Whisky Casks: the Different Types, Why They Matter and How They Influence a Whisky
Have you ever really thought about what you’re experiencing when you take a sip of your favourite dram? Sure, we all love the earthy, saltiness of a classic peat, or marvel at how a smoky morsel can change on the palate.
But there’s more to it than that. Every drop of your favourite whisky is alive with tradition. The past is present in every perfect pour. Centuries of innovation, invention and ingenuity go into creating those malts moments that nobody else could ever master.
All of this - whether it’s sticking to the tried-and-tested or experimenting with new horizons of luxury - wouldn’t be possible with one key factor in the whisky making process - the casks.
Ready to bask in the genius of the casks? Let’s take a deeper look at the importance of whisky casks, as we speak to Craig Wallace, a master blender and pioneer of liquid creation who reveals exclusive insight into some of the innovations he’s overseen across many of Scotland’s leading distilleries.
How are casks used in the whisky making process?
In short, whisky as we know it wouldn't be the same without casks. Every cask leaves a unique and essential mark on the spirits they help produce. This is known as the maturation process in whisky making.
Casks aren’t just passive, practical vessels. They actively shape the soul and character of our favourite spirits. Through extraction, oxidation, and concentration, the spirit absorbs compounds from the wood, mellowing and evolving into the final product that has kept many distilleries open and in business for hundreds of years.
The ‘filling plan’ of a cask refers to the practice of refilling casks for maturation. When a whisky has first-fill casks, as the name suggests, it means it’s the first time the cask has ever been used. These typically imbibe stronger and more pronounced flavours. In the trade, these are often called more ‘active’ casks.
Craig explains...
"Casks are absolutely critical in the production of Scotch not only from a regulation perspective, but from a flavour perspective. We put many measures in place to assess the quality of casks from traditional methods like checks from time served coopers to modern technology such as tint meters. We can measure the colour of every cask that is disgorged and decide on the next steps in terms of cask filling or re-coopering.
We also have industry leading analysis to lean on to back up all of our sensory checks on the whisky. Casks should not be assessed in terms of age being the only measure of quality, wood activity is most critical as we need both char to remove immature flavours and toasted active wood beneath to add flavour to the whisky from the wood."
What are the most common types of whisky casks?
There are many different types of cask that can be used, but there are some that are relied on for the traditional and sought after flavours they help awaken in a liquid.
Bourbon casks
A widely used barrel, American Oak bourbon casks are typically rich in vanillin, lactones, eugenol and fruity esters that help a whisky develop sweet, spicy, nutty or fruity flavours.
Sherry casks
Sherry casks are another popular and oft used barrel, and the flavour they bring to a whisky is dependent on the type of sherry it was used for. Because sherries can range from the super sweet to the drier flavours, different sherry casks and their flavour profiles include:
Oloroso sherry can add nutty, spicy, dark fruits and leathery notes
Moscatel sherry casks can flavour a whisky with floral and honey notes, as well as hints of tropical fruits
Pedro Ximenez sherry casks bring the sweetness of raisins, treacle and chocolate
Fino sherry casks offer dry, citrus notes.
Craig shares with us, ‘‘For Scotch, all casks are made of oak, mainly sourced from USA, France, and Spain.’
‘We do source casks from other countries as we experiment (always oak species) and these will be released for special bottlings in the future.’
As for how casks impact the flavour, how does someone who works with whisky production in his daily life view it?
Craig shared, “Historically we would have targeted ex-sherry casks to malts as they would overwhelm a grain whisky. Therefore American oak (ex bourbon) is used for grain whisky mainly as the vanilla notes complement the delicate grain whisky.”
“Refill casks are also very important as they are less ‘active’ but still deliver a gentle maturation that allows distillery flavour to shine. This is so important for quality whiskies.”
“Rejuvenated casks are made when a refill reaches the end of its active life. We scrape a small layer of wood from the cask and char it again. This gives a fantastic layer of freshly toasted oak beneath the fresh char, and allows for the essential spiciness one might expect from the likes of Johnnie Walker Double Black and Talisker Storm.”
Is just one type of cask used per whisky?
How many casks are involved in producing a single spirit depends on the type of whisky. Single cask or single barrel whiskies will just use liquids matured in one cask. This is often intentionally done to spotlight the unique character of a type of cask.
However, many whiskies will use a combination to create a distinct and complex flavour profile. This is how we achieve whiskies that take our palates on a flavour journey with each sip. Notes of fruit can suddenly open up with a hint of spiciness, or darker whiskies might have just that perfect flash of softening vanilla.
It’s down to the casks that whisky continues to be an exploration of flavour, a discovery of decadence.
Casks are absolutely critical in the production of Scotch not only from a regulation perspective, but from a flavour perspective.
-Craig Wallace, Master Blender
The final word from Craig
We had to ask Craig before we let him back to what he does best - which is help produce some of the finest drams coming out of Scotland - what are some of the more unusual innovations or processes he’s overseen with whisky casks? And we weren’t disappointed - we found out one of his own products oversaw an industry first.
He revealed, “Diageo was the leader in the changes to Scotch Whisky Association (SWA) casks regulations in 2019. Buchanan’s Two Souls was the first ever Scotch whisky matured in an ex-tequila cask - (using the deluxe Don Julio tequila - because who would settle for less?) after the regulations changed. This was my product and was followed up with Lagavulin’s Mezcal finish and tequila finished festival bottlings. Lagavulin also did a very interesting cask series experimenting with Guinness casks.”
“Over my many years as a Master Blender I have assessed tens of thousands of cask samples. Age is definitely a misleading measure on quality. Some 30 year old whiskies have been very disappointing - either too woody or not active enough to deliver any real flavour shift.”
“When I assess quality whisky aged between three and ten years, I can see that the active casks are super interesting and can deliver flavours people would not expect, with an amazing interaction of distillery and wood that can be selected for flavour balance rather than relying on age as the main selling point.”
Interested in finding out more about what takes place at the distilleries and the whisky making process? Why not consider booking a distillery tour where you can see it all come to life for yourself.
Explore the world of Malts
You might be loyal to an old favourite, but there’s plenty of niche whisky brands that deserve a place in your home bar too. Discover a new dram with us.
Deciphering a whisky bottle can, at times, feel complex - but it's worth it. You can learn a lot from a bottle before you’ve even had a sip, especially if you know what to look for.
Curious about Japanese whisky? What does it taste like, and what makes it different? Find out that and more with our expert guide.