The little cask that could

Rarely seen and small in stature, the oft-misunderstood octave cask nevertheless has lots to offer whisky makers
By Dr. Chris White
As with the advent of many of history’s great inventions, the octave cask was not the product of fastidiously and carefully developed methodology, but rather the consequence of serendipity – a happy accident. It stands among countless other items that we now take for granted: penicillin, Coca-Cola, microwave ovens, and even cornflakes were unexpected and fortuitous discoveries made whilst in pursuit of something else. Indeed, the same can be said of the effect oak casks used to transport Scotch across the country – sometimes legally, sometimes not – had on the colour, aroma, and flavour of the spirit contained within.

In the often-romanticised 18th and early 19th century, when the clandestine operations of illicit distillers and smugglers were gradually transformed into a strictly governed and regulated industry, whisky would have been smuggled out from remote, hidden pot stills by any means possible. In central and northern Europe, wooden casks had been used for many centuries beforehand to store anything from vinegar and pickled fish, to precious metals and gunpowder – and likely everything in between. As such, they were considered the vessel of choice for transporting Highlanders’ precious liquid from the mountainside to the marketplace.

The 1800s were also a time when the popularity of sherry was booming in the UK, with casks of sherry – as well as port, cognac, brandy and wine – arriving from the Continent on a daily basis.

Indeed, a ‘pype of seck’ (cask of sherry) is recorded as having landed at the Port of Leith, on the outskirts of Edinburgh, as far back as 1548.

Once on British shores, the sherry would have been consumed locally, or distributed across Scotland and the extended British Empire. Surviving newspaper clippings from the 1850s describe octaves of sherry for sale in the far-flung colonial outposts of Australia and New Zealand, showing just how widespread its popularity was across the globe.

Following the introduction of the 1823 Excise Act, duty was levied on the volume of proof gallons a distiller produced. This meant distillers sent their whisky straight from pot still to market. They used what was readily available, which was the plentiful and continual supply of sherry casks. In addition to using the huge but rather cumbersome butts in which the sherry arrived from Spain, much smaller and more easily manoeuvrable casks were coopered: octaves.

Octave casks – from the Latin octavus, meaning ‘eighth’ – are 45-50 litres in size and are so named because they are approximately one eighth of the volume of a sherry butt. Aside from their historical use in shipping sherry internationally and transporting whisky domestically, they have been used in the modern era by several whisky companies, most notably the family-owned Duncan Taylor in Aberdeenshire.

Duncan Taylor trademarked the name ‘The Octave’ more than 15 years ago, but its experimentation with these casks extends back to the 1970s, when chairman Euan Shand was an apprentice cooper. He recalls, “When I first left school I joined my father at The Glendronach Distillery Company, which he managed. I became a trainee cooper and one of the disciplines was to make small casks to learn our trade.”

Shand’s involvement with these casks didn’t end with their creation; he went a step further. Filling his casks with whisky, he noticed that the smaller casks created a remarkable, rapid change to the spirit. “I knew I was on to something that nobody else had even considered back then,” Euan reminisces.

This rapid change, or ‘accelerated maturation’, is primarily driven by an increase in the ratio of oak contact area to volume of spirit. Octave casks have a significantly higher ratio compared to butts, hogsheads, and even barrels, meaning that maturation, in terms of surface-dependent biochemical reactions, is ramped up in these mini cauldrons of oak and whisky. Because of this, octaves are rarely used for long-term maturation, with Shand explaining he fills them for three, six, and nine-month finishes. As such, arguably the most important aspect to consider is the plethora of volatile compounds which are swiftly extracted from the wood in the initial stages of maturation.

Oak is primarily comprised of cellulose, hemicellulose, and lignin, with the latter two categories contributing significantly to an octave’s somewhat aggressive influence on the spirit within. While cellulose is relatively inactive, hemicellulose contains several different sugars and is easily broken down during charring or toasting, resulting in a range of extractable aroma compounds, including furfural, maltol and cyclotene, which give rise to almond/walnut, sweet/malty, and caramel/liquorice notes, respectively.

Lignin’s components – guaiacyl and syringyl – are broken down into compounds which go on to form aldehydes, acids and phenols. These include highly aromatic compounds such as guaiacol (smoky notes), 4-vinylguaiacol (clove spiciness), phenyl ethanol (floral tones), and vanillin (vanilla, unsurprisingly). Perhaps the best-known, and possibly best-understood, oak extractives, are the two isomers (mirror images of one another) of oak lactones, cis- and trans-oak lactone. The cis form gives the classic coconut notes associated with American oak, whereas the trans form manifests itself organoleptically as notes of clove and woody incense. There are also the not-insignificant roles of sherry seasoning and tannins to consider, with the latter providing astringency, bitterness, and spice, as well as adding viscosity.

Given all of the above, the management of octaves is much more involved compared to larger casks. “There is definitely a little more hand-holding needed to keep on top of the progression of flavour and the higher rate of evaporation,” says Greg Urquhart, operations manager at Gleann Mór Spirits. That progression of flavour is most markedly seen in the first fill, which is why Urquhart prefers octaves on their second fill. “I find the first fill can be very aggressive if it isn’t monitored closely,” he explains.
Shand agrees, but after more than 40 years of working with octaves he says that for him their use is never a stab in the dark. His team have “a huge database of information on maturation, evaporation, and flavour profiles”.

The versatility of octaves is also readily seen in Duncan Taylor’s inventory, with Japanese, single grain, gin, rum and some other more obscure types of spirit currently ‘octivating’, as Shand refers to the process, in their warehouses. Sometimes, however, it’s not about creating something weird and wacky, but steering an already high-quality spirit down a particular path.

“We finished an 11-year-old Islay whisky in a second-fill Oloroso octave and it took what was an already excellent example of a beautifully peated malt and elevated it to something we completely fell in love with,” remembers Urquhart. In addition to enhancing a good whisky, it is an octave’s unique ability to rejuvenate which really allows it to shine.

While some might see octave casks as something of a blunt instrument, when used with the underlying science, they are proof that good things do indeed come in small packages.