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What Is So Special About Mizunara Oak?

Updated: Mar 2

Mizunara Japanese Oak

Original Image by Edinburgh Whisky Academy

Mizunara. Just the word can instantly make a whisky highly sought after. But what exactly is it, and what makes it so special? We wanted to dig into the subject and would like to invite our readers to join us on this journey of discovery.

Let's start digging.


What is Mizunara?

The Mizunara tree, also called the Japanese Oak, is a subspecies of the Mongolian oak (Quercus Mongolica) and is scientifically known as Quercus Crispula. The tree only grows in Japan, and the name Mizunara translates to 'Water Oak' due to its large pores, which makes it prone to leaking. Compared to other oak species commonly used for making casks, Mizunara has fewer tyloses, which are the balloon-like swellings that fill the vertically running vessels of a tree. Additionally, the trees do not grow straight in their native mountainous surroundings, which adds to the difficulty of working with it.

The Japanese whisky industry began using native wood to make their barrels at the end of World War II, due to the difficulties of obtaining European or American wood, among other imported items. Although whisky production was not essential, it was highly popular among the Japanese people and soldiers, so the need had to be met.

Japan has various oak species, including evergreen and seasonal leafy types. The Crispula variety, which has broad leaves and prefers cold weather, was chosen for its similarities to previously used cask woods and, therefore, the best choice for making whisky barrels that would stay true to tradition. The tree is common in deciduous forests in Japan, but due to the characteristics influenced by climate, Hokkaido is considered the best place to grow Mizunara.

Mizunara Japanese oak Quercus Crispula details

Image combined by The Whisky Ardvark - A. Quercus Crispula tree/ B. Summer leaves/ C. Bark / D. Pores close-up/ E. Autumn leaves

Oak has been used to mature whisky since the 1800s, although it has been used to mature wine since the time of the Roman Empire. Nowadays, many countries have regulatory guidelines that require the use of oak barrels. Although the new Japanese whisky guidelines, which will come into effect on March 31, 2024, do not require oak wood, the Japanese whisky industry has been influenced by Scottish whisky standards and has preferred to use oak since the first whiskies were made in Japan in the 1920s. It is believed that the wood plays a significant role in imparting flavour to whisky, accounting for 60 to 80% of its taste.


Sourcing Mizunara Oak

Sourcing a relatively common oak tree from the forest might seem easy. However, this is not the case regarding Mizunara, the world's most elusive oak for casks.

Mizunara is best grown in mountainous forests, which means the tree rarely grows straight, and can reach the maximum height of 35 meters. To ensure the best quality, producers like Suntory only buy logs of Mizunara with a minimum diameter of 70cm, while Chichibu prefers logs between 40 and 60cm in diameter. Moreover, it takes 200 to 500 years for the oak to mature enough to be suitable for whisky casks.

Whisky producers and coopers who wish to make casks from scratch can find quality wood in Asahikawa, Hokkaido. It is home to Japan's largest hardwood log auction, which offers Mizunara logs for bidding between December and March. The auction is conducted through a blind bidding system, where bids are placed before the item is called, and the winner is announced 15 seconds after the item is announced. Needless to say, the offers increase throughout the day, and big companies with a lot of money usually win most of the logs.

Mizunara is sought after by whisky makers and high-end furniture makers who are only looking for the best without room to compromise. They all compete for the same logs without wood defects - tight-grained and as straight as possible.

Ichiro Akuto Chichibu with Mizunara oak logs

Image by - Ichiro Akuto with his priced logs of Mizunara

Many whisky makers prefer to buy ready-to-use Mizunara casks directly from coopers at a hefty price that can rise to more than $6,000 (£4,780) per cask - around 10 times more than an average cost of a barrel. However, the number of coopers that cater to multiple companies has dropped over the years. One cooperage, formerly located in the village of Hanyu and called Maruesu Cooperage, closed in the summer of 2013 when the owner and master cooper, Mitsuo Saito, retired. Fortunately, Ichiro Akuto bought all the equipment from the master cooper and set up a cooperage at Chichibu Distillery.

Another company that used to sell its casks to others was independent Nikka Cooperage, which eventually became a part of The Nikka Whisky Distilling Co. in 2010. After the merger, the cooperage no longer sold its casks to competitors.


Working With Mizunara

The coopers must wait several years for the oak staves to air dry before making casks. Unlike other oak types, Mizunara oak is very porous and needs to be split into logs instead of sawn. To successfully make watertight barrels, the oak must be divided into specific planes, following the vessels running through the wood. Skipping this step will result in leaking casks.

