There are two uses of oak in the field of wine, one is the cork which is used as a stopper and harvested from the bark of the Quercus suber every nine years. The other is the oak used to make wine barrels.
The great French oak forests such as Nevers, Limousin and Tronçais were first used by Napoleon for ship building purposes. Although very good for making ships, English oak is too dense for making wine barrels. The oak from warmer climates better allows the wines to breathe in the barrels.
Barrels made by coopers are used for the storage and maturation of wine, beers, whisky and vinegars. The wood can affect the flavour of wine and adds tannins. If the wine can breathe this softens and develops the flavours.
In Bordeaux the size of the barrel is 220 litres which gives a large surface area of wine in contact with the wood. Only the best and most expensive Chateaux can afford to use new oak each year. The used barrels will be sold on to lesser chateaux after two years.
French oak barrels are made by taking split wood which has been seasoned outdoors and then constructing the staves into a barrel over a fire. A metal hoop is then forced over the barrel which contracts when cool to hold the staves together and makes a watertight container.
In America, for wine and bourbon casks, the wood is not seasoned outside. It is kiln dried and sawn instead of being split. This gives softer tannins and a much more oaky vanilla taste to wine stored in them, such as Rioja. Many Scotch whisky distilleries will have barrels made that are given to Sherry producers to use for a few years. They then get them back to store whisky in giving the whisky its colour. Cognac aged by the docks in London ( a cool damp area ) takes on less colour from the wood hence the term very superior old pale .
In Cognac the spirit is aged in Limousin oak. Poor soil in the Limousin forest results in wood that is at the far end of the scale in terms of looseness of grain. The release of flavours in such wood is too aggressive for wine , but makes it ideal for spirits. As it rests in the barrels there is an evaporation called ‘the Angels share,’ without this the spirit would be too harsh as it softens it.