All shapes and sizes

All shapes and sizes

Dave Broom looks at how Japanese oak imparts exotic flavours, and the different cask types used in whisky making

Production | 02 Dec 2011 | Issue 100 | By Dave Broom

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The first casks made in Scotland from Japanese oak (mizunara) could be made by the end of this year. Speyside Cooperage, a subsidiary of Francois Freres, revealed that it has been in negotiations to buy the highly-prized seasoned oak from a Japanese supplier. The deal had been expected to have been finalised earlier this year but has been delayed by the situation in Japan after the earthquake and tsunami. All being well the supplies will be in Scotland in autumn.

It is the cooperage’s intention to make the casks at its Speyside base and then sell them to interested parties in the Scotch whisky industry. Scots distillers have been intrigued by the potential of mizunara for a number of years, but have been unable to get access to supplies of the oak. Although only a small consignment will be made available to the Speyside Cooperage it could mark the start of a new chapter in Scotch whisky maturation.

We all know that oak has a significant part to play in the final flavours of a single malt, but it is often hard to ascertain exactly what they may be.
So, we asked Suntory and Venture Whisky if they could give us samples of the same base whisky - same distillery, same style, same age - but aged in different wood types. The results were, we think, fascinating.

The Yamazaki

12 Years Old

(all at 50%)

American Oak

Colour: Light straw.
Nose: Very fresh, fragrant and intense. Estery and floral with a little vanilla/butter. Lemon and baked apple with a little green banana. With water it gets more moss like but also shows a sweet side, think pastries.
Palate: Bigger than you would expect from the nose. Tatami, custard-covered fruits, ripe pears. The floral notes move to lilac.
Fresh acidity.
Finish: White peaches.

Japanese Oak

Colour: Gold.
Nose: Aromatic and robust. Coconut, pineapple, rose, light incense, raspberry and baked fruits. Light oiliness. Fresh acidity. Plenty of sandalwood. Palate: Bitter-sweet with good oakiness. Tight. Red fruits. Medium levels of tannin. Redcurrant and smoked wood. Silky mid
palate, peppery.
Finish: Cherry.

European Oak

Colour: Reddish mahogany.
Nose: Huge, deep and resinous but also sweet and rich. Lots of treacle, dark rum, overripe banana, raisin.
Palate: More grip. Light leathery notes, some cedar. Black fruits: date, cooked plum, but real sweetness balancing the centre.
Finish: Prune.


In all of these the key similarity was the fruity palate weight of the spirit which gave a softness and a ‘thick’ quality to the centre of the tongue. That said, the different oaks all took this basic character and added their own personality. Like a song being remixed you could tell the whisky was the same but somehow different.

The American oak was the most subtle, allowing green fruit to come through as well as a more floral element. These fruits became red and more acidic when put into Japanese oak; there’s a real acidity that seems to come from mizunara as well as a far more intense fragrance. This was more obviously woody and while there wasn’t as much heavy incense as you often get, there was an exotic element. The European oak (ex-sherry) cask turned the fruits black and even dried. What was most fascinating about this was that although there was more tannin on show the real sweetness of the spirit balanced this mouth-drying quality.


3 Years Old

French Oak

Colour: Very pale.
Nose: Slightly yeasty and youthful with a little dustiness. Acetone (nail polish) and yellow plums but it opens up to lots of grassiness and a vegetal character like rhum agricole.
Palate: Clean, sweet spirit. Masses of hot spiciness comes flowing forward along with a delicate touch of mint and cardamom. Water allows a limey citric character and unripe melon to come through.
Finish: Fennel.

Refill Sherry

Colour: Gold
Nose: More rounded than the French Oak. More forward. A distinct sultana note and sweet. Yellow fruit and, with water, buttery and soft.
Palate: Round and soft. Cake mix (butter, sugar, dried fruit). There is also some cut grass but this is more on the herbal side –a return to the fennel and green herbs.
Finish: Zesty still.

Japanese Oak (puncheon)

Colour: Rich gold.
Nose: Masses of spices as well as coconut and some caramelisation. A general, exotic, scented quality. Masses of clove, cassia bark, scented woods with water.
Palate: Spicy with nutmeg, rose petal, sandalwood. More bite and acidity. Grass been replaced with bamboo.
Finish: Clean and sweet.

American Oak (barrel)

Colour: Pale.
Nose: Dried grass, but more sweetness. Needs time and water to allow creamed coconut to come through.
Palate: Zesty again, with lots of gooseberry. Again the grassiness, but the palate has been filled out in weight and sweetness. Thick and chewy.
Finish: Lemongrass.

New American Oak (hogshead)

Colour: Rich amber.
Nose: Instantly more ripe fruits, crème brulée, toffee. Little touches of spice but still the youth is there. Light pine, sweet. Nutmeg.
Palate: Texture is thick and rounded. Small touches of char, caramel and blackberry. Still has the characteristic zestiness. More honeyed.
Finish: Juicy.


