Why Is Everyone Suddenly Aging Spirits in These Japanese Oak Barrels?

Mizunara oak, a type of wood native to Japan, is knotty, slim, and brittle. It’s also a current obsession amongst whiskey lovers and distillers alike.

Bourbon and Scotch whisky makers have long been converts to the incredibly hard-to-work-with — and even tougher to obtain — Japanese oak. But now, rum, tequila, and even gin makers have begun to age their spirits inside barrels built from these regional staves. But why has everyone become so enamored with these casks?

What makes mizunara oak so special?

“The trees are very rare and, uniquely, cannot be cut and used for casks until they are about 200 years old, so sourcing the wood is particularly expensive,” says James Bowker, House of Suntory's global advocacy manager. 

“The branches of the wood itself are also slimmer and rarely grow in straight boughs, which makes them more difficult to cut into casks,” says Bowker. “Mizunara has a tendency to warp and crack during maturation, making it highly challenging to work with.”

Dan Crowell, the U.S. Glenmorangie brand ambassador, emphasizes that competition for the wood is also fierce. “Mizunara logging is highly regulated by the Japanese government to protect against deforestation,” he says. “Mizunara logs are sold via auction and are in high demand by furniture makers as well as whiskey producers, driving the price of acquisition up.”

Why is mizunara oak so difficult to work with?

The reason why this oak is so difficult to work with comes down to its composition. Mizunara, which translates to “water oak,” is incredibly porous and has the ability to absorb a lot of liquid, which increases the length of the seasoning period for spirits. 

“Tyloses formation [the bubble-like outgrowths that form in the tissue of wood that help prevent water from passing through], is crucial to creating a watertight cask, [and] is much lower with mizunara than with oak species more typically utilized for cooperage,” says Crowell. “As a result, and due to its irregularly aligned growth patterns, mizunara can’t be sawn for cooperage and must be hand-split along the existing grain structure to avoid creating even more leakage potential.”

Single casks made from mizunara oak can cost $5,000 to $6,000, or even more, due to the complexities of working with the wood. And they can take years to purchase.

“A cask as such is not just bought,” says Julian Langestraat, global brand ambassador to gin brand Monkey 47. “After starting our effort to acquire the ‘holy grail’ of aging barrels back in 2016, and spending two years pleading our case, we finally secured the right to purchase five of these prized vessels.”

How does mizunara oak impact spirits?

Despite its difficult-to-work-with nature, mizunara oak uniquely impacts the spirits that mature within it. The wood is known for imparting “wonderful incense aromas like sandalwood and cedar, rich coconut notes and soft spices,” says Bowker referring to its impact on Suntory whiskeys. “It provides unique Japanese character and elegance, a natural addition to the strong Japanese roots of these Yamazaki whiskies.”

Langestraat says that similar notes emerged when Monkey 47 used the oak to mature its Distiller’s Cut 2020, calling it “a soft, elegant dry gin with a refined top note of sandalwood and a touch of coconut that combine to offer a supple sensory experience.” 

Crowell notes that “mizunara is also capable of producing mature spirits with flavor and aroma characteristics highly complementary to Japanese cuisine.”

Still, it takes a skilled hand to work with the oak and many suggest it’s important for spirits to spend years aging in the barrels before they impart the optimal flavors. 

Dr. Bill Lumsden, head of distilling and whisky creation at The Glenmorangie Company, recalls the first time he ever tried a whiskey with this special oak. “I first tasted Japanese whisky from mizunara oak casks many years ago and, while I didn’t immediately totally enjoy the flavor profile, I was deeply intrigued by it, and in particular how different it was from American or European oak,” he says.

Lumsden worked with the oak for Glenmorangie’s A Tale of Tokyo release. “It gave me a bit of a challenge as I had to ensure that the powerful flavor impact of the mizunara oak did not dominate over the whole taste profile, and instead created a beautiful and delicately balanced whisky,” he says.

While there’s no doubt that working with mizunara for longer allows it to impart more flavors, it remains a challenge. 

“Mizunara has a relatively low tannin content which can be favorable when maturing whiskies for an extended period, but the leakage risk is ever-present, making extended maturation in mizunara a promising but risky proposition,” says Crowell.

Still, for Suntory, Bowker sees it as the only option, “When using mizunara casks, it takes a long time to extract the true flavor of the oak, so the longer the whisky is aged in the barrel the better as the whiskies seep deeper into the casks and develop richer flavors and aromas.”

It’s the hard-to-find aromas and flavors that mizunara adds to whiskeys, gin, tequila, and any other spirit that works with the oak that make it unique, allowing it to play particularly well with various cuisines and a joy to imbibe on any occasion.