Cask are made (mostly) out of oak staves, usually kept
together with metal bands. Making and repairing those
casks is a craft, performed by coopers at cooperages.
Furthermore, wood is a natural product. For one thing,
this means that the properties vary from cask to cask.
The word ‘cask’ describes any wooden container that
is used to contain, mature or transport wine, whisky, etc.
When it comes to Scotch whisky casks there are
basically two varieties; ex-bourbon casks imported
from the USA and ex-sherry casks from Europe.
Other types of casks have been used occasionally.
In the distant past, wooden casks were used for storage and shipping.
Casks are not widely used any more for storage of products (grains, fish, meat, etc.),
but some beverages and spirits are exceptions. Maturation in wood is crucial there.
As far as shipping is concerned: whisky is shipped mostly in tanker trucks these days.
Or whisky bottles of course - but that’s an entirely different topic...
When it comes to whisky maturation in casks, there are six important issues;
the wood that is used, the history of the cask, the shape and size of the cask, the
storage conditions during maturation, usage for finishing and the refilling of casks.
Yeah, that’s right - always keep in mind that most whiskies are matured in refilled casks, not fresh ones...
The casks that are used for the maturation of wine and whisky
are made almost exclusively from oak - mostly White American
Oak (Quercus alba) and European Oak (Quercus robur).
The Sessile Oak (Quercus petraea) is very rarely used.
The phrases ‘American Oak’ and ‘European Oak’ are used
on whisky labels and in advertising a well, but this can be a little
confusing. Many people favour whisky from sherry casks over
whiskies matured in bourbon casks - and sherry is only made
in Europe, while bourbon is made exclusively in the USA.
So, ‘European Oak’ means sherry casks, right?
According to whisky expert Dave Broom and other sources, the
sherry producers in Spain have actually been using mostly
American White Oak solera casks since the late 19th century.
Sherry makers don’t rely on the wood for flavour, so they prefer
‘inactive’ casks that don’t have too much effect on the sherry.
Further confusion can me caused by the fact that not all ‘American white oak’ is actually Quercus alba from a
biological perspective - and lumberjacks and coopers both have their own secret language for the guild members.
Whisky writer Davin de Kergommeaux also points out: “Various oak species and subspecies are used in American
cooperages depending on season, weather and availability. American cooperages use a lot of wild oak so there
are few pure stands whereas European cooperages use farmed oak so the stands are closer to pure (by species.)
White oak is a lumber-trade term in the U.S. and includes non-Quercus species, including at least one chestnut.”
When Zac Palmer Laporte
read some overly simple
statements that I made in
the Beginner’s Guide he
offered some insights:
Whisky matured in certain kinds of used wine casks can take on characteristics of the (fortified) wines these barrels contained. In order to understand the role of these barrels in whisky maturation it helps to be familiar with the styles of wine they held. By far the most common wine barrel used to mature whisky is the sherry butt with a capacity of around 500 litres. There are three styles of sherry that are relevant to whisky production:
Fino sherries are pale dry wines that have aged in barrel under a blanket of film-forming yeast. They tend to have a very distinctive doughy, bakery-like smell and show characteristics of tart fruits (green apple) if they show any fruit at all. These barrels are unusual for whisky maturation because the wines take on more flavours from the yeast than the barrel, and the influence on the spirit would be subtle.
Oloroso sherry is most often used for whisky production. It’s a dry wine, aged “oxidatively” - in contact with oxygen. Over time this process causes the wine to darken and take on characteristics of nuts (hazelnut, peanut, almond, walnut... you know - nuts), burnt caramel and sometimes aromas of leather and tobacco and furniture polish. If Oloroso shows any fruit characteristics, these might include candied orange peel, and dry figs. All of these characteristics can marry quite well in a malt whisky and add desirable complexity to the finished spirit.
3. Pedro Ximénez
Unlike the two other styles of sherry Pedro Ximénez is sweet. Really sweet. Whereas most wine is considered sweet with residual sugar above 45g/l. the legal minimum for PX sherry is 212g/l. and most wines are far in excess of this threshold. The wines are made from sundried Pedro Ximénez grapes and oxidatively aged. Used PX barrels can be used in whisky maturation to impart colour, sweetness, and some prune fruit characteristics. Drinkers should be advised - however - that sweetness and colour are also results obtained from a tactical addition of caramel. It is not always clear whether these features in a malt whisky are due to one or to the other.
