Understanding Cask Sizes and Types

So you are thinking of purchasing your own cask of whisky, or maybe you already have and now are wondering just how many bottles you are likely to produce from a single cask.

This can sometimes be a bit of a guessing game, so be prepared because a cask can hold anywhere from 50 to over 750 x 700ml bottles at cask strength when first filled. Of course a cask is handmade, albeit by incredibly skilled craftsmen, but there is still a level of variation and no two casks are the same.

The best place to start is to understand just what a ‘cask’ is. The term cask is the general category for a container used to store liquid, typically alcohol. Not to be confused with a barrel, which is actually a specific type of cask.

Below we list some commonly seen cask sizes that may be used commercially in the whisky industry. We have also shared what those litres mean in bottles at cask strength. Bare in mind that angels share losses will vary what the final outturn will be.

• Bloodtub 30-40L: Very rarely used commercially as it has such a small capacity, which encourages rapid maturation. Approx. 50 bottles at fill.

• Octave 50-65L: An eighth of a butt, sometimes used for small batch production and speedy cask finishing and experimenting. Approx. 82 bottles at fill.

• Quarter Cask 125L: A quarter of a butt which is the perfect vessel for influencing a whisky for finishing over a 12 months period. Approx. 178 bottles at fill.

• Barrel 200L: An American Standard cask size and commonly used for bourbon maturation over 3-10 years. Approx. 285 bottles at fill.

• Barrique 225L: Used commonly to mature red wine, sherry and other European drinks often made from European Oak. Approx. 321 bottles at fill.

• Hogshead 250L: One of the most commonly seen cask sizes, typically used for Bourbon and long term maturation of 10+ years. Approx. 357 bottles at fill.

• Port Pipe 350-400L: As the name describes this cask size is used in the Port industry in Portugal. Not as commonly seen as sherry but prized among whisky producers. Approx. 571 bottles at fill.

• Butt 500L: The butt is a prized possession and often used to mature some of the finest sherries in the world, thick staves and tall stature allow for slow and steady maturation. Approx. 714 bottles at fill.

• Puncheon 500-700L: A vessel that is typically seen when maturing rum or sherry with very thick staves allowing for a slow maturation and high ages when used for whisky maturation. Approx. 857 bottles at fill.

• Gorda 700L: Not often used for maturation as it is very close to the maximum size permissible to mature Scotch Whisky. However it is an ideal vessel for marrying multiple casks (vatting) prior to bottling very slow maturation. Approx. 1000 bottles.

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The Role of Maturation and the Angel’s Share

Now that we know how many cask types there are and how much variation there can be in fill levels, we are getting a good idea of the basics. But here is where it gets really interesting, where the magic happens.

While a cask is filled to the brim at a predetermined alcohol strength, this is where the intention stops, and we start to be at the whim of the angels. Maturation is of course, the magic of the whisky interacting with the wood it resides in over the many years of warm summers, wet autumns, cold winters, and fresh springs.

With this climate fluctuation, coupled with the fact that casks are not airtight, there is the phenomenon of evaporation, affectionately referred to as the ‘angel's share’. Both a blessing and a curse. This is how whisky matures, which is after all a necessity, though for this, we must pay the angels their tax.

You can expect approximately 2% of the volume to be lost per year to the angel's share and approximately 0.5% per year of ABV loss. I stress these are approximations, as a warmer-than-usual summer will see a greater drop, and the earlier years of a cask's life will tend to see a high % drop, which tends to slow as the years go by.

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Calculating Cask Contents and Re-gauging

Now, with the above average loss calculations, you can get an approximate idea of how many bottles you might still find in any given cask, but it is not an exact science. To be more precise with a cask's contents, we can carry out a ‘re-gauge’. This is essentially a health check for the cask and the whisky inside, telling us exactly how many litres of alcohol are remaining, how many bulk litres of liquid, and the current % alcohol content. A dip re-gauge is a rudimentary option where we get close approximations. A full re-gauge requires the cask's contents to be emptied and measured, which provides exact figures and a full picture of the cask and its contents.

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The Bottling Process and Final Yield

Now that we understand casks and maturation, there is one more consideration: bottling.

When bottling a cask, there is a little more to consider when looking to understand the final outturn of bottles. There are some production losses to be expected when bottling due to filtering, pipe pressure and auto-filling machinery. Commonly around 2-8 bottles may be lost in this process. Auto-filling machinery also has a minor tolerance of 2% either way, meaning that your 700ml may end up being 10ml higher or lower, which over 250 bottles can quickly add up.

And finally, you have some choices to make, which will vary the number of bottles produced quite considerably. Glass bottle size is an obvious factor; a 500ml bottle will produce more units than a typical 700ml bottle would. A less obvious factor is bottling alcohol strength; you’ll have seen the term cask strength, which refers to whisky that has been bottled directly at the ABV found in the cask. However, common bottling ABVs can be seen at 40% or 43%. Reducing ABV is managed by adding distilled water and, therefore, increasing the volume of liquid available and increasing your bottle count. Though a purist would always place a higher value on a full unadulterated cask strength whisky.

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The Joy of Whisky Cask Ownership

So there we have it, a fairly comprehensive guide to the number of bottles you might find in a cask. Though this, of course, doesn't account for your enjoyment of samples over the years of maturation, which is one of the best things about owning your own whisky cask: drawing some sample drams for ‘analytical purposes’ and making sure it is maturing in the way you want.

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Start Your Whisky Journey

Owning a cask of Single Malt Scotch Whisky is about understanding its unique journey and enjoying the rewards. To explore purchasing your own whisky cask, speak to our expert team at info@tailoredspirits.co.uk and we will be happy to guide you.