From Seed to Stave
The making of an American oak barrel begins in the forest. Trees selected for barrels must meet stringent quality measures. Before the construction of a barrel begins, the wood is carefully sawn and seasoned – or aged – to soften the oak influence and improve flavor integration.
Trees and Forests
The American mixed temperate forests where white oak trees grow cover 53.8 million hectares, the largest contiguous forest in the world [ 1 ]. The most desired trees are from dense forests because they are forced to grow straight and tall with fewer limbs – leading to higher quality lumber for barrel staves. While there are many types of oak trees, the white oak (Quercus alba) – typically referred to in the beverage industry simply as American oak – is the most predominant species used for barrels.
The forests where American oak trees grow spans many states. Each state’s microclimates influence the characteristics of the oak, playing a significant role in flavor profiles. To produce wines with distinct styles, winemakers are increasingly requesting barrels from specific states.
- Oregon white oak (Quercus garryana)
- Most densely populated white oak (Querus alba) forests
- The extent of white oak (Querus alba) forests
Source: Wood, Whiskey & Wine, Henry B. Work.
From Tree to Barrel
It takes at least 80 years to grow an American white oak to maturity. The best trees have straight trunks, unblemished wood, and are free of low-hanging branches. The interior heartwood is used for staves and headers, with each tree producing two to four barrels. On average, one barrel is produced per acre per year.
American oak forest area has steadily increased since 1980, and is currently at pre-1947 levels. Regrowth is an important sustainability measure for both public and private land owners. In Missouri and West Virginia, there is 53-106 cubic feet of regrowth for every cubic meter felled. [ 2 ]
American white oak staves are quarter-sawn - cut against the grain - directly from log bolts. Allowing for nearly the entire log bolt to be made into watertight staves, American oak can be sawn given the trees’ high volume of tyloses, gum-like substances that plug the pores of the heartwood and prevent barrels from leaking. In contrast, the less-watertight nature of its European relatives, like French oak, compels coopers to split the wood along the grain, resulting in only 20 to 25 percent of the log bolt used for staves. [ 3 ]
Growing conditions, age and genetic variation of individual trees can strongly affect wood structure and composition. Even a stave’s original position on the standing tree trunk can influence its aroma composition. [ 4 ]
Staves are air-dried, or “seasoned,” for 24 months to achieve 12-14% moisture levels for liquid-tight barrels. Natural drying allows rain and other elements to reduce the tannins in the wood, softening the flavors. The seasoning process also results in pliable wood that can be molded into barrels without splintering.