Understanding your cask


Angel’s Share

Every year, a small amount of alcohol evaporates from maturing casks. The rate of evaporation through the oak is affected chiefly by temperature and humidity. The resulting airborne alcohol encourages the growth of the ‘Angel’s Share Fungus’, which grows freely on most nearby exterior surfaces. 



ABV stands for Alcohol by volume, and is usually measured as a percentage. Whisky is required to have an ABV of at least 40, and cask strength whiskies may reach well into the 60’s.



Previously used in the production of Bourbon, they give whisky its signature golden colour and coconut and vanilla flavours. Barrels contain 200 bulk litres, around 120-130 Original Litres of Alcohol (OLA).


Blended Whisky

Whisky produced by blending a number of single malts with a base of fairly neutral grain whisky. Blends were the primary form of whisky drunk for many years, and can vary from relatively cheap Scotches to some of the finest in the world. The art of blending is one of the most respected in the industry. The blender, through careful mixing, can create almost any style of whisky he pleases with the ingredients at hand.



Oak barrels, or casks, are used for the maturation of whisky from all over the world. The wood softens the spirit, adds colour and flavour and helps to remove impurities. The ‘barrel’ is in fact a particular type of cask imported from the USA. The Sherry ‘butt’ is much bigger, and wine casks are often known as ‘barriques’.


Cask Finish

A secondary maturation in a different cask type. Bourbon cask matured whiskies are often re-racked (where the whisky is moved from one cask to another) into sherry butts or port pipes. The previous liquid held into the cask becomes ingrained into the wood, imparting its character onto the casks next filling. For example, whisky aged in a cabernet sauvignon casks will take on a reddish hue, a tannic mouthfeel and a fruity, cherry-like flavour.


Cask Strength

The majority of whisky is diluted to 40, 43 or 46% before bottling. This is to make the whisky softer on the palate and to increase quantity. However, many enjoy their whisky to be at ‘cask strength’, or the ABV that the whisky is when it leaves the cask. This is often significantly higher than normal bottling strengths, and a drop of water is often necessary to release the flavours in the whisky. Cask strength whisky is normally associated with limited releases where it is desirable to maintain the original character of the cask.



Whisky casks are commonly charred on the inside. Similarly to how the beneficial effects of oak ageing were discovered by accident, charring was most likely the unexpected result of a rather fiery mishap. The toasting of the oak re-actives many of its organic enzymes, caramelising the sugars and reinvigorating the vanillins and tannins. The resulting layer of carbon acts as a charred filtration barrier removing sulphur compounds from the whisky, and the resulting cracks and grooves encourage the spirit to penetrate even deeper into the wood.



Chill filtration

This is a technique commonly used to remove the fatty acid esters from whisky. This is purely cosmetic, as whisky that is below 46% can appear cloudy and develop sediments if cold. The practise was developed the Scots when they started exported their whisky to the USA, where it was common to add ice to their scotch. The whisky is chilled to between -10 and 4 degrees Celsius before passing through a fine absorption filter. Many claim that this can have a negative impact on the depth of flavour. Together with the high cost of chill filtration, many smaller distilleries now bottle their whisky at 46%.


Column Still

Also known as the continuous still, the column still is an Irish invention that allows a gradual flow of wash into the still, negating the need for batch distillation. The most commonly used design is by Aeneas Coffey, and is used for the distillation of grain whisky due to the high volume of high ABV spirit it can produce. 



The process in which the spirit vapour is cooled and condensed back into a liquid following distillation. The condensation process can often affect the flavour of the whisky, especially if an old-fashioned copper worm tub is used.



The cooper is in charge of assembling and maintaining the all-important casks. It takes many years to become a master cooper, as hand tools are still in regular use. Thousands of casks a year require major repairs, and thousands more require re-charring.



Distillation is the process in which alcohol is extracted from fermented products through selective boiling and condensation. It is a physical separation process rather than a chemical reaction. Distillation is used to create new-make spirit for whisky from the wash, and is an essential part of whisky production.



Grain residue left behind when the liquid wort is drained away following mashing. It is very often used as animal feed due to its high protein content.


Drum Malting

Also known as a Rotary Drum, this is a modern technique for malting barley, in which a large drum containing wet grain is slowly revolved to prevent the rootlets becoming matted. The largest malting drums in Scotland are located at Port Ellen Maltings on Islay.



An expression is simply another, more romantic word for bottling.


Floor Malting

The traditional method of malting barley, in which the grain is spread out over a large floor. Although highly labour intensive and often inconsistent, this method allows for a better retention of peat-smoke flavours due to the higher levels of surface moisture.



Once the malted barley is dried, it is ground down into grist before the mashing process to increase the solubility of various sugars.






Geographical the largest whisky region in Scotland, and correspondingly the most sparsely populated by distilleries, the Highland malts vary enormously in style. Famous distilleries include Brora, Glen Garioch and Dalwhinnie.



Most often used in bourbon production, a Hogshead is a barrel with the addition of extra staves to a barrel creates a 250 bulk litre cask, typically around 150-180 OLA.



The Island malts are found off the west and north coasts of Scotland, but do not include whiskies made on the Isle of Islay which is a region in its own right. Malts include Highland Park, Talisker and Tobermory.



Many of the worlds most distinctive malts are produced on Islay, and are often noted for their fiery peat-smoke flavours. Located off the west coast of Scotland adjacent or the Isle of Jura, the remoteness of Islay necessitated the use of local peat in the malting process. Notable distilleries include Laphroig, Port Ellen and Lagavulin.



