The whisky is left a minimum of three years but usually between 8 and 25 years in wooden barrels to mature. The bonded warehouses are cool and earth-floored to provide an even temperature and humidity. The barrels lose about 2% alcohol per annum - the so-called 'angel's share'. It is worth noting the investment tied up in each one of these modest low stone warehouses - each full-size cask can contain up to 110 gallons - easily &163;15-20,000 of spirit once it reaches the shops.