Up until the mid-18th century, European brewers aged their beers in oak barrels, but they abandoned the technique during the Industrial Revolution when metal vats became the new standard vessel for fermentation. More than two centuries later, U.S. craft breweries resuscitated the practice. Today, those breweries are making more varieties of beer using oak barrels than their European counterparts ever did, and they’re doing so with a truly American sense of exploration. From those exploratory efforts have come …