A cask is made from oak, but it can only be used to
mature Scotch whisky once it has been brought
to life by (fortified) wine or bourbon. So, in a way
this ‘past life’ of a cask may be the crucial part.
The vast majority of the casks used to mature Scotch
whisky are ex-bourbon casks. That does makes sense;
in recent years the oak casks that were actually used
to mature sherry have become increasingly rare.
There simply are less sherry drinkers than before.
The Scotch whisky industry is nothing if not creative.
For one thing, they use sherry shipping casks for
the maturation of their whisky - not the solera casks.
And when housewives around the world collectively
started to drink less sherry in the 1980s and 1990s
they made a deal with the sherry industry.
Sherry producers would equip Scotch whisky distillers
with especially seasoned casks that (had) actually
contained sherry (or must) - but not for very long.
It was therefore not necessarily very good sherry...
Most Scotch whisky that is distilled is aged in bourbon
casks these days, but thanks to the art of blending the
effects of sherry casks are felt in many of the bottled
whisky that is sold world-wide.
It is worth adding that the popularity of sherry-finished whiskies has nurtured a cottage industry in Jerez that produces Oloroso-style wines to season barrels. After a time (usually three years) the barrels are drained and the wine is distilled into brandy. We can be polite and say this is because this wine does not meet the stringent quality standards for sherry. The barrels are then sold off at a premium to a Scottish distillery. Unfortunately when inferior wines seep into a cask they rarely produce superior malt.
But why does the Scotch whisky industry likes to use
so many of those ex-bourbon casks? Well, that would
partly be because of the specific characteristics that
those bourbon casks pass on to the Scotch whisky.
But another reason could very well be the fact that
bourbon casks are much cheaper than sherry casks.
The American laws for bourbon production dictate that
the distillers can use their casks only once. (This nifty
little rule was worked into the laws by lumber unions.)
This means that those casks are useless after a single
use - and the Scots can get them on the cheap...
WINE IN WHISKY MATURATION
One problem with these seasoned casks is that they
are almost always heavily sulphured in order to kill
any germs. The sulphur that is used in the process
can carry over into the whisky - and that’s not nice.
(Some people are extra sensitive to sulphury notes.)
While the majority of the casks that are used for
Scotch whisky are ex-bourbon and ex-sherry casks,
some other cask types are sometimes used as well.
For finishing many different ex-wine casks have
been used; burgundy, chardonnay, chenin blanc,
claret, madeira, port, sassicaia, sauternes, etc.
The ‘history’ of a cask before it was filled with spirit
is important - but from a whisky drinker’s perspective
the time the whisky matures inside the cask is part
of that whisky’s history as well. If the cask was stored
inside a traditional dunnage warehouse, the fickle
Scottish weather may have played a role as well.
Last but not least: refilling or re-racking casks is
a fairly common practice in Scotland. The producer
is only legally required to identify the last cask that
has been used. It’s advisable to carefully read the
fine print on the label of a bottle of whisky.
At some point I got lost in the old measurements, international differences and various industries (wine, sherry,
whisky, port, rum, beer, etc.) that felt the need to invent their own names for specific sizes and shapes of casks.
What’s more important, casks are made by artisans from different species of oak (a natural product), so there are
bound to be differences between individual casks. Every cask is unique and should be approached as such...
Whisky and wine contain alcohol - which is a taxable substance.
Each government levied taxes and in the past each country had
its own system of weights and measurements. To make matters
worse, they sometimes used the same name for quantities or
distances that varied between countries - like the pound or mile.
Researching the sizes and shapes of whisky / whiskey casks
was fun - at least for a while. In past centuries casks were very
important for the trade and transport of so many goods, so now
that we have the internet a person like me can get distracted by
all the free knowledge that is available these days.
The contents below are averages - and the range of sizes varies.
During the 1990s Glenmorangie pioneered the marketing of
finished whisky from non-traditional casks like port or madeira.
However, the practice of re-casking and re-racking whisky into
other casks to fine-tune its character was not new at the time.
The Scots just used mostly bourbon and sherry casks before.
