Oak and Its Qualities

Though chestnut and cedar have been used in Europe and redwood in the United States, most barrels for aging wines and spirits are made from oak. Oak heartwood, the older inner wood, is a mass of dead cells that supports the outer living layers. The heartwood cells are filled with compounds that deter boring insects. These are mainly tannins, but they include such aromatic compounds as clove-like eugenol, vanilla-like vanillin, and oaky “oak lactones,” relatives of the characteristic aromatics of coconut and peach. From 90 to 95% of the heartwood solids are cell-wall molecules, cellulose, hemicellulose, and lignin. These are mostly insoluble, but the lignins can be partly broken down and extracted by strong alcohol, and all can be transformed into new aromatic molecules when the wood is heated during barrel making.