Barrel-aging spirits. How does it work?

Barrel-aging spirits. How does it work?

All oak and iron bound

We currently have around 60 casks at Empirical from around the world; ex-Bourbon, ex-Cognac, ex-Bordeaux, Amburana, you name it. And the family is growing. 

To celebrate the restocking of our Ehime series Cask 02 and Cask 03, we thought it was time to have a look at what happens inside our precious barrels. 

Yes, gird your loins, we are about to get slightly nerdy about oak.  

Crafted by the Celtic tribes of Northern Europe over 2000 years ago, barrels have ensured liquids could be shared and transported throughout history. The delicious flavor nuances they imparted were just the cherry on top of the cake, really. 

And every barrel has its very own fingerprint and personality, making it even more exciting to taste and discover each of them. But how does it work?

The Magic of Wood

How do wood and time turn all they touch into delectable golden nectars, you may ask? Well, these chemical reactions can be narrowed down to three magic processes: extraction, oxidation, and concentration.
Extraction is the first occurring transformation and the most straightforward one.

In contact with the liquid it holds, flavor compounds that are naturally present in the wood and through charring are transferred to the spirit, like vanillin (vanilla), oak lactones (peach, coconut), eugenol (clove), and tannins that are familiar. Although these flavor extractions keep on occurring throughout the maturation process, most of them would show up within the first year. 


Onto the second process. Barrels are porous and quite literally breathe. The organic compounds present in the wood and in the spirit react with one another in contact with oxygen, breaking them down and creating new delicious flavor molecules. The result is increased fruity and spicy notes for a smooth and comforting sip. 

And just as any liquid left out in the air evaporates, the same process occurs inside a barrel. Both ethanol and water evaporate over time, sometimes amounting to up to 12% of the full volume a year, concentrating all the flavors left in the spirit.

Temperature and humidity have a major impact on the whole process. The drier the climate is, the more water will evaporate and quite logically the more humid the environment, the more ethanol will leave, producing different ABVs of the final product. Temperature on the other hand can dictate the length of maturation. When alcohol warms up, it expands, which means the liquid is further pushed into the wood and penetrates it for extra flavor extraction. This takes longer and sees more fluctuations the colder the weather is.

About Bourbon

Here’s some bonus content; a few facts about Bourbon that will make you shine at the next dinner party.

Most of the barrels used around the world are Bourbon barrels. Why? Because of rules. Bourbon can only be called such if they are aged in new American oak barrels. This means that when they are used once, they cannot make Bourbon anymore. 

And you know what we do with rules at Empirical? We disregard them, which is why we are the lucky owners of quite a few of them, each bringing their unique identity to our koji-based Ehime series. 

Want to taste the magic of wood and time, and the distinctive flavor nuances each cask brings to our spirit? You know what to do. Get your Ehime Cask 02 and 03 and indulge.

Shop EHIME Cask02

Shop EHIME Cask03

Back to blog