Some of the most popular Scotch whisky in the world is matured, solely or in part, in sherry casks. And for good reason—sherry wood can amplify the best in whisky, producing something sweeter, nuttier, and more complex than ex-bourbon casks alone. Yet most of the sherry casks used by the Scotch industry have a secret: they’re not really used to mature sherry wine, at least not in the same way that a whisky cask is used to mature whisky.
To understand why, we need to look to the past. Until relatively recently, it was common for Spanish sherry to be shipped in wooden barrels. Once they arrived at their destination, they were emptied and bottled, and the remaining cask, infused with sherry, was repurposed to hold other things, like whisky.
Then, in 1981, the Spanish government changed its export rules, banning the use of casks for shipping. The global supply of sherry barrels dried up overnight. The sherry industry still uses barrels for maturation, of course, but the solera system used in sherry production doesn’t really generate any extra barrels, since they’re never completely emptied. (Plus, by the time a barrel is retired from a solera, all of the aromatics have been leached from the wood years ago.)
But while the supply of sherry-seasoned barrels may have vanished, consumer taste for sherry barrel-finished whisky did not. So sherry producers began to create barrels specifically for the whisky industry by coopering new American oak casks and briefly rinsing them with sherry for just a few months before transferring that sherry to a traditional solera system. The rinsed barrels are then disassembled and shipped to Scotland, where they are used to mature whiskies like Aberlour and Macallan.
Purists argue that these new sherry-seasoned casks are fundamentally different from the old shipping casks, and the new versions are more likely to generate that meaty, sulphur-y quality that bugs some people about sherry cask whisky. It’s quite possible they’re right. But for most of us, the opportunities to taste whiskies that went into cask before 1981 are few and far between, so that particular distinction remains, for the most part, an academic one.
Editor’s note, 8/25/17: This story was updated to correct a reference to sherry cask producers using European oak. Most sherry seasoned casks for the whisky industry are made from American oak, not European oak.