Have you ever wondered just how much whisky is hiding away within a whisky barrel? 

This can be a bit of a guessing game, so be prepared because a cask can hold anywhere from 50 to over 750 x 700ml bottles of whisky 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.

• Bloodtub: 30-40 litres or a dinky 57 bottles
• Octave: 50 litres or unique 71 bottles 
• Quarter Cask: 125 litres or a respectable 178 bottles
• Barrel: American Standard 200 litres or a solid 285 bottles
• Barrique: 225 litres or a specific 321 bottles
• Hogshead: 250 litres or an impressive 357 bottles
• Port Pipe: 350-400 litres or a heavy 571 bottles
• Butt: 500 litres or a handsome 714 bottles
• Puncheon: 500-700 litres or a monstrous 1000 bottles

Now we know just 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.

Whilst 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 ‘angels share’. Both a blessing and a curse. This is how whisky matures 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 angels 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 casks life will tend to see a high % drop which tends to slow as the years go by.

Now with these calculations you can get an 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 casks 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 regauge is a rudimentary option where we get close approximations, a full regauge requires the casks contents to be emptied and measured, this provides exact figures and a full picture of the cask and its contents.

Now 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 losses to be expected when bottling, due to filtering, pipe pressure and auto-filling machinery. Commonly around 5-15 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 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 ABV’s can be seen at 40% or 43% quite commonly. Reducing ABV is managed by adding distilled water and therefore increasing the volume of liquid available.

So there we have it, a 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.

To explore purchasing your own whisky cask, get in touch with us here.