Why Does the Cask Matter So Much?

There are many factors that contribute to the final flavor of whisky. In Scotland the spirit must mature in casks for a minimum of three years before it is legally allowed to be called whisky. In this time, the spirit will be heavily influenced by the cask it’s been in, therefore it is important to understand how these casks contribute to the product. The type of wood used, age, size and the previous liquid in the cask all matter. It is said that 60–80% of the taste comes from the cask!


Most whisky casks are made from either American white oak or European oak. American oak gives a softer, sweeter taste with notes of vanilla and caramel, while European oak is spicier and has a stronger wood input. European oak grows in northern Spain and Portugal. French oak is used to age wine and cognac. It will bring notes of vanilla, pepper and subtle spiciness.


Cask Size

The bigger the cask, the longer it takes the liquid inside to mature.


Toasting and Charring

All casks are toasted, but not necessarily charred. A new oak cask goes through a heat treatment, toasting, before any liquid is put inside. Toasting will caramelize the wood sugars. This process brings those lovely vanilla and caramel notes from American oak and releases more tannins and spices from European oak. These flavors will eventually get mixed into the liquid.


Number of Fills

Bourbon must be aged in new oak, so when whisky is aged in a 1st fill ex-bourbon barrel, this means it is the first time that malt whisky has gone into that barrel after bourbon. In this case, the whisky will be heavily influenced by the wood, and therefore the spirit is only left in the barrel for a short period to avoid heavy wood influence. This can be around five years.

In Scotland, the same cask can be used for many years, although it is uncommon for the cask to be refilled more than three times. So obviously, after the 1st fill you will have a 2nd fill, which averages around eight to twelve years, and, confusingly, the third and final fill is known as the refill. After the 3rd fill, the inside of the cask can be shaved to show new wood before re-toasting and charring.


To see the effect of a 1st fill ex-bourbon aged whisky check out The Glenlivet Founder’s Reserve.


Previous liquid


Bourbon barrels are made from American white oak. They go through both toasting and charring before the bourbon is added. Also, the ABV level of the bourbon will impact the flavors of the barrel – the higher the ABV, the bigger the impact on the wood. Basically, the higher alcohol level will strip the barrel of the benefits of toasting and charring, leaving less flavor for the next spirit.

After Scotch whisky has spent some time in an ex-bourbon cask, the Master Blender will mix together whisky from various barrels. These can be from the 1st, 2nd or the 3rd fill. Whisky aged in ex-bourbon barrels has a golden color and normally sweet and floral notes like honey and vanilla.


To try a Scotch blend using ex-bourbon casks try Chivas 12.


Sherry Cask

Sherry is a fortified wine from Spain, famous for it’s sweet and rich flavor profile. Sherry casks are made from European Oak and impart rich and intense character to the Scotch matured. Compared to the more mellow American Oak, the Spanish cousin is livelier and more characterful. Sherry aged Scotch can be seen to give a more creamy mouthfeel with extra layers of sweet, spicy and rich flavor notes.


To explore the effect of sherry cask you can try Chivas Extra.



By playing around with different cask types and sizes, the Master Blender can create layers of flavors. They can use a range of the same casks, for example, different fills of ex-bourbon, or mix and match a variety of cask types from bourbon to sherry cask.


Sometimes you must trust the skill of the Master Blender to use all the different casks like instruments in an orchestra, each cask, each single malt must be masterfully used to make a harmonious tune. To bear witness to the art of blending in action try Chivas 18, voted world’s best blended scotch whisky, with 85 flavor notes in every drop!


Our newest bundles at Gulp includes a bottle of Chivas 18, get yours now!