Several specialty craft beers and extreme barrel-aged imperial stouts reach an alcohol by volume of 14 percent, pushing the absolute boundaries of traditional fermentation. Master brewers achieve this high alcohol content by utilizing specialized high-tolerance brewing yeasts, prolonged fermentation cycles, and extensive aging in bourbon, whiskey, or wine casks. Because of their immense alcoholic strength and rich, complex flavor profiles, these potent brews are typically packaged in small bottles and savored slowly like fine wines.