First-Fill Casks Aren’t Necessarily The Best Thing For Your Whisky

One huge advantage of private cask ownership of Scotch whisky is the opportunity it gives to raise and nurture the spirit in the way you’d like. This blog focuses on one small decision in whisky cask management with potentially warehouse-shaking ramifications: To first-fill, or not to first-fill?


First Fill

That first taste of whisky from your own cask – magical.

Primacy. We’re hard-wired to love it. First place, first prize, first among equals – where’s the glamour and glory in coming anywhere other than first?

On the surface of it, this would appear to be an enduring truth in the whisky world as well. ‘First fill’ casks are highly prized, and often mentioned on the labels of great Scotch whiskies. 

A first-fill cask is exactly as it sounds… sort of. The name comes from the cask having been filled for the first time with Scotch whisky. But that’s not the first time the cask has been filled with anything at all – almost every cask we use in Scotland has already been home to something else. ‘First fill ex-bourbon’ casks come to us from the USA, having already matured whiskey there. ‘First fill ex-sherry’ casks come to us from the bodegas of Spain, having been seasoned specially for the benefit of maturing Scotch. To get even more ‘first fill’, and have your whisky go into a cask that has never known the sweet kiss of any other liquor, you’ll be wanting ‘virgin oak’ – still a rare sight in Scottish warehouses.

So – first-fill. A cask that’s younger and flush with the exciting flavours of oak and the previous liquor. Not a washed-up, has-been ‘refill’, already rinsed clean by long years of maturing Scotch. First fill is obviously more desirable, right? 

Like everything else in life, it gets more complicated on closer inspection. 

*Note: it actually gets FAR more complicated that I can should reasonably go into here. For ease, comfort and pleasure of reading, what follows is a greatly abridged bio-chemical history of life in the cask. For the masochists among you, click here.


The Additive Approach

The most obvious benefits that casks bring to the whisky are the colours and flavours that they add to the spirit. Whisky starts its life as innocent and pale-of-cheek as a glass of tap water. For a healthy, ruddy complexion, a first-fill cask adds beautiful, caramel-dark layers of colour to a whisky in short order. 

While it’s busy doing that, flavours from the cask wood are also infusing the whisky, adding new sensory notes on top of the liquid’s existing flavour profile. Tannins, vanillins, wood sugars and coconutty lactones all readily transfer from cask wood to whisky, increasing its complexity and fragrance.

Here’s the thing – you can’t tell a cask to stop. It doesn’t have an off-switch. Like a teabag, it’ll continue adding flavour to a brew, right on past the point of over-steeping if you don’t take matters into your own hands. ‘Over-oaking’ is a phenomenon in the whisky world, an issue faced by the longest matured casks.

Particularly potent casks (Virgin oak and ex-sherry especially) need to be treated with caution. Medium to long maturations in first-fill can bring about some incredibly intense changes, which may or may not be desirable. It all depends on what you want from your whisky.

Charring the inside of a cask helps to remove off-notes. This is especially common in American oak casks.

Perfection is when There is Nothing Left to Take Away

If maturing whisky was all about adding new flavours, we’d probably have moved to the gin model of infusing our spirit with botanicals by now. There’s a reason why the most highly regarded whiskies are kept in oak for many decades – and it’s not just about what gets added. We also consider what gets taken away.

Oak wood giveth, and oak wood taketh away. Oftentimes it also transformeth, but we’ll getteth to that hence.

Aside from the renowned ‘angels’ share’, in which alcohol evaporates out through the pores of the cask, whisky also loses more elements of itself along the way. Don’t weep for these lost aspects of the spirit – they’re often quite feisty and challenging to the palate. 

Sulphur, for example – it can manifest as meaty or brassica-farty aromas in the whisky. The former can be rather pleasing (Mortlaaaaach!), while the latter is resolutely not. Fortunately, the charcoal layer of charred casks is effective at removing sulphurous off-notes from a whisky, but this does require time to work effectively.

