What Barrels Actually Do: Oxidation, Recombination, Wood Extraction

Use a three-process model to predict maturation behavior and avoid over-aging mistakes that erase front-end character.

Quick summary

Core principle

If we look at what happens inside the barrel, it's basically three processes taking place. And the third one is actually the flavors of the wood, like tea almost, leaching into your new make spirit, leaching into your rum or your whiskey.

So if people think that barrel aging is all about the wood and the color and the stuff, the flavors that actually get extracted from the wood, you'd be wrong. Because the distillate in itself, the new make spirit, actually has a lot of front end and back end flavor that needs to balance out, that needs to become more complex, more enjoyable, more drinkable.

The way that happens is through oxidation and recombination. If we do a distillation run, we cut for heads, hearts, and tails.

There will always be a little bit of heads in your new make spirit. There will always be a little bit of tails in your new make spirit.

There probably should be, because it makes your drink interesting. As a general rule of thumb, what we see is that the headsy smearing that goes into your barrel needs oxidation.

It needs the introduction of oxygen in order to mellow out. So, rough head cut, you actually solve by introducing oxygen.

If there's a lot of tails in your product, you need to barrel age it for a long time. You need to age it for a long time because those headsy molecules oxidize, but the tailsy molecules actually recombine.

They meet and mingle, and every now and then, in such a way that they create a new compound.

How it works in practice

Usually, better in flavor, less harsh. So what we do in a barrel is not just extracting wood flavors. What we do is we allow the drink to actually oxidize.

In a barrel, this goes very well, because a barrel is a breathing, almost living thing. So part of the spirit evaporates. So over the years, you see the level of liquids inside the barrel drop, usually by around three, three and a half percent per year.

As the liquid level drops, more and more oxygen molecules get introduced into the layer of air on top of your drink, inside the barrel. So if you lose some in barrel aging, please know that as a result, you introduce more oxygen. Your headsy factions actually mellow out nicely.

If you leave it in the barrel longer, or if you leave it in the barrel at higher temperatures, maybe you're in a hot climate. We've got a customer in Texas that is like, it's like 35, 40 degrees in summer. You can imagine that recombination goes a lot quicker at those temperatures.

The longer you leave it in the barrel, the more reactions take place, the more interesting the whiskey or rum will become. It stops at a certain moment, and you've reached your full potential. And the problem with oxidation is that oxidation goes quicker than recombination.

Try to buy a fancy whiskey from Scotland will probably do it. Try it and see if there's flavor at the front. There probably isn't because it over-oxidized.

First second that you taste it, you swallow, nothing happens in the front of your mouth. A good indication of over-oxidation. If you leave whiskey in a barrel for 15 years, however many heads you add, it will not create a fruity flavor because they're gone after about five, six, seven years.

Now things get interesting, right? Because if you look at bourbon, it's made on American white oak. And if you look at what the Scots do, they finish their products in sherry casks, in wine casks.

Common mistakes and decisions

So first maybe bourbon barrels, second hand. And then the last two, three years, port barrels, sherry barrels. Weirdly enough, but not so weird if you understand what goes on over here, barrels that actually introduce fruity flavors, sherry and port.

Simply because after 15 or 20 years, this whole first dimension has gone. But if you finish your product on a sherry or a port barrel for two years, you reintroduce porty, sherry-like fruity flavors to bring back up that front end. In other words, you don't need to do that because you don't need to age your whiskey and rum for 15 or 20 years.

I can guarantee you that if it's well cut and well made in a controlled fermentation and controlled distillation environment, after three, four years you'll reach maximum development of flavor. So not yet oxidation or full oxidation and almost perfect recombination. No need to buy sherry casks or those very expensive port casks.

Just buy a cask and have it do its magic. Oxidation, recombination, and finally the wood flavors itself. Now this is a very complicated topic, so I decided to make it slightly less complicated.

If you look at the wood, there's basically two flavors that you get out of it. There's many more, so don't get angry with me, there's many more, but basically there's two. There's the vanillins, a sweet flavor, and there's tannins, a strong, sometimes very harsh flavor, like make tea and leave the bag in for too long and it sort of bites your teeth almost.

Continue with Connects oxidation discussion to missing front-end diagnosis. to build directly on this foundation.

Wood Extraction

Wood extraction is one of three major barrel mechanisms, alongside oxidation and recombination. Extraction contributes compounds such as vanillin, tannin, and toast-derived aromatics that shape structure and finish.

Key Takeaways