ost whiskeys are aged in wooden barrels. The wood (often oak) absorbs sulfur compounds from the liquid inside while imbuing it with unique flavors and aromas. However, wood is porous, and over time some of the whiskey inside will evaporate. Around 2% of the total liquid inside a barrel is lost each year, which can mean major losses for long-aged whiskeys (a 15-year whiskey will have lost at least 30% of its original volume by the time its barrel is corked). The evaporated whiskey is known as the “angels’ share,” since the missing liquid presumably evaporates to the heavens.