Production

Understanding the production of single-cask whisky

The road to a single-cask whisky is not as simple as it may seem
By Ian Wisniewski
We can’t help ourselves. Assessing and passing judgement is what we do, as whisky drinkers, which means not all drams are considered equal. Senior spirits, for instance, are typically placed higher in the hierarchy than junior counterparts. But one type of whisky which can transcend any prejudice – whether that be based on age, distillery or cask type – is a single-cask bottling: when a tiny batch of spirit from a single barrel has a solo, starring role, rather than being blended into a chorus line, as is the usual practice.

A single-cask bottling embodies far more meaning than the literal definition. “I describe these as snapshots in whisky history. There will never be an exact repeat of the experience. These are products at the pinnacle of whisky exploration. They have gravitas and rarity,” says Doug McIvor, reserve spirits manager at Berry Bros & Rudd.

A prime example is the Hedonism 10th Anniversary, a limited edition released in 2010 marking the decade since Compass Box’s founding by John Glaser. It’s also a singular example, being the only single-cask bottling from a single distillery released by the company in its now 21-year history. “We were looking at casks of Invergordon single grain, and one cask contained all the flavours we look for in Hedonism: vanilla, creme pâtissière, creaminess, coconut and gorgeous apple, so we decided to bottle this as a single cask. It is rare to find one cask that can do the work of several,” says James Saxon, whisky maker at Compass Box.

“No two casks produce the same spirit, so when whisky fans take their first sip, they know they are experiencing a bottle that is truly unique,” adds Sandy Hyslop, director of blending and inventory at Chivas Brothers. The word ‘unique’ is an evocative descriptor that naturally creates expectations of an individual, even idiosyncratic whisky that conveys the distillery character in a different manner. What exactly makes a cask sufficiently unique, and whether a line can be crossed into ‘too different’, is more difficult to say.

“It’s more of a gut feel than a list of characteristics to look out for. Sometimes we find an example that is too eccentric to be a single-cask bottling. We take a largely cautious approach,” explains Brian Kinsman, master blender at William Grant & Sons.

Uniqueness is also an interesting concept considering that production processes generally aim to minimise variability and promote consistency, to help blenders better plan for future releases. This principle applies as much to milling as it does mashing, fermentation or distillation, but coaxing natural materials such as oak – specifically, the core of oak tree trunks, the only part used to make casks for the Scotch whisky industry – into conformity can be more challenging.

“Flavour compounds such as vanillin (which gives vanilla notes) and tannins (a contributor to structure and mouthfeel) are present throughout the trunk of a French oak tree. However, the concentration of vanillin varies in different sections, while tannins are more concentrated at the base of the trunk,” says Alexandre Sakon, founder of ASC Barrels. This means casks produced only from staves made from specific parts (such as the upper section) of a single tree will produce different results than a cask made only from other parts (such as the lower section).

Likewise, there can be significant variation in the qualities of oak sourced from within a single forest, or a single part of a single forest. The solution to this propensity for variability is to create consistency via a process known as blending. “Staves are always a blend of oak from different trees,” explains Alexandre, “which we do to average
out the influence of the wood. Casks made of staves originating from the same tree only happen on request, and very rarely.”

The subsequent process of toasting and charring casks is vital as heat ‘activates’ flavour compounds within the oak. But the extent to which this ‘homogenises’ the potential of each cask depends on the grain. “Our cooperage receives oak from the Ozarks, Appalachian and Northern forests, and oak from these regions can have either open or denser grain. This is significant as the same charring and toasting regime penetrates deeper into open grain than it does into denser grain, which means open grain has a deeper layer of flavour compounds which the maturing spirit can extract,” says Chris Morris, master distiller whiskey innovation, Brown-Forman.
Woodford Reserve Distillery warehouse

Each cooperage has its own definition of light, medium and heavy toast, and degrees of charring. This means casks from the same cooperage offer a certain consistency, though in the past 10 years it has become increasingly common for distilleries to source casks from more than one cooperage, which inevitably increases variability. Additional influences come into play in ageing warehouses, but specifying dunnage or racked is only an elementary distinction. Every warehouse of either type hosts a series of microclimates, whether warmer and drier, or cooler and more humid, with greater or lesser air flow.

“The same cask types behave differently depending on the conditions in a warehouse: in warmer temperatures the casks are more expressive and a more active influence on the maturing spirit,” continues Alexandre. Consequently, certain locations within a warehouse can provide a natural habitat for single-cask contenders.

Jack Daniel’s Single Barrel releases always come from the top floor of a warehouse, where the casks are exposed to the highest temperatures and dryness, resulting in the most robust expressions of the Jack Daniel’s flavour profile,” adds Chris. This doesn’t mean that casks are laid down with their destiny already assured. It’s a case of monitoring development and spotting star quality.
Jack Daniel"s cooper setting the staves

“The day in, day out routine sampling of Balvenie does reveal natural variations but these are subtle differences which are also pretty consistent. Any outstanding casks get marked up as a potential single-cask release. Occasionally we also get a cask that is off the scale – hugely full of spice, for example,” says Brian.

Older whiskies may be expected to have an advantage, but whether they are bottled as a single cask is always down to quality. “A 15- to 18-year-old can often be a really nice age for a single cask, when a lot of good things come together: great character, flavour and a bright freshness,” says Iain Weir, brand director at Ian Macleod Distillers. Nevertheless, despite their popularity among whisky enthusiasts, single-cask bottlings are still quite uncommon in the overall scheme of things.

“Out of 100 barrels five might be considered good enough for a single-cask bottling. When you find one it’s an immediate reaction: wow. I’m looking for the ideal first-fill Bourbon and first-fill sherry – a utopia, which not every cask can give you. There are different ideas about what is ideal in the industry; for first-fill Bourbon I don’t like too much coconut. And you want the distillery character to show through,” says Stuart Harvey, master blender at Inver House Distillers.

Another illuminating statistic is the quantity of whisky a single cask yields. By its very nature, such a bottling is always going to be in short supply. “Filling at 63.5% ABV can result in a 15-year-old malt with a cask strength of 56% ABV, which means a Bourbon barrel yielding 200 bottles, and a sherry butt 600 bottles,” adds Stuart. Such exclusivity is an integral part of the allure and emotional appeal that single-cask releases exert. Emotions may be more difficult to quantify than a ‘tech spec’, but they are definitely experienced – and can be just as intense as the spirit itself.