Why Do Distillers Use Oak Casks to Age Whisky? It's Not Just Rules (How to Whisky)

When you grab a whisky off the shelf, chances are it’s a spirit that’s spent time in an oak cask. And that’s no coincidence. Ever wonder why whisky matures in oak barrels? We’ll tell you why.

The world is full of different trees, and in theory, any of them could be turned into a cask. So why oak, you might ask. There are plenty of good reasons.

Oak is one of the most common trees in the world. Its wood is sturdy and just porous enough to allow a spirit to mature without leaking easily.

On top of that, oak imparts a lot of flavor. That makes it ideal for aging spirits. There are also more than 600 different species of oak, each lending its own character. Plenty of variety to play with.

Another reason oak is used comes down to regulation. Some countries, like Scotland and the United States, have strict rules around the use of casks.

In the United States, for example, bourbon must be aged in new oak barrels. Those barrels have to be charred on the inside before the White Dog, the new-make spirit, goes in.

Once the bourbon is emptied, those casks can’t be used again for bourbon. That creates a vibrant trade in American oak barrels, something Scottish, Irish, and other whisky makers around the world are more than happy to take advantage of.

In Scotland, the rule is that only oak may be used, whether new or used. In the latter case, there are additional conditions regarding what the cask previously held. Tequila, beer, wine, and sherry are allowed, for instance, but cider is not.

Not every country uses oak exclusively. While Scotland and the U.S. regulate casks, Ireland does not in the same way. Irish whiskey must mature in wood, but that could be chestnut or another species.

In parts of Asia, such as India, Taiwan, and Japan, acacia, cedar, or cherry wood may also be used to make casks for whisky maturation. The drawback is that these woods are generally more porous and often harder to cooper into reliable barrels.

So you’re more likely to see a whisky finished in cherry or cedar than a long-aged whisky matured entirely in those types of casks.

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