Why is whisky stored in casks?

The final flavour of whisky depends on many factors. In Scotland, by law, the whisky aka spirit must be stored in a cask to mature for a minimum of three years before it is even called Scotch whisky! During these three years, the spirit absorbs, is influenced by the cask it is stored in, and hence, it is important to note how different types of whisky casks contribute to whisky flavours. 

Factors like the type of wood being used, the previous liquid stored, age of the cask and the size matter a lot. Experts state that approximately 60% to 80% of the whisky flavour comes from the cask. 

Let us look at the various types of casks used to store whisky and the flavours they bring out in the spirit: 

Whisky casks are made using American White Oak (Quercus alba) or European Oak (Quercus robur). With an American oak, the flavours derived are sweeter, softer with caramel and vanilla notes. On the other hand, with the European oak, the whisky flavours are spicy, dried fruits and tannic. European oak used for whisky casks is grown in Portugal and Spain region. French oak is often used to store and age wine and cognac. 

Cask Influence

Size matters, and how! Size of the cask dictates the ratio of the wood coming into contact with the spirit, e.g. a smaller cask (quarter cask -125L or American Standard Barrel – 200L) will have a higher ratio of wood contact to spirit versus a bigger cask (Port Pipe- 550L or Madeira Drum – 650L). Hence the bigger the whisky cask, the longer it takes the spirit to mature. 

1. The hogshead cask is made by dismantling ex-bourbon barrels to create a bigger, larger cask. It is a preferred choice in the Scottish whisky industry as the bigger size allows for better ageing of spirits.  

2. A wood finish cask is commonly known as a barrel. It is made using Irish, American or Japanese oak and can store upto 200-500 litres of spirits. Its typical flavour influences on the whisky are sweet oak, spice and vanilla.  

3. A wine finish cask is commonly called a barrique or a barrel. It is made using French oak wood and can store upto 220 litres of spirits. It adds various flavours to the whisky and wine stored in it.  

4. A port finish cask is known as a pipe or barrique and is made using French oak wood. It is larger and can store upto 600 litres of port pipe or 220 litres of port barrique. It adds flavours like red currants, sultana and berry fruits.

5. A sherry finish cask is commonly called butt or a puncheon. It is made using American or European oak wood and can store upto 500 litres of spirits. It adds flavours like dates, sultana and walnut. 

6. A Madeira finish cask is commonly called the drum and is made using the Portuguese oak wood. It can store up to 650 litres. It adds flavours like fig, spice and of that of sweeter fruits. 

7. A rum finish cask is also known as a puncheon and is made using the American oak. It can store upto 500 litres of spirits. Its flavours include vanilla, tropical fruits and Molasses. 

8. A beer finish cask is known as the barrel and is made using American oak wood. It is smaller in size and can store upto 200 litres. It adds a sweeter, creamier and malt flavour to the spirit stored

Charring and Toasting

This is an essential part of the spirit-cask relationship. Through the toasting and charring technique, the wood sugars are converted into caramel and vanilla flavours. And what distinguishes the charring from toasting? While toasting darkens the wood top and acts in the depth of the staves, the wood is left with a flat blacktop layer. While charring, the wood is burnt to a point where its surface breaks and the wood is left with an uneven structure. Experts call this as crocodile skin. 

The time taken for the barrel to burn determines the level of charring. It also depends on the specifications required by the distillery ordering the charring process for the cask. 

Reuse of the cask

It is essential to note the number of times a cask has been used. The more a cask is used, lesser the influence it imparts on to the whisky’s flavour. For Bourbons, it is mandatory to use new charred oak barrels “better aging and colour characteristic”. For other spirits, casks are rejuvenated before they are refilled. To rejuvenate the cask, it is milled from the inside and then charred. This helps restore the caramel and vanilla flavours for the spirit.

But this is not it as there is more! Let’s talk about different types of experimental whiskies.

Glenfiddich IPA Cask

As one of the first entries in the Glenfiddich Experimental series, this is whisky finished in casks that were seasoned with India Pale Ale. The Speyside craft brewery first created an exclusive beer which was then aged in old Glenfiddich casks for a month and then the casks were returned to the distillery. Whisky was stored in these casks for three months, and the final result was a fruity and vibrant flavoured dram!

Glenfiddich Grand Cru

This whisky is matured in a number of small-sized ex-sherry casks and American oak casks. It is finished for four months in in a combination of first-fill and second-fill French oak casks, previously used for fermenting wine that was to be Champagne. This whisky offers vanilla, brioche, pear sorbet and white grapes notes along with aromas like apple blossom, lemons and freshly baked bread.

Jameson’s Caskmates

This whisky is stored in reused old whisky barrels. While this is not new, but before storing whisky, its cask is used to age stout from Cork’s Franciscan Well brewery. Doing so, added notes like butterscotch, coffee, cocoa, etc. to this Irish Whisky. 

Dalmore King Alexander

This whisky is indeed a masterpiece! To make it, master distiller Richard Paterson selected differently aged malts that matured in a mixture of French wine casks, sherry butts, Madeira drums, marsala barrels, bourbon barrels and port pipes. Marriage of six different casks is extremely rare in the industry and by doing so, the whisky offers notes such as chocolate, nuts, spiced raisin, vanilla and toffee.

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