The containers that age whiskey, otherwise known as whiskey casks, are more than just a storage option for the liquor to be ready for consumption. Over the years, there have been many types of casks and processes used to treat whiskey, which help determine the final flavour of the liquor inside. The size and shape of a cask are significant factors that are taken into account while ageing – with smaller casks imparting a more concentrated flavour, making them more popular for finishing whiskies. Many distilleries also employ the use of casks that previously held other alcohols. For example, former bourbon casks are also used to mature whiskey and impart a sweeter vanilla and caramel note. Sherry casks are also popular for being diverse in profile and lending flavour to the final product.
The number of times a cask is employed to mature whiskey significantly affects the flavour of the dram. As a cask undergoes more refills, it imparts less flavour and colour. This would also be why you might observe many whiskies specify on the label whether the liquid was matured in a first-fill or refill cask. Wooden casks, especially oak, are the go-to wood for whiskey casks; each one going through a toasting process that caramelises the wood sugars to create sweet flavours infused into the dram. Some whiskies that mature in heavily charred casks, facilitates greater absorption of flavour in the spirit.
Sherry Cask
A popular fortified wine from Spain, sherry casks are frequently employed in maturing whiskies to bring out a fruity, nutty flavour with rich aftertastes. The oak wood cask imparts a rich flavour, while the sherry contributes to a velvety texture. Whiskies aged in sherry casks typically exhibit a darker colour with a subtle trace of sweetness from the previous alcohol.
Bourbon Cask
American bourbon is legally only allowed to be called bourbon if it is aged in new oak casks, meaning that there is always plenty to go around for the whiskey industry. When aged in these charred oak casks, the whisky acquires a spicy, smoky flavour from the wood and toasting process as well as a slight sweetness with hints of vanilla.
Rum Cask
The pride of the Caribbean, barrels used to store and age rum often find their way into the whiskey ageing process, imparting a robust flavour and a touch of sweetness to the cask wood. Whiskies aged in rum casks often exhibit a caramel flavour thanks to the residual sugars in the rum, which are rich and full-bodied, and usually designed to be enjoyed neat or with a few ice cubes.
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Tawny Port Cask
Another variation on the wine cask is Port – a wine from Portugal, is commonly used in maturing whiskies, providing a strong, woody flavour and an almost smoky taste. Whiskies aged in these casks are rich, full-bodied and drunk neat or with ice. While tasting a whisky from a tawny port cask, you might notice a slight sweetness attributed to the residual sugar in the cask.
Muscat Port Cask
Muscat port is a wine variety often used to mature whiskey as it imparts a strong, woody flavour reminiscent of a smoky taste. Whiskies aged in Muscat port casks are full-bodied, often enjoyed neat or with a few ice cubes.
Mizunara Oak
A speciality variation on the common oak casks come from Japan and are said to be highly sought after. The Mizunara oaks need to be a minimum of 200 years old before they are cut and shaped into casks – their huge demand resulting in them being some of the most expensive options available. Known for imparting flavours of sandalwood and coconut into the whiskey, the mizunara casks are in a league of their own.