Distillers Have Rediscovered an Age-Old Secret to Unlocking Whiskey Flavor

The liquor industry is obsessed with the strength of a whiskey when it’s bottled: 80 proof, 100 proof, cask strength. But there’s another measure of alcohol potency that’s just as important—if not more—barrel entry proof.

While the proof stated on a label is for the finished product, barrel entry proof is the alcohol level of the spirit when it goes into a barrel before it starts aging. While this sounds like a bureaucratic footnote, it’s actually incredibly important for how the alcohol...