The story
For most of history, wooden barrels were simply the way beer was stored and transported. Brewers generally tried to prevent the wood from flavouring the beer, often lining casks with pitch. Stainless steel and aluminium eventually replaced wood, and the barrel faded from the brewery.
Then craft brewers rediscovered it on purpose. In 1992 Goose Island brewmaster Greg Hall aged a strong stout in used bourbon barrels, creating what became Bourbon County Brand Stout. It is widely regarded as a landmark in modern barrel aging. Since then, brewers have filled barrels that once held bourbon, rye, wine, rum, tequila and more, turning barrel-aged beer into one of the most exciting and collectible categories in beer.
What it tastes like
Barrel-aged beer depends heavily on the base beer and the barrel’s previous occupant. Bourbon-barrel stouts are often rich, dark and syrupy, with vanilla, caramel, coconut and toasted oak layered over chocolate and coffee. Wine-barrel beers can show tannin, dried fruit and vinous notes, sometimes with a sour edge. The alcohol is usually high, the body full, and the flavours intense. These beers are made for slow sipping.
How it’s made
Brewers start with a strong base beer, such as an imperial stout, barleywine or sour ale. It is transferred into used barrels, where it may rest for months or even years. During that time the beer absorbs flavours from the wood and from any residual spirit or wine soaked into the staves. Temperature swings push beer into and out of the wood, deepening the character. Some beer evaporates along the way. Brewers often blend barrels to achieve a balanced final product.
Fun fact
Bourbon, by US law, must be aged in new charred oak containers. That means distilleries cannot reuse their barrels for bourbon, so a steady supply of freshly emptied bourbon barrels is available — a happy accident that helped fuel the barrel-aged beer boom.