angel's share, n.All

Angel's share accounts, on average, for about a 2% loss a year but it can be up to 12% a year in hotter climates.

Angel's share means 53 gallons of new-make Pappy becomes 13 gallons after 23 years in the barrel.

2% of whisky evaporates through the barrels each year; thus, a 20 year old cask of whisky contains only about 40% liquid

Whisky evaporates differently in different climates. In Scotland alcohol evaporates more leaving a lower ABV product while in Tennessee water evaporates more causing the ABV to increase.

Angel's share is to thank for the mellow taste of whisky, the result of the inhaling and the exhaling of the whisky through semi-permeable membrane of the wood

Angel's share is very likely just a myth made up by clever distillery employees so they can keep surreptitiously taking a wee dram from casks during their shift