" Angels’ Share: In storage, a small amount of alcohol escapes the barrel through evaporation. Distillers call this lost alcohol the angels’ share. Whiskey and brandy makers estimate that the angels get about 2 percent of the alcohol in a barrel each year, although that can vary depending on humidity and temperature. Fortunately, they can afford to lose some, as most spirits are aged at a higher proof than the final bottling. "

― Amy Stewart , The Drunken Botanist: The Plants That Create the World's Great Drinks