Whisky Magazine Issue 112
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We investigate the influence of different casks sizes when maturing malt whisky
Malt whisky is generally aged using three different sizes of cask. These includes barrels previously used to age Bourbon, with a capacity of around 200 litres; and two types of casks previously used to age sherry, which are hogsheads with a 250 litre capacity and butts at 500 litres. As malt whisky develops up to 70 per cent of its flavour during aging, every aspect that influences this process, including cask size, is a significant factor.
How influential the cask size can be on the maturing spirit is based on a straightforward formula: the volume of liquid in the cask in relation to the surface area of the cask. The smaller the cask the greater the amount of liquid (proportionately) is in contact with the oak surface, and it's from here that the spirit extracts various flavour compounds during the aging process.
Consequently, the smaller the volume of liquid in the cask, the greater the concentration and impact of the flavours which are extracted from the oak. Correspondingly, the larger the volume of liquid the more ‘diluted' the extracted flavours.
The range of flavours extracted depends on the type of cask. Bourbon barrels, for example, contribute vanilla, honey, and various fruit flavours, with a light, dry sweetness. Sherry casks add a richer sweetness with dried fruit notes including raisins. These flavour differences are principally due to the species of oak, with Bourbon barrels made from American oak (Quercus alba) while Sherry casks are European oak (Quercus ...