First fill vs refill casks

There are many factors in whisky that affect the flavour, but no factor is given as much credence as the cask in which the whisky is matured. Previous cask fill, oak type, cask size and even heat treatment are all given top billing when a brand talks about the casks they use. But the one that is perhaps the keystone of a balanced whisky is how many times the cask has been filled. Refill casks often get a bad rap, especially in an isolated context, but as a Master Blender, my job would have been impossible without the humble refill. So let's look at first fill casks and refill casks as well as what each brings to the party. 

For a deeper dive into the world of casks and maturation, check out these other guides:

The Whisky Club's guide to casks

The Whisky Club's guide to maturation

Is a first fill cask better than a refill?

The simple answer is that both are vital to many of the whiskies we know and love. It is true to say that a first fill cask will have more colour, more flavour and more oak character than a refill cask. But a refill cask will carry more of the distillery character, so it depends on what style of whisky you are trying to create. The rest of this guide looks at some of the nuance in casks and how first fill and refill casks can be used in combination to create new flavour profiles.

Cask fills

As the Scotch industry is the biggest whisky making industry in the world, we tend to use their conventions when naming cask fills. This might seem a little unfair to our American cousins, but when we talk about first fill, we are talking about the first fill of Scotch. The Bourbon or Sherry that was in there before is simply seasoning liquid and this seasoning liquid's job is removing undesirable and harsh oaky notes from the cask before the Scotch whisky enters the fray. Here's the hierarchy of cask fills and the language the Scotch industry uses...

What about colour and flavour?

I like to think of a cask like a teabag. The first cup of tea you make with a teabag is darkest, subsequent cups absorb less colour and different flavours from the tea leaves. Casks work the same way with each subsequent fill delivering less colour and less sweetness than the one before. 

After 2 or 3 fills of Scotch, many casks are effectively exhausted. The colour is very light and the flavour is much less sweet. A third fill European oak Sherry cask will resemble a second fill Bourbon cask in colour.

This is an actual image of a first fill European oak Sherry cask at 20 years old and a refill European oak Sherry cask at exactly the same age. Note the darker red colour in the first fill, this is due to tannins. When the cask is refilled, there is less tannin and colour compounds in the oak as they are all in the first fill example. 

Interestingly, Scotch distillers rarely use virgin or new oak casks as they can bring too much oak intensity and colour completely masking the distillery character. The tradition in Scotland has always been to buy used casks. These were mainly wine casks before the 1960s and have been predominantly Bourbon barrels afterwards.

How are first fill and refill casks used in the real world?

Let's look at a few scenarios:

1. You want to find two single casks to show off Bourbon casks vs Sherry casks.
   Here you definitely want a first fill cask. But it is unlikely you'll settle on the darkest and most intense tasting. Even in these releases you want to ensure the spirit style shines through. The darker and more intense flavoured and coloured ones are great tools for using in blends, but can often be oaky and astringent in isolation.
2. You want a perfectly balanced Aberlour Double Cask release.
   Notes of American oak, Sherry cask and distillery character need to be distinguishable. Here you will need three cask types: first fill Bourbon which will bring vanilla and caramel notes; first fill Sherry to bring dried fruits; and refill casks which will bring the blackcurrant fruits found in the distillery character. These refill casks are the hidden heroes of the blend.
3. You want a Sherry cask matured Glenmorangie. 
   You are working with one of the lightest new make styles in the industry and one of the most intense cask types. If you use first fill only, the distillery character will be completely masked. This is where refill casks are essential. They help ramp up the distillery character to compete with the intense Sherry flavours.
   
4. You want a peat monster.
   Here you can use casks to dial up or dial back the smoke influence. The sweetness of a first fill will make the peat seem less overt, whereas a refill cask will bring the peat smoke to the fore. 
5. You want The Macallan in Bourbon.
   The Macallan's spirit is notoriously full-bodied and perfect for maturation in rich Sherry casks. For it to work in Bourbon casks, you definitely need first fill all the way. This is a rare occasion where the spirit is heavy enough to overpower the cask, and therefore you may need a longer maturation period in Bourbon casks to achieve a sense of balance.

Does The Whisky Club use refill casks?

Yes. We recently released a single refill cask from an Orkney distillery. This whisky was selected to showcase the distillery's spirit character. Therefore the refill cask was perfect. 

For our whiskies of the months, refill casks will be expertly employed by the Master Whiskymakers. In our recent Bruichladdich 14 year old Islay barley, Adam Hannett used refill wine casks to bring hint of tannin and oak spice without overpowering the blend. Had he used first fill wine casks, all of the malted barley nuance would have been lost. 

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