What is mizunara oak?

Mizunara is the Japanese oak Quercus mongolica var. crispula, a deciduous tree from Japan that in forest management only reaches the size needed for cask wood at around 150 years.

For comparison: American oak is felled after 60 to 80 years. A mizunara trunk large enough for staves therefore stands in the forest about twice as long as the oak from which most whisky casks are made.

The name mizunara literally means water oak, after the high moisture content of the living wood.

Mizunara wood is porous, so staves of this wood easily start to leak on the outside of a cask.

That is precisely why researchers at Heriot-Watt University looked at whether small pieces of mizunara can be fitted as inner staves in a used bourbon cask: the wood then still gives off flavour but does not have to keep the cask watertight.

On top of that comes the slow growth. Because the trees only reach the right size after a century and a half, supply is limited and a cask costs more than one of ordinary oak.

In comparative research, mizunara yielded 2.47 milligrams of trans-whisky lactone per litre after twenty years, against 0.30 milligrams for American oak.

Whisky lactone is the compound that the specialist literature links to coconut-like aromas. The Heriot-Watt University research names sandalwood and coconut as the aromas of mizunara itself.

A tasting note should come from the bottle itself, not from the type of wood. If you would like to know how a particular mizunara bottling tastes, ask at the counter in Bathmen.

Yes. The Scotch Whisky Regulations 2009 require maturation in oak casks of no more than 700 litres, and mizunara is an oak species.

Regulation (EU) 2019/787 sets a comparable requirement for whisky sold in the European Union: maturation in wooden casks of no more than 700 litres, for at least three years, and a minimum of 40 per cent alcohol at bottling.

That is why, besides Japanese whisky, mizunara also appears on Scottish and Irish labels.

A mizunara cask finish means that the whisky spent only the last part of its maturation in a mizunara cask, not the entire maturation.

With full maturation in mizunara, the new spirit goes straight in and stays there until bottling. With a finish, the whisky is transferred after years in another cask, often for a few months to a couple of years.

In both cases the label states only the age of the youngest whisky in the bottle; that is what the 2009 regulations prescribe.

The word mizunara is almost always spelled out on the label, because the wood is scarce and the producer mentions it.

The spelling does vary. Some labels say mizunura or Japanese oak instead of mizunara, while it is the same oak species.

If the label only says Japanese oak without further explanation, ask the producer or the importer which species it is.