Mizunara oak whisky casks

Mizunara oak (Quercus crispula) is not the obvious choice for whisky making and maturation. Mizunara oak is rare and expensive to obtain, it grows twisted so is difficult to cut into staves and being both wet and soft is an ordeal for the cooper. If that was not enough the casks have a tendency to leak. Despite all this, whisky producers in Japan are enthusiastic about it, and the wood is starting to attract attention around the world due to its unique flavour profile.

A break from tradition

Japanese distillers have remained true to the Scottish whisky making tradition from the very beginning in 1923. It has been argued, not unfairly, that the Japanese are making whisky more traditionally than many Scottish distilleries today. A key difference is emerging however, which has now become established in Japan. The adoption of Mizunara oak barrels for the maturation of whisky is far from a universal practice, and in most cases these are being used for finishing rather than full maturation. It does offer Japanese distilleries an advantage that is only available to the Scots and other competitors to a very limited extent. However the adoption of Mizunara was anything but deliberate.

The history of Mizunara casks: born of necessity

The time of the Second World War was for many countries, including Japan, an extremely difficult one. During the last phase of the war, Japan had practically no more access to imports. This starved Japanese distilleries access to European or American casks for whisky maturation. Although the production of whisky was not a priority, it had become the main drink of the Japanese Army. Demand thus rose sharply during this time.

Consequently Japanese coopers and whisky makers sought and found a domestic alternative in the form of oak. Mizunara oak (Quercus crispula) which had previously only used to manufacture of luxury furniture was the obvious choice.

At first glance only disadvantages

The use of Mizunara oak, a variant of the species Quercus Mongolica, for whisky barrels was not immediately recognised as a stroke of luck. For although it contains a lot of flavour carrying tannins and lignins the wood it tends to overpower whisky on first use. The tree also grows crookedly, features a high concentration of knots, lacks waterproofing oil enzymes and carries a lot of moisture. All of which means staves construction is more laborious and wasteful, it’s neccesary to cut along the grain to minimise the all but inevitable leaking.

An overpowering palate

Mizunara is not only a challenge for the cooper however but also one for the whisky drinker, at least to begin with. In the early stages of maturation, the Mizunara oak tends to give the whisky a very intense, astringent woodiness due to its high tannin content, which causes the oral mucosa to contract. Given the Japanese preference for light, sweet and gentle spirit it’s easy to understand why this did not catch on quickly.

Japanese blenders viewed the local Mizunara oak as a inferior alternative to American and European oak, due to the cask dominance on aroma and taste. This perception continued for many years after the war. The Japanese whisky manufacturers and blenders did not realise that Mizunara wood takes more time to develop the desirable whisky flavours.

Redemption of Mizunara casks

Unfortunately as cask maturations were far shorter during the war the whiskies were bottled young without sufficient time to develop. It was later discovered that for the true character of Mizunara to develop, around two decades of maturation are necessary.

The fine aromas only develop after a long period of storage, or as a finishing. When ready the whiskies shows a unique sweet and spicy taste profile, which is due to the lactone ratio and the high vanilla content of the oak. Aromas derived from the Mizunara oak are of Kara (a type of oriental incense), sandalwood and coconut.

The challenge of Mizunara Casks

As a rule, Mizunara oak is made in Japan as the 500 litre puncheons and the associated costs are substantial. Even if the circa $6,000 price tag is no object the casks are hard to come by, outside of the major whisky producers like Suntory & Nikka* who refuse to supply rival whisky makers with casks, Ariake Sangyo is the only cooperage that will supply other distilleries. Mizunara presents a number of challenges:

• High moisture content
• Low cellulose ratio
• Growing time & rarity

*The Nikka Cooperage officially became part of The Nikka Whisky Distilling Co. in April 2010, prior to this it had been run independantly

High moisture content

The name Mizunara is derived from the Japanese mizu for water and nara for oak. The tree has earned this name from its high moisture content. Being so moist extends the drying phase of the wood, because it must only have a residual moisture of approx. 14% before it can be processed into a barrel.

Wastage and stave creation

Mizunara trees typically grow in a twisted almost gnarled fashion in consequence to the severe, windswept conditions of their native habitats, the trees also feature an unusually high concentration of knots. These factors, coupled with the trees lack of waterproofing oil enzymes, means it is neccesary to cut along the grain of the wood and cutting barrel staves extremely difficult. The Japanese oak is also soft and therefore more difficult to bring into shape, this makes it very difficult to build barrels from the Mizunara staves.

Growing time & rarity

The Mizunara Oak is only found in East Asia, its habitat includes Japan, the Korean Peninsula, north-east China and the south of the largest island in Russia, Sakhalin. Coupled with its geographical ratity the trees have a slow growing time. Sourcing raw materials is extremely difficult as the trees take up to 200 years before they reach appreopriate heights, and foresting rights are often suspended to allow them to regrow. The cooperages of Suntory, Nikka, Chichibu and Sangyo must compete at auction with luxury furniture trade to secure raw materials.

Propensity to leak

Mizunara is more porous than other woods and the barrels made from it tend more often to leaks. Jeffrey Karlovitch the master blender of Kaiyo Whisky jokes that in addition to the 3% of whisky lost annually to the angels share whisky makers using Mizunara lose a further “4% to hell”. For this reason cask staves are thicker than conventional ones at around 38mm and must be cut along the grain to minimize leakage. Once sealed Mizunara barrels are suitable for refilling so a large number of re-racked into mizunara for a finishing period.

Popular for finishing

Like American and European oak, Mizunara casks impart their strongest flavours early on. Unlike the former types where this is considered a good thing Mizunara casks are extremely pungent early on. Whiskies matured for only a short time in Mizunara is described as being incense like in flavour. Distillers and blenders are largely of the opinion that whiskies take a long time, typically at least 2 decades, to mellow in Mizunara. The casks are prized several uses later however and so have become extremely popular for finishing whiskies.

While full maturations such as Yamazaki Mizunara and Ichiro’s Malt Mizunara Wood Reserve do exist finishings are perhaps more common, and not only among whiskies. Examples include:

• Glendalough 13 & 17 Year Old Mizunara Oak Finish
• Bowmore Mizunara Cask Finish
• Writers Tears Mizunara
• Cognac Park Mizunara Borderies (Cognac)
• Monkey 47’s Distiller’s Cut 2000 (Gin) Chivas Regal Mizunara, originally released for the Japanese market, is slightly different as only a portion of the blend was matured in Mizunara, rather than it all being finished in the wood.