Free The Drunken Botanist: The Plants that Create the World's Great Drinks by Amy Stewart Page B

million years. They emerged as a distinct genus not long after the mass extinction of dinosaurs. Taxonomists disagree about the exact number of species; depending you who you ask, the number ranges from sixty-seven to six hundred. However, we are only concerned with the handful of American, European, and Japanese species used by barrel makers for wine and spirits.

    Wooden barrels have been in use for at least four thousand years, judging from archeological evidence, and oak was probably the natural choice from the beginning. The wood is hard, dense, but still pliable enough to bend into a slight curve. It was used for shipbuilding, and surely one of the first pieces of cargo to be loaded on the ship was a barrel of wine for the crew.
    What the first barrel maker might not have known was that the anatomy of oak is perfectly designed not just to hold but also to flavor the liquid it contains. Oak trees are “ring porous,” which means that the vessels that carry water up the tree are found in the outer growth ring. As the tree matures, the older vessels become plugged with crystalline structures called tyloses, and as a result, the center of the tree—the heartwood—doesn’t conduct water at all, making it well suited for use as a watertight barrel. American oaks are particularly rich in tylose as compared to European oaks. In fact, the European trees have to be carefully split along the grain, rather than cut, in order to avoid rupturing vessels and creating a leaky barrel.
    The trees also happen to produce an astonishing array of flavor compounds that break free from the wood in the presence of alcohol. European oak, Quercus robur in particular, is high in tannins, which give wine a certain roundness and full-bodied quality. American white oak, on the other hand, releases the same flavor molecules found in vanilla, coconut, peach, apricot, and cloves. (In fact, artificial vanilla is made from a sawdust derivative because it has such high levels of vanillin.) Those sweet flavors might not be what a winemaker is looking for, but they are pure magic in bourbon.
    Perhaps the most important influence on oak-aged spirits comes not from the tree but from the barrel makers, called coopers. They learned that coaxing oak staves into gentle curves required two things: time and heat. Freshly cut oak is given time to dry, which not only makes it easier to work with but also concentrates those important flavors. The staves are also lightly cooked to make them more pliable as they are shaped, and fire causes some of those flavors to caramelize, so that caramel, butterscotch, almond, toast, and warm, woodsy, smoke essences emerge.
    Some whiskey barrels are entirely burned inside. No one knows how this started. It’s possible that a cooper accidentally lit a bigger fire than intended and decided to use the barrel anyway. Perhaps thrifty distillers burned the inside of old barrels used to store salted fish or meat to eliminate the flavor before filling it with whiskey. Regardless, the layer of charcoal filters and flavors the whiskey, particularly as the wood expands and contracts with changes in the weather. The Lincoln County process, made popular by Jack Daniel’s, takes this one step further by burning sugar-maple wood and filtering the whiskey through ten feet of charcoal before it ever reaches the barrel.
    The coopers made one more contribution: after Prohibition, when it became necessary to enact new laws regulating the now-legal liquor industry, they helped ensure that bourbon (and other whiskey) would, as of July 1, 1936, have to be stored in charred new oak containers in order to claim the name. This, the newly formed Federal Alcohol Administration claimed, distinguished “American-style whiskey” from Canadian products, which possessed a milder flavor owing to the fact that they were distilled at a higher proof and stored in reused cooperage. Although the law has gone through some revisions and