Whisky guides

What is cask finishing for whisky?

What is cask finishing in whisky? We'll answer your questions here, from why whisky makers do it to what secondary maturation brings to the spirit.

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A brief history

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Reading time: 9 minutes

Tequila finishes, red wine finishes, amaro casks, shochu casks. Not a week goes by without a big cask finish release from Scotland, Ireland, and beyond. Cask finishing is such a big part of whisky these days, that it’s hard to imagine that it’s actually a relatively recent technique.

A brief history of cask finishing

Cask finishing, maturing a whisky largely in one type of cask, usually bourbon, and then finishing it another, often sherry, was pioneered by David C. Stewart MBE at William Grant & Sons in the 1970s. Stewart, who was master blender from 1974 until 2023, experimented with the technique resulting in the launch of Balvenie DoubleWood in 1993.

Why is whisky finished in sherry casks? Placing whisky in barrels that used to hold sherry is a time-honoured technique that dates back to when sherry was imported regularly into the UK in the 19th century, while the colour and flavour it adds (fruity, nutty, and spicy notes) are prized by whisky makers. Oloroso is most common, but other varieites like amontillado, fino, manzanilla, moscatel, palo cortado and Pedro Ximénez are also used.

But was Stewart the first? In 1987 Glenmorangie released a 1963 vintage single malt which was finished in oloroso sherry casks. This was followed in the early ’90s by a Glenmorangie Port cask-finished whisky and then a plethora of other cask finishes like Madeira, sherry and Sauternes.

In fact, cask finishing is a technique taken from Cognac where older brandies would be perked up by ageing them for a period in a newer cask, i.e. one with lots of wood influence, before bottling. I tasted an 1885 Hermitage Cognac a couple of years ago that had been aged using this method and it tasted young and vibrant.

David C. Stewart MBE nosing a whisky in The Balvenie's warehouse

David C. Stewart MBE is regarded as a pioneer of cask finishing

What are cask finished malts? The influence of wood

Casks aren’t airtight so can ‘breathe’ – oxygen enters the barrel through the wood and water can evaporate out. This process draws the liquid (whatever that might be: sherry, red wine, Port etc.) inside a barrel into the wood. When a producer empties that cask, the liquid drawn into the oak stays there.

Refill it, and when the ‘breathing’ process starts again, that new liquid is drawn in and will be influenced by the first liquid still held in the wood. That’s why spirits can take on some of the character of whatever was in the barrel previously. Once emptied, casks need to be reused quickly or they can dry out and develop bacterial infections which can spoil whatever is put in them next.

Cask finishing can be used to enliven an older spirit. With very old releases from distilleries, the master blender will often put the spirit for a year or two in a first-fill (one that hasn’t had whisky in it before) sherry cask to add sweetness and body. Cask finishing can also be used to add interest to young spirits, adding a layer of complexity that couldn’t be achieved by simply ageing in a single type of cask. Some brands such as Darkness use a smaller cask such as an octave (50 litres) for the finishing process meaning more wood contact (due to a greater surface area to volume ratio) and therefore cask influence.

There's a huge variety of casks out there just waiting to have whisky filled into them

Brand synergy

As well as flavour, cask finishing can be a boon to marketers. Having an exciting other spirit or wine to shout about makes a change from just telling the same old story about the distillery, and the packaging team can really go to town. Witness the cherry blossom bonanza of the recent Glenfiddich Grand Yozakura 29 Year Old which is finished in Japanese awamori casks.

Furthermore, cask finishing can create what‘s known in the business as ‘brand synergy’ – putting two great brands together so both shine the spotlight on the other. Perhaps the most successful example of this is the Green Spot Léoville Barton release, where this famous Irish whiskey is aged in casks that previously held wine from the legendary Irish-owned Bordeaux chateau.

But also wine cask finishes can make a virtue of a necessity. Bourbon casks are heavily in demand from the burgeoning world whisky industry while sherry casks, on the whole, have to be specially created by seasoning European or American oak barrels with sherry. In contrast, the wine business is awash with used casks that can be picked up very cheaply. This is because many wine producers want some oak character in their wines so will only use casks two or three times before selling them on.

A bottle of Glenfiddich Grand Yozakura 29 Year Old

The cherry blossom bonanza that is Glenfiddich Grand Yozakura 29 Year Old

Rules for cask finishing

Different countries have different rules for which casks can and can’t be used. In 2019 the SWA (Scotch Whisky Association) relaxed its regulations to allow ageing in a wider variety of casks including ones that previously held Tequila and mezcal. This has proved popular with marketing departments if not with whisky lovers. Since then we’ve seen a deluge of increasingly outlandish finishes including agave spirits, Japanese spirits, and more.

No matter what they held, Scotch whisky casks must be made of oak. In other countries such as Ireland and England, however, producers are allowed to use a variety of wood such as chestnut and acacia – leading to more variety in cask finishing.

Can bourbon have cask finishes? Yes, although historically they weren't common. The temperature in places like Kentucky means that cask extraction is accelerated and it's easy to overwhelm the spirit, so they're trickier to manage than in Scotland or Ireland. The bourbon industry is increasingly embracing cask finishes, however, with brands like Angel's Envy using a Port cask finish. As long as the primary aging occurs in new, charred oak barrels, and your secondary barrel isn't a used bourbon barrel, then you've got flexibility.

And finally, how long does a whisky have to be in a cask to qualify as finishing? You might be surprised to learn that there are no rules here. It could be weeks, months, or years, but at the same time technically it could just be minutes – though this would be a little pointless.

Some cask finishes are very subtle, some not so. Some add something to the whisky, whereas others, and I’m thinking of some agave finishes that I have tasted, taste like a dog’s dinner. As always, however, it’s up to your taste buds to decide.