Angels' Share

The volume of spirit lost to evaporation through the oak during maturation, reckoned at roughly two per cent a year in Scotland.

Oak breathes, and what escapes through it is the angels’ share. In Scotland the figure is conventionally two per cent a year, which sounds modest until you compound it: an eighteen-year-old malt has lost roughly a third of what went into the cask, and a thirty-year-old well over half. That is the real reason old whisky costs what it does. Climate decides the rate, and it decides the direction too. Scotland’s warehouses are cool and damp, so alcohol evaporates faster than water and the strength falls as the years pass — which is why a cask must be watched, since Scotch dropping below 40 per cent is no longer legally Scotch. In Kentucky the loss runs nearer four per cent, and in the heat of Goa or Bangalore it can reach ten or twelve, with water leaving faster than alcohol so the spirit grows stronger as it shrinks. There is also a ledger behind the poetry. Whisky matures in bonded warehouses under the eye of the Revenue, and duty is charged on what comes out rather than what went in, so the angels’ share is the one quantity in the trade that evaporates untaxed. The name is a distiller’s joke about an accounting allowance.