Why Whiskey is Aged and What Effect It Has on the Flavor


Letting the beloved whiskey sit in a barrel for 10 years sounded awful, as it would take a decade before we could take a dram. I remember wondering why they would let it sit for this long. It turns out it is for a very obvious and essential reason!

Why is whiskey aged?

Whiskey is aged to get the familiar color and flavor everyone knows. When the whiskey enters the wooden barrel it is a transparent, moonshine-like spirit. Over the years, flavors and color are absorbed from the wood of the cask into the whiskey. Older whiskeys generally are darker because they have been in the cask longer.

Interestingly, the aging of the whiskey turns out essential to its existence. It is important for you to know what happens during the time the whiskey sits in the cask. Don’t you want to know the different between differently aged whiskeys? The rest of the article will briefly cover all you need to know!

What is aging and why is whiskey aged?

Before being bottled, whiskey remains in a wooden casks for a period of time. This is called aging. During this aging process, the whiskey comes into contact with the wood. Because of the high alcohol concentration, the whiskey is a great solvent. The wood is slowly infusing the whiskey with lignins and chemicals like lactones (buttery flavor), vanillin (obvious) and tannins (also called wood spice, it ads color and dryness to the whiskey).

Temperature fluctuation promotes flavor exchange between whiskey and wood

The whiskey barrels are rarely stored in temperature controlled environments. Instead, they are exposed to outside temperatures. The day and night cycle, as well as the summer and winter temperature shift makes the whiskey expand and forces it into the wood of the barrel. In the colder periods, the wood contracts and pushes the whiskey out back into the cask. There is also a percentage that does not end up back in the cask but evaporates, this is called the “Angels’ Share”.

Charred or toasted barrels filter out unwanted and harsh flavors

The inside of the barrels are often charred or toasted. This charcoal layer will filter out unwanted chemicals and reduce some nasty flavors. They will also induce more of the woody notes to the whiskey. They do not cause the smokey smell and taste of the whisky, as this comes from the peat smoke used to dry the grain with which the whiskey is made.

The longer a whiskey is aged, the more of the harsh flavors are filtered from the whiskey. This makes older whiskeys more smooth and arguably more enjoyable to drink. A 20 yo Scotch will be way smoother that its 10 yo counterpart.

Old wooden barrels and casks at Lafroaig whisky distillery warehouse established in 1815.

The wood induces colors to the whiskey

You can imagine that a whiskey that is aged longer often has a darker color to it. This is noticeable in many whiskeys of brands that have different age variant of the same whiskey. However, color can not guarantee you anything about the age or quality of the whiskey as distilleries often use caramel coloring to artificially color the whiskey. I encourage you to read more about the reason whiskey is brown over on an article I have just recently published.

It is said that between 60% and 70% of the flavor of whiskey comes from the barrel. Before it enters the barrel it looks like vodka: high in alcohol and transparent. It tastes heavily like the malted grain it is made from. There will be none of the color and wood flavors that you know.

There is also a big difference between the first batch of whiskey produced in a cask, versus a later batch that has been produced in the same cask. This is the case because the influence of the wood is biggest with the first batch. You could compare it to a tea bag.

Bourbon whiskey barrels can only be used once, after which they are sold to other distilleries all around the world. Scotland buys a lot of these used bourbon casks as they are allowed to use barrels for multiple batches.

How long is whiskey aged in barrels?

  • Scotch: Minimum of 3 years
  • Bourbon: No minimum age
  • Straight bourbon: Minimum 2 years. If younger than 4 there must be an age statement on the bottle.

Different whiskeys are aged for different periods of time. Scotch whisky by law has to age for a minimum of 3 years for it to be called Scotch. For bourbon there is no minimum age requirement. There is a requirement when you want to call bourbon “Straight bourbon”, which would require you to age the whiskey for a minimum of 2 years. If straight bourbon is aged for less than 4 years, the distillery has to provide an age statement on the bottle.

If you find a straight bourbon without age statement, it has been aged for over 4 years (but probably not much more).

This is the minimum amount of time, but what about the optimal period? This differs per whisk(e)y. For Scotch whiskey the sweet spot typically lies between 10 to 18 years of aging. For bourbon the best point typically is way shorter at roughly 4 to 9 years. This has to do with a couple of factors. First, bourbon has to be aged in a fresh, new, oak wooden cask. The effect of the cask is much bigger when it is new. Next to this it has to do with the climate. Temperature fluctuations speed up the aging process as the spirit is pushed into and forced out of the wood. The moderate Scottish climate does force the whiskey in and out of the wood as quick as the extremely warm to freezing cold temperatures in Kentucky.

This is also the reason why you never see a very old Tequila, as most of it is aged in Mexico.

Exceptions to “regular” aged whiskey

There are always distilleries that go way overboard. The first example are extremely old whiskeys that have been aged for 50 years. Some people would say that older always automatically is better, which is definitively not the case. When the whiskey is very old, it risks tasting like a wet log. The wood influence will be huge, and there will be many tannis that have found their way into the drink, making it very dry.

These old whiskeys are mostly whiskys without the extra e, as they come from Scotland. Examples are the Glenlivit 50yo, the Glenfiddich 50yo, the Balvenie 50yo and there are many more. The bottles go for ridiculous prices ranging from $1000 to up to $25000 a pop. I would be honored to try a glass, as I have never done so before. I will be looking for the wood taste as it will probably not be hard to find, and I will try to find what is left of the other tastes.

The other end of the scale are underage whiskeys. More and more distilleries have started to sell so called White Whiskey, which is whiskey that has been in a barrel for just a couple of days. Within this time, the barrel has had little chance to work its magic and will therefore be nearly impossible to taste. These types of white whiskeys are a way to create a product quickly as it can be made in a matter of days. It might be fun to mix with, but all the harsh tastes that the barrel would filter out are still there. No fun.

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