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What Is a Mizunara Oak Cask, and Why Is Every Distillery Obsessed With It?

Japanese Mizunara oak is the latest must-have material for whiskey-aging casks. Here's why.

female taster looking at the colour of whisky in glass at whisky distillery
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What came first, the whiskey or the cask? The cask, of course.

Whether you call it whiskey or whisky, the cask is responsible for the flavor, color and texture of any aged spirit. One cask that has seen a surge of popularity lately comes from a tree called mizunara. So what exactly is mizunara, and why does it seem like every whiskey is spending some time in its casks? We asked a bunch of whiskey experts to find out.

Why Are Casks Important to Whiskey?

When distillation occurs, the liquid left behind is a clear alcohol called ethanol. Ethanol is then aged in charred casks for months – or even years — until the desired flavor profile is achieved.

The art of coopering — or harvesting, assembling and charring barrels — can be traced to various European societies for at least the past 2,000 years and relies heavily on indigenous white oak. Oak’s unique cellular structure and low porosity make the hardwood easy to cut into straight beams, which can then easily be shaped and assembled into a watertight barrel.

"White oak, when properly sourced, seasoned and heated, provides a range of natural color, aroma, flavor and mouthfeel compounds that help define our whiskey," Chris Morris, master distiller of Woodford Reserve, explains. "Plus, its porosity allows for a series of flavor formations to occur due to the spirit's reaction to oxygen."

These barrels, like grapes, contain tannins and other flavor imparting components. While tannins are well known for influencing flavor in wine they are lesser known for their part in whiskey. But in charred oak they are responsible for the emergence of many flavors like vanilla and coconut. French oak is slightly denser resulting in a higher, silkier tannin profile than American oak. One very rare and special type of white oak, mizunara, has the lowest level of tannins of all.

What Is Mizunara Oak?

“Mizunara is a native Japanese oak from Hokkaido,” Gary McLoughlin, founder and marketing director at the Irish Glendalough Distillery, says. "We believe [it's] the world’s most flavorful oak.”

"We believe [it's] the world’s most flavorful oak.”

Unlike white oak, mizunara’s branches and base are slimmer and twisted, reflecting a more complex cellular structure with fewer, long straight planks fit for barrels. The wood itself is more porous and waterlogged (mizu-nara translates to “water-oak”) and requires at least three years of drying time before the slats can be assembled into a cask.

Mizunara is known for bringing a unique and distinct flavor, namely sandalwood and coconut. Whiskeys aged in mizunara casks have a honey-like sweetness to them, as well as a notable light body.

What Makes Mizunara Oak Casks Special?

The scarcity of mizunara is a factor in why so many distilleries want casks made of the wood.

“Each tree must come to an age of 200 years before it can be harvested for use in a cask barrel," Selwyn Chan says. Chan, one of the restauranters behind Nakaji, which which Pete Wells of The New York Times says has “the most exhaustive collection of Japanese whiskey in the city," carries as many fine and rare expressions as possible in his bar — which usually means mizunara is involved.

For a whiskey to fully reap the benefits of aging in mizunara casks, Chan says it should sit for at least 20 years, which adds to the rarity (and high price tag) of whiskeys that maximize mizunara's potential.

“[Mizunara’s] structure, and therefore its wood chemistry, is different from American oak, which means that it imparts different aromas to the spirit than American oak does," Stephanie Macleod, master distiller of Dewar’s, says.

Her recently released Dewar’s Japanese Smooth is her first foray into the mizunara game.

“For Dewar’s Japanese Smooth, this mizunara finish enhances the signature Dewar’s heathery floral honeyed notes whilst subtlety imparting complex woody notes of sandalwood and cinnamon spice,” Macleod says about mizunara's flavorful virtues.

Now, while it’s no secret that many rare whiskeys exist, some of the most sought after are those that spend time in a mizunara cask.

Suntory is the most well known producer but plenty of big players are getting into the game. Glendalough and Chivas Regal are two distilleries that have done it well, releasing Glendalough's 7 Year Old Mizunara Cask and Chivas Regal Mizunara Special Edition, respectively. Standard & Strange and Golden Gate Whisky collaborated to create a cask-strength version. Even ASAP Rocky's new Canadian whisky claims influence from mizunara casks. Prices vary greatly but begin in the $50 range, going as high as the thousands for something like Yamazaki 18 Year Old.

The History of Mizunara Oak Casks — And Their Future

This particular wood has only been used in casks for the past 100 or so years. After World War Two, the presence of U.S. troops in Japan led to a greater demand for aged western spirits. With limited access to supplies, and no access to white oak, even the local soggy oak trees seemed like the best option. The smooth taste and nuanced appeal were just a happy coincidence.

“The trunks of these uniquely beautiful trees are prone to growing twisted," McLoughlin says. "It then takes three years to dry, and even then, is notoriously difficult to cooper due to its porousness. However, therein lies its saving grace: Whiskey can seep deeper into the wood.”

But with mizunara's popularity and rarity comes competition.

“To acquire a mizunara cask, you must blind bid against the giants of Japanese whiskey on one day per year to get your year’s supply," McLoughlin says. "We were the first Irishmen to show up in the only independent cooperage in Japan and we developed a close relationship with the people there.”

Mizunara takes 200 years to grow, so with supply far below demand, the future of mizunara casks relies on sustainable harvesting methods. McLoughlin explains that up to seven mizunara saplings are planted for every tree felled. By utilizing a sustainable management of forests, called continuous cover forestry, no area of mizunara trees are clear felled, or completely razed. Instead areas are thinned out to allow the replanting of saplings to support the health of the forest for future generations.

So once the requisite 200 years, or more, has passed, how does McLoughlin suggest imbibing? “An elevated highball or pairing with seafood dishes such as scallops, salmon and sushi," he says.

Stephanie Macleod insists that “the best possible way to indulge in Dewar’s Japanese Smooth is over a large cube of ice. The small fraction of water opens the spirit to allow notes of sandalwood and cinnamon to push through.

Selwyn Chan cautions buyers to beware. Read the label carefully and beware of expressions that he says “don't garner the full benefits of the mizunara cask due to short maturation periods. [Mizunara] could effectively become more of a marketing term.”

His advice on how to drink is far more straightforward:

“In order to enjoy the full flavor profile offered from a mizunara cask-aged whisky, I would recommend a neat pour.”

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