The use of oak barrels in the wine industry initially came about as a consequence of transportation. Before this, wine was transported in animal skins. Somewhere along the way, it was discovered that storing the wine in oak actively improved it, giving it added complexity. Centuries later, the science behind oak and wine has become an essential element in winemaking. Nowadays one doesn’t simply talk about “oak,” but about its provenance, its type, its toasting levels and even the cooperage from which the barrel has come! New oak barrels are expensive, so in the past decade, various alternatives have been developed, including oak staves and oak chips.

Provenance and Origin

France is the primary source of oak barrels and is considered to produce those of the best quality. Other sources include the Baltic states and Eastern European countries, as well as Portugal. When selecting oak for a barrel, the cooper considers not only the origins of the oak but also whether it is tightly or loosely grained. The tightly grained types, less porous, are considered the best for wine ageing as they are more watertight and less likely to leak. The flavours coming from the tightly grained oak also give a more elegant taste to the wine.

The main French forests that supply wood suitable for barrel making are in Vosges, Limousin, Nièvre and Allier. Certain forests, such as Tronçais in the central region, are particularly well known. Though it may not sound particularly important, the provenance of the oak is highly significant because the climate affects the grain size, which is of great importance. Another factor affecting the size of the grain is the spacing between the planted oaks. In a wild forest the trees grow far apart and can be loose-grained, but in a planted forest the trees are planted tightly together. Consequently, they must dedicate all their energy towards becoming tall to gain access to the sunlight. Hence the wood grain becomes tight.

French oak is considered the best and is certainly the most expensive, costing around €600-€700 for a new barrel. However, American oak is also widely used, with particularly good results in Spain and Australia. American winemakers tend to use mostly French oak for their top wines. Stylistically the American oak is richer in tannin and offers exotic coconut and vanilla aromas.

Cooperage

Once the staves have been formed, either by splitting or by saw, there is still a long process ahead before the barrel is finished. Firstly, the wood must be dried. This can be done in the open, exposed to the elements and the different seasons (which is why it is known as “seasoning”). It can also be done inside using fans. This method is far quicker, but the results are not as good as traditional seasoning. Once the staves are dry, they are reassembled and  prepared for toasting. The level of toasting can be light, medium or strong. Light toasting is done for white wines while medium to strong toasting is reserved for red wines.

Balance

The size of the container also influences the wine in different ways. A small barrel will provide a greater ratio between surface area and volume of wine, and the flavours will be more pronounced than in wine matured in a large barrel. The standard size is 225 litres, but many producers are experimenting with other sizes to optimise the level of oak aromas in the wine.

The balance of oak aromas and flavours in wine is very important. A few years ago, there was a move towards excessive oak ageing, but lately, most winemakers have returned to a more balanced approach. Oak is merely a complement to a good wine and should not be its primary flavour. Depending on the concentration and style of a wine, a producer may choose to use only new oak, which gives full on toasty oak flavours, or perhaps 50% new and 50% one-year-old to soften the impact. In extreme cases, which luckily are not common, a producer may choose to use what is known as 200% new oak. Here, the wine is aged for around six months in new barrels, before being transferred into another set of brand new barrels, to maximise the oak expression.

Alternatives

Given the high cost of oak barrels, numerous less expensive alternatives have been developed. These include, for example, putting oak chips and staves into a stainless steel tank during the fermentation and maturation. This is a far less expensive way of bringing oak flavour to a wine and is suitable for mid-range quality levels.