An experimental revolution is underway in Ireland, with whiskey producers taking advantage of regulatory flexibility in the maturation of Irish whiskey. Unlike bourbon or Scotch, Irish whiskey doesn’t call for any specific type or treatment of wood and allows for any type of finishing barrel, including other spirits, wine, and beer. With scores of new Irish whiskeys hitting the market, exploring the grand possibilities that such flexibility enables is increasingly becoming a way to distinguish one brand from another.

“It’s all built on the idea that Irish whiskey is unique in the sense that it allows for all wood, not just oak, in terms of legislation,” says Alex Chasko, Teeling Whiskey’s master distiller. As Ireland endured pandemic-related shutdowns, Teeling released a series of single casks in order to continue connecting with consumers at home, with barrel types including Brazilian amburana, cherrywood, chestnut, and Hungarian oak. Next came the first full release in the distillery’s Wonders of Wood series, a single pot still whiskey distilled in 2015 and matured in virgin barrels made with Chinkapin, a type of North American oak.

“The Chinkapin oak gives us a level of spice and tannins that is not normally associated with American oak,” Chasko says, “There is also a distinct coffee and dark chocolate, earthy note that we get from the casks. … For me, it is this middle ground between American and European oak, with a level of spice that fits in nicely with the natural spice that we get from the 50-50 mashbill of malted and unmalted barley.”

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At Waterford Whisky, after a years-long wait exacerbated by the pandemic, the distillery was finally able to import a shipment of Andean oak casks. “These have a tighter grain than American oak but not as tight as European [casks],” says Ned Gahan, Waterford’s head distiller.

Waterford has just begun to analyze the flavors that the Quercus humboldtii casks sourced from Colombia may produce, but early returns have been promising, with a range of floral and spicy notes flecked with grapefruit and other citrus. “There’s a bit more [chemically] on the volatile phenol side, such as guaiacol and eugenol, which give spicy and smoky notes,” Gahan says. The casks also feature reduced levels of lactones, which produce flavors such as vanilla and cocoa.

“This was good enough to ask for 210 barrels of,” Gahan says. Waterford plans to use five barrels as an additional component to play with across each of its single-farm, single-barley variety distillation runs — adding a new variable to the mix of bourbon, wine, and virgin barrels the distillery already uses — and aims to continue acquiring more of the barrels in the future. “We’re not doing something just for the sake of it, though,” he notes. “We’re looking for the best oak and the best barrels.”

Certain distillers see the very nature of Irish whiskey as being fundamental to the success of using such a sweeping range of cask types. “Because triple-distilled Irish whiskey is more delicate, you’re actually allowing the wood to influence it more,” says Denis O’Flynn, a partner in Clonakilty Distillery.

“It’s one of the reasons I think Irish whiskey as a category is at the forefront of experimenting with different types of wood right now,” adds Michael Scully, Clonakilty’s founder. The distillery has released well over a dozen brewery collaborations, working with both American and Irish breweries across all manners of beer casks, including barleywine.

One of Clonakilty’s most intriguing limited editions may be the single-cask Rivesaltes Finish, which makes use of the oft-overlooked wine as opposed to the whiskey world’s typical choices of sherry or port. The fortified dessert wine imparts an intense flavor to the whiskey, with golden sultanas and syrupy sweetness that manage to smooth out the edges of a bottling at an otherwise booming 57.7 percent ABV. “This one just bursts on the nose,” O’Flynn says.

“The stronger flavors, we find, work really well with our spirit, and we are the first Irish distillery to do anything with Rivesaltes casks,” he says.

Elsewhere across Ireland, distilleries old and new are continuing to deploy a range of inventive cask types. Bushmills first released its Distillery Exclusive acacia wood whiskey in 2018, maturing single malt in the barrels for a decade. At Roe & Co., the distillery makes use of Japanese sugi for a release of the same name. It’s produced with an inventive finishing process, with a handful of barrel-length rods of the Japanese cedarwood inserted into 10 casks, offering wispy smoke and incense notes, along with floral aromas and wood spice. The porous wood, with a fraction of the density of oak, rapidly imparts its flavors into the whiskey.

Back at Teeling, where its warehouses have a smattering of roughly 150 different cask types across all shapes, sizes, types of wood, and previous uses, exploring these possibilities is an ideal path for continuing to derive exciting and new flavors within whiskey. “I look at whiskey like a chain — the batch of grain going through the mill, that’s the first link in the chain,” Chasko says. “Maturing and then finishing a whiskey is putting the last link in the chain, and you’re trying to put the best link in each step.”