented in barrels as well as aged in them, giving a buttered toast richness and glossy texture. Oak tannins also help to clarify wines by removing the hazy grape proteins.

At first, the wine extracts a lot of flavour from the barrel but experiences little oxidation. Leaving the wine in-barrel extracts more oak flavours as well as oxidising the tannins. So the winemaker has to decide how long to keep a particular wine in barrel. In some regions, this has been written into the rules of the appellation. In Spain, and Italy to a lesser extent, length of time in oak is used to differentiate wines into quality brackets such as Crianza, Reserva and Gran Reserva.

The advantages of oak and especially the association of oaky aromas with high-quality wine, has encouraged wineries to look for alternatives to the costly and laborious barrels. A new French barrel costs €750 before taxes. Adding toasted oak chips or powder to large stainless-steel tanks of wine gives the impression of oak-ageing. Micro-oxygenation machines which bubble controlled doses of air in to the tanks try to emulate the porous barrels. Today, vast amounts of smooth, oaky-tasting wines are made without ever having touched an expensive barrel.

Often results are clumsy and obvious but the recent development of staves and cubes of high-quality toasted oak by the major tonnelleries have offered the ability to create wines which closely resemble barrel-aged wines at a significantly lower cost. Whether the choice is barrels or oak alternatives, the quality of the resulting wine will be down to the quality of the grapes and the skills of the winemaker.

Jonathan Hesford is the owner, vigneron and winemaker of Domaine Treloar in the Roussillon. www.domainetreloar.com