Wood It Were Simple

Posted by on Mar 9, 2014

Having left off at new make spirit, it’s time to delve into the maturation of whisky and the important role that wood plays in how a whisky comes to be.

Scotch whisky ages for at least three years in oak casks of no more than 700L capacity. There isn’t any specification on the type of oak used: it can be new or used, but distilleries almost always fill used oak casks with their spirit for three main reasons:

1) Used oak is cheaper than new oak.

2) Wood components are extracted more readily and in greater quantity in new oak barrels. Given the lengthy maturation period a new oak cask could simply make even a three year old whisky taste like sawdust.

3) Reusing barrels allows for added nuance and the extraction of additional flavours from whatever residual liquid from the previous fill has impregnated the wood.

Historically, sherry casks were the preferred vessels for maturing whisky in. British sherry importers were bringing casks of sherry into the country literally by the boatload and then dumping the barrels once they’d sold the contents. After regulations on Bourbon were established in the U.S. in the 1930s, however, the Scots found a new supplier, for Bourbons must be matured in new oak casks. As a result, a large number of whiskies are nowadays matured in ex-Bourbon barrels and some distilleries even own the American Oak forests before ‘renting’ the wood to the Bourbon distilleries and subsequently taking it back to use for themselves. Talk about vertical integration.

That being said, sherry barrels are still used consistently, and The Macallan prides itself on almost exclusively using sherry casks. But many distilleries now are also experimenting with all kinds of wood: Port barrels, Madeira barrels, Sauternes, Cabernet, and even beer (Ever wonder why Innis and Gunn was brewed in the first place? To season oak barrels for whisky makers!) Most of these barrels are being used to finish a whisky — that is to say that a whisky spends most of its life in something like an ex-Bourbon barrel before being racked into a Port barrel for a few months before bottling — but all impart unique flavours to a whisky. As a general rule, these are the kind of flavours you might get from some of the more well-known barrels:

-Bourbon: Vanilla, honey, and toffee.

-Sherry: Fruit, especially raisins. Maybe some chocolate.

-Port: Dried fruits and spice.

-Rum: Chocolate, raisin, and vanilla.

The degree and intensity of all of these flavours and aromas are highly dependent on the time, temperature, and environment (which I’ll cover a bit more in later posts) not to mention the quality of individual barrels and that of the new-make spirit. Obviously, something as smokey as an Ardbeg will not display the characteristics of a Bourbon barrel very well. The flavours are also very much dependent on the age of the cask, for Scotch whisky distillers reuse their casks three, maybe even four times. They stop using the cask once it is ‘spent’; that is to say that nearly all of the useful, desired components of the wood have been extracted from the wood and so the cask really has nothing more to add in terms of flavour. Sometimes a cask simply needs to be rejuvinated through stripping the wood and re-charring the newly exposed layer, but there are limits to how much this can be done.

For fear of carrying on too long, I’ll stop it there. There is still a heck of a lot more to be covered on wood, time, and environment, however, so stay tuned for more posts!