Mizunara oak Quercus Crispula coopering

Images by Ariake Cooperage - Making Mizunara casks

The tree's shape also makes it challenging to work with as it grows with a fluid curvature. The oak is soft, making it hard to shape and further complicated by the high moisture content compared to other oak types. During transportation, the soft wood is also prone to damage.

Learning to make Mizunara casks can be a challenge for many coopers. For instance, when Chichibu made its first two Mizunara casks, neither could hold the liquid inside. They could only get one usable watertight cask by rearranging the staves. It can be an expensive experiment if only half of the barrels made are usable, if that.

To tackle the leaking issue, some coopers in Japan paint the outside of their Mizunara casks with kakishibu, a fermented tannin juice of unripe, astringent persimmons. This practice, however, is avoided by some small whisky producers due to possible effects on maturation and the spirit itself.


What Mizunara Brings To The Table?

But why use oak, which many describe as a nightmare to work with?

Well, for a while, they didn't. When Mizunara was first used in whisky, the spirit was aged for only around two years in casks. The result was harsh and not easy on the palate. So when imported oaks became available after the war, Japanese oak was considered inferior to American and European white oaks until studies were conducted on extended maturation and finishing. Now, Mizunara oak is regarded as the finest vessel for maturing whisky.

Mizunara oak has a distinct sweet and spicy flavour profile attributed to the oak lactones ratio and high level of vanilla. The aromas of kara - an oriental incense - sandalwood, and coconut are evoked from the Japanese oak. Ichiro Akuto, who fell in love with the oak's unique mixture of aromas and flavours, had his washbacks, initially six and now eight, made out of Mizunara when he started building his distillery in 2007 - the first time in the whisky world. He also started filling new make into Mizunara casks whenever he could.

The aromas and flavours developed during the maturation process are so captivating that many whisky producers are willing to put in the effort. Some have also planted new trees to continue the legacy.

Kaiyo whisky Japanese Mizunara oak flavour profile wheel

Image by Kaiyo Whisky

According to legend, when a Mizunara oak cask has reached the end of its useful life, having served its time in maturing whisky, it is ceremoniously retired. It suggests that whisky producers place a high value on these casks. While we could not verify the truth of this legend, it is a pleasant thought to consider.


Mizunara Aged Whiskies

The Mizunara oak has become a highly sought-after for whisky makers worldwide, not just in Japan. Finishing spirits in Mizunara casks from Ireland and Scotland to France and the US has become a trend for those who have managed to get their hand on it.

Many believe that to get the best out of Japanese oak, the spirit must spend a considerable amount of time in the cask. However, some find it troubling that there are allegedly whiskies on the market labelled 'finished in Mizunara oak casks' that have spent only a few months in the wood. If this is the case, the phrase can be misleading and feel like a gimmick to sell the product rather than a genuine contributor to the final taste. Some companies have yet to reveal how long their whisky is spent in Mizunara, creating more mystery around the product.

Beam Suntory is one of the biggest spirits companies that use Mizunara oak to mature a portion of its whiskies. The company reintroduced its Japanese oak program in 2000 after a hiatus of 40 years, during which it had been using refill casks. Mizunara oak has been crucial in producing Yamazaki and Hibiki whiskies for the Japanese market for years. More recently, it has also been used in the makeup of exported whiskies. Beam Suntory has even shared some of its prized barrels with Bowmore, the company's distillery in Scotland.

While other new Japanese whisky producers, such as Matsui Whisky and Shinobu Distillery, use Japanese oak, Kaiyo has dedicated its entire line to whiskies that are fully matured or finished in Mizunara oak.

Here are some released whiskies that have been matured fully or partially in Mizunara oak:

Mizunara oak aged whiskies
Mizunara oak aged whiskies
Mizunara oak aged whiskies

Images by The Whisky Ardvark


Other Types Of Oak Used In Whisky

Quercus Alba

American White Oak - Most common in the whisky/whiskey industry due to its availability

Quercus Robur

European Oak, AKA Pedunculated Oak - Mainly used to make sherry casks in Spain

Quercus Garryana

Oregon Oak - Pioneered in the use of maturing whisky by Westland distillery

Quercus Petraea

European Oak, AKA Sessile Oak - A species of oak tree native to most of Europe. It is the national tree of Ireland.

Example, French oak from Limousin forest - Used in Cognac


Thank you for reading The Whisky Ardvark. Make sure to check out some of our other informative articles, and stay tuned for more.

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