Oak casks and barrels breathe, which is why some of their content evaporates during maturation

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The percentage of liquid that evaporates annually from a cask is called the angels’ share. This number may vary depending on the location of the warehouse, so in Scotland, for example, one might see an evaporation percentage between 1.5 per cent and 2.5 per cent per year, while in hotter climates, like India, it may be as high as 12 per cent.

During maturation in Scotland the percentage of alcohol slowly decreases because more alcohol than water evaporates with the angels’ share due to the relatively mild climate, the humidity level, and the relatively small changes in temperature between summer and winter.

This is an edited feature provided by SMWS ambassador Hans Offringa from his comprehensive A Field Guide to Whisky: An expert compendium to take your passion and knowledge to the next level which you can purchase by clicking on the link.