The success of Glenmorangie inspired thousands of experiments
in later years with all sorts of exotic finishes. Personally, I’ve tried
whiskies that were finished in casks that had previously contained
rum, cognac, port, barolo, bordeaux, madeira, marsala, moscatel,
rioja and sauternes wine - and that list is by no means complete.
The ‘finishing’ fad may seem past its zenith these days.
Or rather, that would seem to be the case because we see less
labels proudly proclaiming this or that finish than in the early
noughties. However, keep in mind that the rules of the SWA
concerning the treatment of whisky and casks allow all sorts
of creative jiggery-pokery - for example:
Single cask bottlings are as exclusive as you can get, right?
Yeah, pretty much. Whenever a PR agency re-invents the tired
old gimmick of releasing just one or a few bottles of a particular
whisky, nobody seems to wonder what happened to the REST
of the whisky from that cask. I don’t think they threw it away...
All the specifics we can see on many whisky labels these days
do suggest a lot of transparency. However, all those details are
distracting unsuspecting customers from the fact that they only
pertain to the LAST cask that the whisky spent time in. A lot of
whisky spends its life in different casks before being bottled.
The bottler can decide for himself if he declares it a ‘finish’ or not.
Another important issue is the storage of the casks while the
whisky inside it ages. This happens in special warehouses in
Scotland. In the past (almost) every malt whisky distillery had
its own warehouses on site, but these days part or even all
of the casks may be stored in a separate facility off site.
This doesn’t seem to fit with the ‘whisky region’ theories.
There are two types of Scotch whisky warehouses.
The traditional dunnage warehouse is a low, stone-walled
building with earthen floors. A modern racked warehouse
is higher and often made out of concrete, cement and steel.
Casks can’t be stacked higher than 3 rows in dunnage warehouses.
The wood of the bottom row simply could not support the weight of the upper rows if they stacked them any higher.
Racked warehouses have special steel racks (hence the name) which can easily support 10-12 rows of casks.
But the topic of whisky storage deserves a special page, which will be added to Malt Madness in due time...
950 Litres - Tun (UK)
900 Litres - Tonneau (Bordeaux)
700 Litres - Gorda
650 Litres - Drum
550 Litres - Butt
550 Litres - Demi Muy
475 Litres - Pipe
320 Litres - Puncheon
240 Litres - Hogshead (USA)
225 Litres - Barrique (France)
200 Litres - Barrel (USA)
160 Litres - Tierce
120 Litres - Barrel (UK)
110 Litres - Feuillette (France)
080 Litres - Kilderkin (UK)
070 Litres - Rundlet
055 Litres - Quarteau (France)
050 Litres - Quarter Cask
040 Litres - Bloodtub
040 Litres - Firkin
020 Litres - Pin
Quarter Cask (USA)
A barrel in the UK is 1/8 tun, containing +/- 120 litres.
Bourbon barrels from the USA hold about 200 litres.
A French 225 litre cask, producing +/- 300 bottles.
About 40 litres with an oval shape for horse backs.
A butt (half a tun in the UK) holds +/- 500-600 litres.
French Demi Muy casks contain 500-600 litres.
At +/- 650 litres (Madeira) drums are large casks.
The feuillette is a small French cask, +/- 110 litres.
One firkin is a quarter barrel or 9 imperial gallons.
A Gorda is close to the max. allowed Scotch size.
Half a butt in the UK (+/- 300 L.), but often smaller.
A Kilderkin is half a Tierce or British Brewery Barrel.
A small 20 litre cask in the UK - half a firkin.
A port pipe is similar to the UK butt, about 500 litres.
The puncheon (or tertian) holds a third of a tun.
A quarteau (quarter barrique) holds +/- 55 litres.
The American Quarter Cask is a feeble 50 litres.
This small UK cask (1/14th tun) holds +/- 70 litres.
A tierce is a sixth of a tun, circa 150-175 litres.
Large Bordeaux casks, holding +/- 1200 wine bottles.
A tun (in the UK) is the largest cask; 240-256 gallons.
This was just a tiny selection of the cask sizes that are available. This page doesn’t provide enough space to give
the topic of cask shapes the attention it deserves, but I may add a separate page on that topic later. Also, when
French Master of Wine Olivier Humbrecht provided some information on French casks he stressed: “Traditionally,
each region has used it's own words for things like casks, which may explain why you can find different contents
listed in various sources for the same cask name. So, it is important to specify where a certain cask was used.”