What type of wood do they use?
The most typical barrel used for aging is American oak, which imparts flavor much faster than its French oak counterpart. Innis & Gunn has experimented with everything from Irish whiskey-infused oak (for the Irish Whiskey Cask Stout), to Canadian Black Cherrywood.
Jester King primarily uses oak from a range of sources (mezcal barrels for Encendía farmhouse ale, Old Tom gin barrels for Viking Metal), but have also experimented with sherry barrels and cedar spirals. Other breweries, like Russian River, experiment with wine barrels ranging from Chardonnay to Pinot Noir.