At that point, the whiskey is somewhere between 55% and 65% ethanol, water making up most the rest. Most whiskey makers will add more water to bring the ethanol concentration down to 40%—80 proof in liquor lingo. Water and ethanol are close enough chemically that they mix together completely—you’ll never find an old bottle of whiskey that’s separated into alcohol and water layers. But they’re not identical, and advanced imaging technology has shown that water and ethanol molecules tend to cluster unevenly within the mixture. Those oily halves are mostly found at the surface, with as little contact with water molecules as possible.

Source: Forbes August 18, 2017 23:26 UTC