Illustration by Alyssa Nassner
The selling and marketing of whiskey sometimes includes the phrase “cask strength.” These words are placed on select bottles to make them stand out to consumers ordering drinks at bars or shopping at brick-and-mortar or online stores.
As legal definitions vary (or simply don’t exist), putting the words “cask strength” on a bottle can be a superficial designation. In many cases, it signifies exclusivity, or some sort of direct access to a barrel-strewn whiskey tasting club. However, it can also refer to a spirit bottled directly from the barrel in which it was aged, with no water added to adjust the proof—something also commonly called “barrel proof” or “barrel strength.”
“I think most distillers would agree that a cask-strength whiskey is where the alcohol by volume of the finished, bottled product is the exact same as the abv of the liquid of the casks that they were sourced from,” says Matthew Hofmann, managing director and cofounder of Westland Distillery. “Or even more simply, it’s undiluted whiskey.”
Key factors that affect whiskey’s strength, or alcohol by volume (abv), and flavor within its cask: the type of barrel used, such as new oak versus an older barrel, and the type of wood the barrel is made out of, like American, European or Japanese oak (Mizunara). These factors affect how a particular wood reacts with, and to, the alcohol inside.
Spending time in contact with wood also contributes aromas, flavors and a slight amber hue to a spirit. The charred wood inside the barrel absorbs rough notes left over from distillation, much like a Brita filter does with tap water. And since wood is permeable, whiskey can absorb oxygen, as well as adapt to shifts in temperature and metamorphize from a clear liquor to the familiar brown spirit most of us know as whiskey.
Most whiskeys are diluted slightly and sold at 40–45% abv (80–90 proof). Cask-strength whiskey is usually bottled at 50% abv (100 proof) or higher.