Wood has chemical compounds responsible for various aromas and flavours we experience in the wineglass. Sweet, vanilla tones or smoky, peppery notes are derived mainly from the oak barrel. Certain cultivars contribute spicy, peppery characters to wine, but overall the secondary characteristics of a wine emanate from contact with wood.
The difference in barrels is a result of different types of oak, French, American or even Hungarian. Quercus Alba originates in the USA, while most of the oak forests in France are of the Quercus Sessile or Quercus Pedunculate species. American oak is more liquid tight due to its anatomical structure and therefore staves can be sawn, whilst French oak is traditionally split.
The next big difference is in how the oak is seasoned and prepared for use in the wine industry. French oak is traditionally seasoned outdoors for up to 3 years, encouraging green tannins to leach out. The other alternative is to artificially season the oak by placing it in ovens to dry out, however those green tannins are not always conclusively removed from the oak and can show in the final product – wine.
Finally, the toasting of barrels leads to the formation of aromatic compounds which are important for maturation, aromas, flavours and mouthfeel of the wine. Barrels are graded in four categories: Light toasting (LT), Medium toasting (MT), Medium + toasting (MT+) and Heavy toasting (HT). The selection of barrel is thus critical in determing the style and complexity of a wine and much care is taken when selecting the right barrel. Winemakers are therefore specific in terms of what they order – from forest, to seasoning, toasting level and cooperage and thus the choice of barrel becomes the winemakers signature.