Much has, and more than likely will be, written about cask strength whisky – the disgorging and bottling of liquid at its then settled and natural ABV without any further dilution. But, fewer articles focus on the fact that most whisky has indeed been reduced in alcoholic content prior to be being filled into cask. Spirit ABVs vary – from grain to malt and across different equipment setups – what you get out in new make form varies - even between runs if you’re taking a more hands on approach. And yet, there are commonalities with filling strengths, and in malt terms (and particularly across Scotland), 63.5% has been employed as an industry standard for over 70 years. But whilst this diluted ABV is widespread, not every distillery utilises it – indeed, some (particularly in the craft sector) are experimenting with lower filling strengths and their effect on maturation.
63.5% is not utilised the world over – indeed, when you look across the different distilling countries, you’ll find reasonable wide variance on filling strength. In the US thing are somewhat more restrictive - bourbon and corn whiskies are legally required to be filled at a maximum proof of 125 (62.5%). But over in the UK, it currently seems to be more of a guideline and less of a rule.
The Scotland Technical File notes that spirit is “…..normally diluted with water to a strength somewhere between 60% and 70% ABV”. In Ireland filling strengths are similarly noted in their Technical File as being between 63-70% (I’m aware of some fills higher at 71%). But, in both cases, there is more specificity on the upper confines of the alcoholic content of the distilled spirit and the minimum 40% ABV when bottled. That middle section – the maturation piece. That’s up to individual producers to work out.
Whilst filling at 63.5% has become established as something of a norm at many distilleries (more on that shortly), you might note some older Scotch single malt whiskies with particularly high bottling strengths. There are always anomalies. One such is during the period of the whisky loch, where producers (particularly DCL) were noted as filling still strength spirits to both reduce their warehousing costs, and likewise to cut down on the overall number of casks required. See DCL’s Rare Malt series for a prime example of these higher strengths where despite the reasonable lengths of maturation, bottling ABV remain exceedingly high. In these circumstances, one would expect that the higher ABV filling has resulted in slower alcohol evaporation and a faster maturation (a higher level of extraction vs the time spent in cask). But similarly, some interesting aroma and flavour profiles due to certain alcohol solubles (aldehydes, terpenols etc) being more extractable at higher strengths.
So where did 63.5% ABV come from and why has it generally stuck around? Historically, this ABV was known as ’11 over proof’ and it was one of two legally acceptable alcoholic strengths (the other being 23 over proof – 70.2%) which distillers were allowed to sell to rectifiers – companies who redistilled the spirit to purify it enough for consumption. Back in history, mixing it with vegetable by products to obtain flavour – the utilisation of oak casks came later in history.
However, the science of filling strength was not looked in to until much latter – the second half of the 20th Century. A variety of studies compared the interaction of the spirit with the wood across a wide variety of proportions of water to ethanol and concluded that 63.5% ABV (irrespective of its historical pegging) was in fact the ideal strength for an optimum spirit interaction – comparing the level of overall total extraction with that of variety of other transformative compounds – including phenols. The practice steadily became commonplace and the filling strength was simply normalised.
What this initial research did not look into however was how the level of extract varies according to the age of the whisky. And now, some producers are starting to experiment with filling strengths to note whether both the size of the cask, and indeed its expected maturation length have a bearing on whether the established norms of 63.5% still hold true. A range of distilleries are therefore exploring dilution pre filling, noting that both the variance of interaction and extraction levels, as well as the ability to accurately gauge their desired bottling strengths and ergo omit the need for post maturation potable water. In essence a new formulation of cask strength – filled lower, but then with no need to modify the ABV prior to it being offered to the customer. I await the results of some of these experiments eagerly.
Irrespective of its filling strength, today’s review bottle has seen some real activity over its 21 years of maturation – a Glentauchers on the cusp of Scotch whisky legality at a lowly 40.8% ABV and with a hue that would turn the head of any self-respecting sherried whisky fan. The liquid is noted as having been drawn from a Pedro Ximenez octave and though not listed as being a finish, I can only imagine this being the case.
Indie bottler Duncan Taylor started experimenting with these 50L ‘mini casks’ some 15 years ago – prior to that, their usage was as a coopering training aid, in effect a chopped down butt – but at that point, not filled with whisky. Over the years, the company has introduced a range of octave finished whiskies – and indeed, let their marketing team run amok with a whole new lexicon: octivation and octave invigorated ™. The essence of the finishing being a rapid, concentrated second maturation in a smaller cask with a higher wood to liquid ratio. But 21 years entombed within one of these tiny casks? I’d be truly astounded.
Chorlton Whisky, who we’ve criminally not written about to date (a relatively newer, smaller and regularly excellent bottler with a highly recognisable label design) have used a PX octave to produce a mere 73 bottles of 21 year old Glentauchers – released back in 2018 and costing (if memory serves) around £65-70. I snapped one up quickly – Chorlton bottle nice things. Any that were left by that summer then immediately disappeared after the release was named as the best in show at the very last, and sadly missed Dramboree. Word obviously got out that this baby was a wee bit tasty – the last auction price I can find was at SWA’s final auction of 2019 – a cool £170 plus fees.
Nose: Big fat PX sherry – sticky and full of expressive aromas. Plenty of cocoa powder alongside chocolate sauce and royal icing. Candied orange peels, strawberry jam and plump raisins sit with bread and butter pudding whilst notes of wood polish and rancio are joined by manuka honey, cinnamon and pencil shavings. Virtually no room for reduction (if you’re wanting to hold it above 40%), but a drop or two is still transformative – gingerbread men, walnuts and cashews alongside creamy strawberry yoghurt.
Taste: Thick, coating and clingy. Caramel sauce, butterscotch, Dulce de leche and cocoa nibs sit with sultanas, raisins and fig rolls. All rather sumptuous. Brandy snaps and sponge cake mix are joined by waffle batter and lightly toasted oakiness. The result bringing a feeling of Armagnac to the affair. Reduction (again, super sparingly) reveals some of the age of the liquid with light tropical notes of dried mango slices. It also dials down the ‘fatness’, expressing creamy qualities of fudge and burnt toffee cream.
Finish: Medium with sticky toffee pudding, fading berry preserves and discernible, but pliable tannins – rather well hidden by the continued viscosity of the liquid.
The first thing to note about this Chorlton Glentauchers is its wonderful mouthfeel – dense and heavy - despite its low bottling strength (was that Octave completely emptied prior to filling?!). The slightest touch of reduction then offers a highly velvety and buttery texture - whilst there’s little room to manoeuvre on ABV, there’s seemingly more scope for modifying the weight of the liquid. I’ll take that. Being critical, the Tauchers character feels rather subsumed by the impact of the sherry, and complexity levels have been lessened as a result. But purely from an enjoyment point of view I find this to be both exceptionally tasty and decadently rich – therefore it still scores well.
But don't take our word for it..
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