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The angel’s share: evaporation from the cask

Discover why a whisky cask slowly empties during maturation, how climate and storage influence evaporation, and why loss is part of flavour development.

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  • Water and alcohol evaporate through oak
  • Scottish casks lose roughly 2% of volume per year
  • Climate and storage affect which component leaves faster

Where does the whisky go?

An oak cask is robust but not perfectly airtight. During maturation, small amounts of water and alcohol move through wood and joints into the surrounding air. This annual loss is poetically known as the angel’s share.

The Scotch Whisky Association uses roughly 2% volume loss per year as a broad guide for a Scottish cask. The real path is neither linear nor identical: cask size, wood, age, fill level and warehouse conditions all matter.

  • Water and alcohol evaporate through oak
  • Scottish casks lose roughly 2% of volume per year
  • Climate and storage affect which component leaves faster

Climate, warehouse and strength

Temperature and humidity influence evaporation. In a cool, humid Scottish warehouse alcohol may decline relatively strongly; in warmer or drier conditions water may leave faster and alcoholic strength can develop differently.

Position within a warehouse matters too. Airflow, temperature cycles and storage style create distinct microclimates, so two equally filled casks can finish with different volumes and ABV after years.

More loss is not automatically better

Evaporation concentrates some compounds while wood, oxygen and time continue to shape aroma. Less liquid does not guarantee quality: a cask may become elegant, overly woody or fall below the required bottling strength.

Read age, current ABV, cask type and yield together. Use the cask, age and strength guides to understand why an old bottling may cost more without treating age as a flavour score.

Transparency

Sources, image makers, licences and methodology are brought together here. Wherever possible, Whisk(e)y Compare links bottle data and distillery status to producers, trade bodies and other primary sources. Scores describe flavour intensity, not quality.

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Frequently asked questions

Clear answers

Does exactly 2% evaporate every year?

No. Two percent is a common Scottish guide; real loss varies by cask, year, warehouse and climate.

Does only alcohol evaporate?

No. Both alcohol and water leave. Their relative rates determine whether ABV falls, rises or stays comparatively stable.

Can a cask become too weak for Scotch?

Yes. Scotch must be at least 40% ABV when bottled, so long maturation requires monitoring volume and strength.

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