Obviously we’re dealing with a young spirit here (albeit one which is extremely well made and clean) As a result the distillery character was a little more apparent than in the Yamazaki while the oak was only beginning to develop. In all of them were variations on a basic theme of sweetness, grassiness and a zesty clean citric element. There is good guts to this whisky though. The French oak was slightly ‘spiky’ as if the oak had yet to wake up something which was obvious when compared with the refill sherry butt where the wood had already covered the alcohol and added elements of its gentle dried fruit character. Once again, Japanese oak added acidity, fragrance and because this was a first fill cask the oak was already more integrated. The refill barrel sat half way between the French, fresh, and the refill sherry, softness. The new oak however was already well on the way to being fully integrated; beginning to dominate the conversation between spirit and cask. A fantastic example not just of the characteristic elements from different oak types: spice from French oak, vanilla, crème brulée from American, dried fruit from sherry and exotic fragrance from Japanese; but of how the number of fills also has a major impact of flavour.

Cask types

The whisky industry around the world uses a number of different types of cask (note “cask” is the correct term, “barrel” is a size of cask) for maturation. These can be both of different sizes (capacity) and also made of different types of oak. Both of these factors will give different flavours to the maturing spirit.

The influence of the size of the cask is determined by the ratio between the wood and the liquid inside the cask. The smaller the cask, the more oak there is for the liquid to interact with. Conversely, the larger the cask, the less oak there is for this conversation to take place. In simple terms, a small cask will deliver a greater impact of wood in a shorter time than a large one. The downside of this is that the smaller the cask is, the quicker the whisky will become overly woody! The number of times a cask is filled will also have a major impact on the final flavour of the spirit. The first time it is used, the cask is at its maximum in terms of flavour and colour compounds. The second time it is filled, so these elements are reduced (because they have been removed by the previous fill). The third time, the flavours are diminished even more, and so on. Eventually, the cask is exhausted and has nothing more to give. It is no more than a neutral vessel for keeping – but not maturing –liquid. Knowing the size of the cask is certainly useful, but knowing the number of fills it has had is even more so.

Type of oak

There are four main ones:

Quercus Alba or American white oak

Gives characteristic aromas of vanilla, coconut, sweet spice. All casks used by the Bourbon industry are made of this type. Some sherry casks are also produced from Q.alba.

Quercus Robur or Spanish/European oak

The most common type of “sherry cask”, this oak is higher in tannin - giving a mouth-drying effect - as well as having aromas of dried fruit, clove and resin.

Quercus Petraea or Sessile oak or French oak

Used primarily by the Cognac industry but some is now being used in the Scotch and Japanese whisky industries. In flavour terms it sits in between Q.alba and Q.robur with high tannins and also a lot of spiciness.

Quercus Mongolica or Japanese oak/mizunara

Rare and expensive this species is now growing in popularity as it gives an intensely fragrant aroma of incense , sandalwood as well as pineapple and coconut.

Size of cask

Most commonly used:

Bourbon barrels [aka ASBs/Yankees]

These are made of Q.alba and contain 200l of liquid. By law the Bourbon industry may only use new, heavily-charred oak barrels. Once used in America they are sold to Scotch, Japanese, Irish and Canadian whisky distillers as well as rum and tequila producers.


This type of cask contains 225l and is most commonly made from Q.alba. They are made by breaking down a Bourbon barrel, adding some more staves (thereby increasing its capacity) and new heads (ends). Most of the whisky matured in Scotland and Ireland is aged in this size of cask.


500l in size, these are otherwise known as sherry casks. They are most commonly made from Q.robur and have been seasoned with sherry prior to being shipped to whisky distillers. Some will be made from Q.alba. These days, all new sherry butts are made to order for the whisky industry.


These are the same size as butts but are shorter and fatter in shape. They can be made from either Q.robur or Q.alba.

Other types of cask:

Madeira drum / port pipe

Larger in size than butts at 650l these are mostly used for secondary maturation (aka finishing) though some distillers are now experimenting with long-term maturation. Madeira drums are traditionally made from Q.petraea while Port pipes are mostly from Q.robur.


Otherwise known as a wine cask, these will vary in size between 225l and 300l and can be made from either Q,alba or Q.petraea.


The largest legal size of maturing cask, at 700l, Gordas (the name means ‘fat one’) were shipping casks used for transporting sherry to Scotland and Ireland and were made from Q.robur. They are rarely seen or used these days.

Quarter casks / blood tubs

The smallest size of casks at 50l and 40l respectively, these are specially coopered mostly from Q.alba.

Quarter casks are used commercially by Beam International for short-term finishing purposes at Laphroaig and Ardmore. These are sometimes called “firkins”.

In the past, quarters and blood tubs would have been used for private customers of distilleries. Blood Tubs are still used in this fashion by Bruichladdich for people who wish to lay down their own whisky.
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