Different char and toasting levels can tailor the impact of the cask on the whisky (photo taken at Holyrood Distillery, Edinburgh)

Many more volatile flavour compounds can be quite shocking and peppery on the nose in a

younger whisky, and a slow process of maturation gives time for such volatiles to either escape the cask, be absorbed by the wood, or be transformed into something more benign. Acrolein is one such example. Frequently found in youthful spirits, it brings a horseradish kick to the palate, which perhaps recommends the whisky as an accompaniment to roast beef, but little else. As casks breathe, acrolein oxidises to acrylic acid. A little milder than acrolein, it is often described as having a ‘tart’ aroma, which implies a certain citrussyness, which works a little better with whisky than horseradish does…

There’s also the added angle about being careful with resources. If casks are able to perform well for many decades, it makes sense to make use of plentifully available resources rather than pursuing the new. But that’s an aside to this discussion.


Suitable for All Ages

Here’s the kicker – subtractive and transformative processes happen in casks of any age. First-fill, refill, ancient and creaking; the use of the cask may influence the added flavours in the whisky, but truly mature Scotches rely on the slow release of volatiles over time; the oxidation and reduction of astringent properties into velvety and gentle elements. This is a process which can’t really be rushed – it simply requires a decent oak cask and many seasons of rest. Refill casks do not transfer huge amounts of colour, so this process means that even pale whiskies can have surprising depths of flavour.

A previously-used cask will still transform the interred whisky in subtle and important ways – those which are most important for well-aged whisky to be regarded as mature and desirable. 

A tidbit from Jerez – the best solera casks used to mature sherry are old heirlooms, kept for decades; no longer able to impart much flavour to the wine. It’s the reductive effects of cask maturation that are desired for classic sherry maturation. Sherry makers want the original flavours of the wine to remain at the forefront, tempered by time perhaps, but not much added to by an active cask. 

Whisky makers and private cask owners are able to choose according to their priorities – what kind of whisky do you want to produce?

Distillers are experimenting more and more with different styles of barley to make their spirit. A dominating cask could hide the subtler differences between these different methods (This particular barley regime is from Holyrood Distillery, Edinburgh)

What Kind of Whisky Do You Want to Produce?

That is the question that has been asked by master blenders and expert distillers, and now it also falls to the independent bottlers and private cask owners. The work of distillation is all done, but the choice of cask will determine the type of whisky that is eventually produced.

During Stage 1 of the Cask Ownership Process, when you are talking to our team and selecting your cask, the great majority of casks on offer will be ex-Bourbon hogsheads. You’ll want to pay attention to whether they are first-fill, or refill, though. A first-fill will give much more of itself to the whisky, especially those flavours of vanilla, coconut and smooth oak that Bourbon is known for. A refill will give less to the whisky, but still allow for sharp, tannic or spicy notes to dissipate; leaving a whisky that is a more refined version of the originally distilled spirit. The fruitier esters and aldehydes that are generated in the cask may be given more of a chance to come to the fore in this case. And if the distillery had an unusual approach during distilling? That will be better preserved in a refill cask.

As with so many things, an all-or-nothing approach is not necessary – cask owners can have cakes and eat them too. If you’re a cask owner in Stage 3 (Cask Maturation), you will know that a re-rack is always an option. Mixing and matching casks is often a great idea, and a common practice sees refill casks used for the majority of a whisky’s maturation, followed by a re-rack and a period spent in a first-fill or otherwise seasoned cask. That way you get the benefit of careful and slow coaxing of mature flavour through the transformative and reductive processes, followed up by a growth spurt of flavour and aroma in a cask that has extra flavours to freely give. The icing on the cake, as it were.

The choice, as ever, is yours. But we implore you – don’t overlook the humble refill cask. Sometimes a softly spoken voice can be the most influential.

There’s a world of Casks out there. No two are exactly alike.

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