There’s much more to assessing the quality of a cask than simply leaning in for a bung hole sniff. Each cask possesses a unique history, some decades long, that will define the characteristics of any subsequent spirit maturation. Whilst we don’t believe that whisky creation is all about the wood (every ingredient and process helps forge the eventual profile of a whisky) – we do believe that careful selection and evaluation is vital for ensuring the best quality liquid.
There’s a host of information which can and should be gleaned from a cask prior purchasing it, or filling it:
How big is the cask?
The volume of surface-to-liquid area of a cask limits how much extraction is possible over a period of time – the greater the level of contact, the quicker this extraction of flavour will take place. Whilst a rapid extraction in a smaller cask might be desirable in some cases, the greater wood influence will need to be monitored and carefully controlled. In other instances – such as when casks have been earmarked for a longer maturation period, a gentler interaction is more desirable (few people like tasting overly woody whisky) and therefore a larger cask which possesses a lower liquid-to-surface area will likely be more suitable. Choosing the right cask size is a balancing act.
How many times has the cask been used?
Unlike the production of bourbon in the US, most single malt whisky casks are filled more than once. The greater the number of fills, the less activity there is remaining in the wood. During maturation, the spirit leaches out the sugars and compounds responsible for flavour creation from the wood steadily over time. With each subsequent fill there is less residue active compounds remaining in the wood and therefore less overall flavour to extract. Though of course, there’s still plenty of fantastic flavour possible to extract from a cask which has been re-filled – it just might take a longer maturation time to find that perfect balance between the spirit and wood.
What was in the cask before? and how long was it in there for?
Other than virgin casks, all casks come ‘seasoned’ with a previous liquid – and this previous liquid fill provides whisky makers with a palette of potential flavour profiles which can be imbued into their spirit during maturation. The most common fills are with bourbon and sherry, but there’s a wide range of potential liquids out there – port, various types of wine and fortified wine and even beer. Each will offer substantial differences in terms of how it interacts with the wood and the new make spirit – each creating a unique flavour of whisky. But it’s important to understand the traits of this liquid and also how long it was seasoning the cask for prior to it being refilled. Not all precursor liquids will marry perfectly with all spirits – even the most versatile ones. Similarly, a cask which has held sherry for three months will behave very differently to one which has held sherry for three years. Considering the qualities of the previous liquids, and their eventual destinations (are they a fine drinking sherry, or are they destined to become vinegar?) greatly helps to build an appreciation of how they’ll interact with a new spirit fill.
Bimber sources casks from a wide variety of locations. We’re largely agnostic about cask ‘brand names’ – what we’re more concerned with is the history and quality of the vessel itself. The more information we have about the journey of a particular cask, the more knowledge (and faith!) we’ll have that it’ll be ideal to mature our single malt in. And we’re picky about this. If casks are not up to our high standards, we simply send them away. In our mind there’s little point in spending many hours making whisky in the traditional way to waste its potential by filling into duff wood.
We’re very fortunate when it comes to wood. We’re proud to possess an onsite cooperage of skilled artisans who assist us in checking all our casks - repairing, re-sizing and re-charring our wood when its required. It’s a long established, but rare skill which enables us to take our carefully-crafted spirit and ensure that its long slumber is in safe hands. They’re our wood whisperers.
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