Although the oak trees used to make barrels can grow for more than 100 years before they’re felled and sawed into planks, the wood is still not ready to hold spirit. Staves need more time and various applications of heat before they’re ready to be bent into shape.
Specifically, before it can become a barrel, wood will be seasoned, toasted, charred, or some mix of those treatments. And while there are plenty of confident claims from coopers and distillers about those methods, the scientific literature about these subjects is far behind. The research is catching up, however, and there is plenty of fascinating information becoming available to distillers today.