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Lesson 07: How do you age whiskey?

Just like I mentioned in the previous lesson, I will only be able to scratch the surface on the topic of whiskey ageing in this specific lesson. I will however, cover some of the more technical details in the lessons that follow this one – such as “Barrel entry proof”, “Angel’s share”, “Devil’s cut” and many more.

If you read the previous lesson, you will know that whiskey is technically whiskey, even before the ageing process has started. The whiskey is clear as water, at this point, since all the color is added to the whiskey by the oak barrels during the ageing process (a.k.a. “maturation”). Although fairly uncommon, it is possible to buy the clear unaged whiskey as I mentioned in the previous lesson – typically marketed as “White Dog“. Also, Corn Whiskey does not have to be aged in oak barrels either – so you can buy completely clear versions of that as well (often sold under the name “Moonshine”).

But for all other whiskey types, you will have to age them in oak barrels to adhere to the law. Technically it can be any kind of oak “container”, but everyone uses barrels (as they are much easier to handle).

Barrels just make so much sense, as a single person can roll them, even though they weigh three or four times as much as that person

And here is how it is done:

  1. Most whiskeys have a high proof/ABV after the distillation process, and since it is illegal to add the newly made clear whiskey to the barrels with a higher proof than 125 (62.5% ABV) you often add water to the whiskey to get to 125 or below. The alcohol strength of the clear whiskey that is added to the barrels is referred to as “barrel entry proof” and I cover this in much more details in lesson 13.
  2. Once the water is blended with the whiskey, the empty barrels are filled at a so-called “filling station” through what is called the “bung hole” in the barrel. This is very similar to putting gas on your car.
  3. Once filled, the bung hole is secured with a plug, typically made from hard rubber.
  4. The barrel is then rolled into the warehouse where it sits for several years, until the whiskey is ready.
Filling station @ Willett Distillery

And that – in all its simplicity – is basically it.

But then again, I haven’t really told you about the most exciting part – and that is how the whiskey gets its color and taste.

The whiskey starts “breathing”

The process of turning the completely clear (and not terribly pleasing) whiskey into that sweet, brown and amazing whiskey we call Bourbon, Rye, etc. is nothing less of a miracle – and a natural one, at that. Here is what happens:

  1. You burn the inside of the barrel until it gets completely charred. This process is called “charring” and I explain more about that (and its cousin “toasting”) in lesson 12. The purpose of the charring is to give the clear whiskey easier access to the natural sugar in the wood, as the charring increases the surface area inside the barrel, amongst other things.
  2. When the charred barrel – now filled with the clear whiskey – is moved to the warehouse, the temperature in the barrel starts rising slowly, as the warehouse is typically much warmer than in the production area, where there is (often) air condition. And when the temperature of any liquid increases, it expands. During the summer months, this obviously escalates.
  3. Since the barrels are filled to the top – and the whiskey is expanding – it is now trying its best to penetrate the wood in an attempt to “escape”. And it is during this interaction with the wood that almost all the flavors are added to the whiskey, as the natural wood sugars are mixed with the clear whiskey.
  4. When the temperature drops again – typically during the winter – the whiskey retracts from the wood again and mingles with the remaining liquid.

Step 3 and 4 now repeats season after season – year after year, and that is how the completely clear whiskey (almost without any taste) turns in that yummy, mouth-watering brown liquid with those amazing notes of vanilla, brown sugar, caramel, etc. etc.

The color of the whiskey turns from completely clear to brown purely by interacting with the wood and the char.

Isn’t nature just amazing?

And that concludes this lesson.

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