Whisky in Bourbon Barrels

This article is not about how the Bourbon Whiskey is matured in the barrels, but how these casks effect the other Whisky or Whiskey (Scotch, Irish, Canadian, etc.) that are matured in the casks afterwards. Even though most of the Irish use the Whiskey spelling we will use Whisky for the successor Whisky and Bourbon for the first Whiskey inside the cask.

A finished American Standard Barrel (ABS)
A Finished American Standard Barrel (ABS)

1. Origin

The Bourbon comes from the United States of America. While the Bourbon Whiskey used to come from the Bourbon county located in the Commonwealth of Kentucky. Bourbon can now be made anywhere in the United States. If you like to know more about this circumstances please read our page about Bourbon.

2. Production

The key factors in the Bourbon production are the fresh American white oak casks, the toasting and charring of the barrels, and the mash bill. Please click on the links to learn more. 

3. Effect on Taste

Mash Bills

The mash bills are basically the list of ingredients that go into the fermentation process. The high corn content in the Bourbon gives the successor a sweeter character. This would otherwise not be possible with a high or 100% barley content, that most Scotch distilleries use. There are various Bourbon brands with different mash bills that result in diverse flavours. The variations arise mostly from the amount of rye in the mixture. The rye inside the Bourbon gives it the spiciness and the full body that you know from some Bourbons.

The mashbill of the Jim Beam Bourbon
The Mashbill of the Jim Beam Bourbon

The Barrel

First of all, the raw wood effects the taste of the whisky. The American white oak is a very mellow wood that contains only few tannins. This results in a smoother and milder taste of the whisky. Read more about the effect of the oak here.

The Second factor is the toasting of the barrel. The toasting of the barrel is a heat treatment process that transforms substances inside the wooden staves of the barrel. The wood sugars inside the oak are heated up to 150°C (300°F) and therefore caramelized. This is one of the major influences in the additive maturation of the Bourbon and later of the successive whisky. Here the Bourbon gets its distinctive flavours of caramel and vanilla. Not all of these wood sugars are dissolved into the Bourbon and some of them find their way into the whisky stored in the cask afterwards.

The third factor is the charring of the barrel. The barrels are burned from the inside until a layer of charcoal develops on the inside. The fire is extinguished with fresh water to prevent the charcoal from burning to ash. This charcoal has an enormous inside surface and is therefore very active to bind with other substances. The charcoal reacts mostly with the sharp and intense tasting compounds from the distillation process of the Bourbon. This charcoal filter does not work forever and will exhaust over the maturation period. After the whisky is entered this layer of charcoal effects the whisky and makes it smoother as well. The warehouse manager talk about subtractive maturation. Read more about it here.

The last factor is closely interlinked with the other influences as it is connected with them. It is the time the Bourbon matures in the cask. The normal Bourbon that is stored in the cask for a few years and does not have an age statement on the bottle, will exhaust the barrel much less than for example an Elija Craigh 18 years old during its enormous maturation period. 

The charred inside of a Makers Mark barrel
The Charred Inside of a Makers Mark Barrel

The Distilling and Barrelling Strength

The barrelling strength of the Bourbon (ABV) is very important for the successive Whisky. Alcohol is a much more better solvent and flavour carrier than water. A Bourbon like the Makers Mark barrels at low ABV and therefore does not exhaust the barrel as fast as a high ABV white dog (raw Whiskey). Who now thinks that Makers Mark has less flavour is mistaken. They don't have to dilute as much at time of bottling which results in a stronger flavour. The higher the ABV of the Bourbon in the cask has been, the less flavour of the toasting and charring is left in the barrel for the later Whisky.

The finished Knob Creek bourbon
The Finished Knob Creek Bourbon

The white dog (raw Whiskey) is colourless. After the Bourbon is being dumped from the barrel it got a golden colour. All the colour comes from the barrel. Some of the colour compounds are still inside the cask and will be transferred to the successive Whisky.

4. Effect on the Colour

5. Whisky Examples

Here we now have examples of Whiskys matured in Ex-Bourbon casks.

This Bowmore Scotch Whisky is mildly peated and has a sweet, creamy caramel character. It was purely matured in Bourbon casks. Link


The Tullibardine Sovereign is a typical Highland Single Malt. You will nose fresh malt and a combination of hay and grass. The taste will give you barley, pears and creamy chocolate. It was matured in first fill Bourbon barrels. Link

Nose: Fresh and floral

Taste: Smooth and soft with Crême Brulée and fresh berries

Finish: Soft sweet and medium long

It was matured in Ex-Bourbon casks. Link