Everyone has a preference when it comes to two of the most popular national spirits, bourbon and scotch. But these two national whiskies often come from the same casks: literally! Millions of used bourbon casks have made their way from America to Scotland, been refilled with their whisky cousin and left to age for another decade or two. So it’s theoretically possible that if you tasted an older bourbon next to a newer scotch you could be drinking from the same cask! But more than interesting trivia, the laws and tastes that led to this practice have brought about substantial flavor profile shifts for both spirits. So how did we end up here?
Like most things to do with whisk(e)y, the answer begins with trees. Kentucky and the surrounding states are covered in dense forests filled with old oak trees. Despite some foolish logging practices in past centuries, there are still plenty of trees of exceptional size and quality. So new oak casks are easy and cheap to come by. Across the Atlantic, the great forests of Britain were felled centuries ago to craft the British navy and merchant fleet that sailed the globe making a mess of things. So if the Scots wanted inexpensive casks for their spirits, they had to go somewhere else. Enter: the English aristocracy absolutely sloshed on sherry.
Sherry became incredibly popular with the English in the 1800s. So popular that the Spanish sent ship after ship loaded with great big sherry casks that would be unloaded at English ports, the wine inside bottled, and the casks left sitting around the docks. The enterprising Scots picked these up for a song and carted them back to the Highlands where their whisky began to pick up those rich, fruity, and dark sherry notes. So when do bourbon casks come in the picture? Hold on, we’re getting there.
Historically, the corn whiskey made in the American southeast was not all aged in new oak. Plenty of it was drunk unaged as moonshine. Plenty more ended up in used barrels of varying quality. So why the shift to only new oak? Well, you’ll find stories about whiskey floated in barrels down the Kentucky river, into the Ohio, on down the Mississippi where it was finally unloaded in New Orleans somewhere around Bourbon Street where the consumption of whiskey has never slowed (whether the street gave its name to the spirit or the spirit gave its name to the street is a whole other tangle of myth we can’t untie now). The story goes that this spirit aged quickly on it’s way to the Big Easy, bouncing along in the sun. And since the barrels weren’t floated back upstream, the practice of filling new oak and the taste for sweet and oaky whiskey both took root. That’s possible but it’s more likely that the big bourbon corporations springing up in the late 19th century had a bit more to do with it. Barrels were cheap and flavor could be imbued quickly and consistently with new ones. Of course, none of that mattered once prohibition hit.
But prohibition wasn’t a death sentence for the bourbon kingdom (apologies to Louis XVI) and when it came limping back to life in the thirties, one little word snuck into a 1935 federal law sealed bourbon’s fate: “new.” From that point on, all bourbon had to be aged in new, charred oak vessels. How did the government come to this decision? Well it may have been history or flavor or consistency. But it also may have had a lot to do with major logging industry lobbying and a little help from an Arkansas congressman whose state’s timber barons stood to benefit a lot from the requirement. Either way, the practice was now law.
As bourbon became more popular and more and more casks were emptied, a problem became quickly apparent: what do you do with thousands and thousands of barrels that you can’t refill? At first, most of them were just trashed. Some ended up as mulch or flooring. But, after WWII, as shipping became cheaper and the scotch industry limped back to life a solution was found. The English taste for sherry had died off so those casks were more expensive and harder to come by, especially as the Spanish began to bottle their own sherry instead of shipping whole casks. On the other hand, bourbon distilleries were practically giving away their towering excess of barrels. Slowly, Scottish distilleries which were in the process of increasing production began to import bourbon casks and, slowly, the profile of scotch began to change.
Not only are bourbon casks imparted with different alcohol flavors (whiskey instead of wine) they are made from different trees. Instead of the dense spice notes of French oak (the species used in most sherry casks), the bourbon casks came with much more vanilla from American oak. It’s difficult to pin down the source or every flavor note but, in general, sherry aged scotch will have notes of dark fruits, nuts, wine, and a forest floor funkiness. Scotch from bourbon casks will have much more vanilla and caramel as well as a lighter sweetness.
This shift in profile happened slowly but is now pretty well entrenched. Popular blended scotch helped cement the public’s taste for this change. Now, there are a few sherry holdouts such as Dalmore and Macallan. And a few distilleries such as Glendronach have switched back. And plenty of distilleries have special releases finished in sherry but these are the exceptions and the vast majority of scotch is aged in ex-bourbon casks. That shift wasn’t driven by distillers carefully selecting vessels for flavor but by the quirks of various laws and tastes and trade agreements.
Incredibly, millions of bourbon casks have made their way from the forests of the American southeast, through Kentucky’s vast rickhouses, and across the Atlantic to rest in the dunnage houses of Scotland. So the next time you pick up a strong vanilla note in a glass of scotch, you can thank the forests of two continents, the English navy, the winemakers of Spain, a crafty congressman, and that glass of bourbon you might drink next.
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