WHY USE AGED CASKS?
With Scotch whisky, it is important that the cask has had a previous life. This is in stark contrast to Bourbon Whiskey, in which only new, or ‘virgin’ oak casks may be used. However, Scotch is traditionally matured for much longer than bourbon. And a virgin oak cask would overpower many of the more subtle flavours. 90% of Scotch Whisky casks are ex-bourbon casks, where the sweet bourbon whisky has soften the wood. And the Spanish sherry butts are among the most desirable. A proportion of the previous contents of a cask will have been absorbed into the wood. Which would season it with its own unique flavour.
Casks are often re-charred. The inside of the cask is essentially set on fire, leaving a thin layer of charcoal. This is done for the purpose of re-activating the natural sugars, within the wood which gives it a new lease of life.
Once filled with new make spirit, whisky casks must age for a minimum of three years on Scottish soil before they can be called Scotch. Maturation is essentially an extended interaction with the wood of the cask. As temperatures fluctuate the spirit is drawn in and out of the inside surface of the oak. This, the charring, and the previous contents slowly colour and flavour the spirit. By the time the whisky reaches a rich amber colour, it takes on significant flavour and complexity.