All Scotch Whisky must be matured in oak casks in Scotland for at least three years. Nowadays through, especially with Single Malt Whisky, the maturation period is usually much longer.
“Finishing” is a relatively modern extension to the maturation process, in which the whisky is transferred from one cask type to another, for a period of ‘secondary maturation’. This adds complexity to the whisky.
The oak casks used for finishing must have been drained prior to use, so that changes to the maturing whisky filled into them result entirely from interaction with the wood.
All manner of different sized casks are used for both Scotch Whisky initial maturation and for finishing. No cask can be bigger than 700 litres capacity, but there is no minimum size.
The standard sizes used today are listed below. Skene Scotch Whisky will always be transparent about the cask type in which its whiskies have been matured (and finished if appropriate).
Madeira Drum
Madeira fortified wine is produced on the Portuguese Island of Madeira. It is matured in 650 litre “Madeira Drums”, which are manufactured from sessile oak. Typically, Madeira Drums are used to ‘finish’ Scotch Whisky, as they both enhance the colour of the whisky and add interesting Madeira notes to the nose and palate.
Sherry Butt
Sherry is a fortified wine produced from white grapes in the Jerez region of Spain. It is matured (normally in a solera system) in 500 litre “Sherry Butts”, which are produced from American Oak or Spanish Oak. The word Butt derives from the Italian ‘botte’, which means cask. Sherry Butts are used both for Scotch Whisky maturation, and for finishing. Currently, dark sherried whiskies are very in vogue with drinkers, collectors and investors alike.
Port Pipe
Port is a fortified wine produced in certain parts of the Portuguese mainland. It is matured in “Port Pipes”, which hold 500 litres, or sometimes up to 650 litres. They are similar to Sherry Butts, but squatter and more compact. Scotch Whisky matured or finished in Port Pipes can be stunning, but very delicate malts can easily be overwhelmed by the wood.
Demi-Muid
These are double-sized Hogshead shape and contain 500 litres. They are made from either American or French Oak.
Puncheon
A “Puncheon” is dumpier looking than a Sherry Butt and is usually produced from Spanish Oak staves. It typically holds 450 to 500 litres and is normally used in Sherry production. “Machine Puncheons” are constructed from American white oak and used to mature rum. But they have recently become more common in the Scotch Whisky industry.
Cognac Transport
Cognac is a brandy produced in the Cognac region of France. “Cognac Transports” are 300 to 350 litres, made of American or Limousin oak, and similar looking to Sherry Butts. It is relatively unusual for a Scotch Whisky to be wholly matured in a Cognac cask, but there is a growing number of Cognac-finished single malts.
Hogshead
These are casks manufactured from the oak staves of other casks. A Bourbon barrel with added staves becomes a “Bourbon Hogshead” or “American Hogshead”. Hogsheads are also coopered from Sherry casks. Hogsheads hold 250 litres and are crafted from either American or French oak.
Barrique
“Barriques” hold 225 litres. They are the default size in France for wine maturation (eg Bordeaux). Whisky readily takes aromas and flavours from Barriques and they are increasingly popular in Scotland.
Bourbon Barrel
In the States, the law requires that Bourbon must mature in brand new American Oak casks for at least two years. So, once used, “Bourbon Barrels” are useless to American producers. They are therefore sold cheaply to Scottish Whisky distilleries for re-use in whisky maturation. Bourbon Barrels hold about 195 to 200 litres.
Quarter Cask
“Quarter Casks” are small, typically holding 50 to 125 litres. With smaller casks, there is more interaction between liquid and wood. So more flavour is absorbed by the whisky in a shorter period. Quarter Casks are especially popular for finishing Scotch Whisky.
Blood Tub
“Blood Tubs” are tiny, typically holding just 30 to 50 litres. Today they are rarely used for commercial Scotch Whisky maturation or finishing, as they aren’t economical to fill or transport. However, distilleries do sometimes offer Blood Tubs to private individuals who, for whatever reason, want to buy a small cask of whisky.