Malted barley is dried in the kiln to curtail germination, prevent it spoiling and so that it can be easily ground into grist. Hot air from the kiln passes through the barley and out of the distinctive pagoda roofs of the Kiln house. This is the stage at which peat can be added to the kiln, and the peat-smoke will pass through the barley imparted phenols into the kernel of the barley.



The most southerly whisky making region, the Lowland distilleries can be found south of Edinburgh and Glasgow. Glenkinchie, Auchentoshen and Bladnoch are the most well known, with legends such as Rosebank, Ladyburn and St. Magdelene long gone yet commanding ever increasing prices. Lowland malts are often light and floral in style.



Germinated cereal grains that have been germinated and dried to produce the necessary enzymes and sugars for fermentation. Malt is also an abbreviation of single malt.



The process in which grain is soaked in water to encourage germination, then dried with hot air to produce malt for the production of whisky. The malting process was traditionally performed on site, but today many distilleries buy in ready-malted barley.



Mashing is the process in which fermentable sugars are extracted from the grain. The grist is soaked in hot water (between 62-70 degrees) for a period of time, which encourages starch to be broken down into sugars through the activation of an enzyme called amylase. The resulting brown sugary liquid known as ‘wort’ is then extracted, with even hotter water (95 degrees) being used to extract any remaining sugars from the grain - this part of the mashing process is known as ‘sparging’.


Mash Tun

This is a large cylindrical vessel in which the mashing process takes place. The mash tun keeps the mash at a steady temperature, and often an automated ‘mash rake’ is employed to stir the contents ensuring consistent temperatures.


Master blender

A master blender is responsible for creating and blending whiskies using different combinations of distilleries, cask types and vintages. He is primarily responsible for maintaining consistency. Richard Patterson, master blender for Whyte and Mackay and Dalmore, has a £2.6 million insurance policy just for his nose.



The production process gives the whisky roughly 20-30% of its style and flavour, with the rest all being extracted from the maturation process. Oak is an extremely durable wood but is also slightly porous, allowing the cask to breath. In humid conditions such as those found in Scotland, this allows a small amount of alcohol every year to evaporate into the air (the Angel’s Share), but also draws the spirit deep into the wood. As temperatures fluctuate from month to month and year to year, the wood slowly expands and contracts. The spirit is drawn in and out of the oak, softening it and imparting flavour and colour.


The type of oak and the liquid that was held in the cask is also of the greatest importance to maturation, as the wood will still hold a lot of the flavour imparted by its previous occupant. Bourbon barrels and Sherry butts are the most common. American oak bourbon casks impart a sweet, vanilla, honeyed notes, whereas European oak sherry casks give the whisky a spicy, nutty and dried-fruit characteristic.



Also known as the ‘Swan’s neck’ due to its distinctive shape, the neck is found at the very top of the still. It collects the rising vapours and sends them down the ‘lyne arm’. The shape and curvature of the swan’s neck has a fundamental impact on the character of the spirit, as it affects both reflux and condensation.



Original Litres of Alcohol - the original litres of alcohol first put into the cask.


Also known as ‘turf’ in Ireland, peat is an organic deposit that is best described as being halfway between earth and coal. When dried, it burns very slowly, releasing a distinctive smoky aroma. Often used in the malting process, the smoke imparts phenols into the barley that result in a whisky being ‘peaty’.


Pot still

The type of still used for batch distilling, and the only type allowed in the production of single malt whisky. Pot stills are essentially large copper kettles with long necks that are used to extract alcohol from the mash via evaporation. Pot stills are made in a range of shapes and sizes depending on the quantity and style of spirit desired.



Reflux occurs in taller stills where some of the heavier compounds in the vapour condense before they can pass over the swan’s neck. This leads to them being re-distilled, and often results in a lighter, more delicate style of whisky.



Regauged Litres of Alcohol - the remaining litres of alcohol in the cask after re-measuring at a known date after the original filling


Shell and tube condenser

The most commonly used and efficient condenser type, shell and tube condensers utilise an extensive series of water-cooled copper pipes within a shell. The quicker cooling process and larger amount of copper contact results in a lighter, more delicate style of spirit than the traditional worm-tub.


Sherry Butt

Previous use in sherry production makes these casks extremely desirable as they impart a distinctive colour and strong rich flavour. Sherry butts are amongst the largest used in Scotch production at around 500 bulk litres or 300-330 OLA.


Single Malt

Whisky that is the product of just one distillery, rather than a ‘blend’ consisting of whisky from multiple distilleries.  



By far the largest scotch malt whisky region in Scotland, Speyside takes its name from the river Spey by which so many of the distilleries are situated. Over half of all Scotland’s distilleries can be found here, included many of the biggest names such as Glenfiddich, Macallan and Glenlivet. The region rose to prominence during the late 19th century due to the plentiful supply of fresh water and barley.


Top Dressing

Only the best whiskies used as ingredients for blends are referred too as a top dressing. They give blended whiskies their smoothness and complexity.


Vatted Malt

A blend of single malts from different distilleries, a vatted malt contains no grain whisky. Vatted malts are not very common, but are often superior to blended scotch. 



Maturing casks are kept in secure bonded warehouses. The traditional ‘dunnage’ warehouses found on site at many distilleries have thick stone walls and earth floors that help to maintain consistent temperatures and humidity.




Essentially huge fermentation tanks, washbacks are large cylindrical vessels used for the fermentation of wort. They are traditionally made from Oregon pine, although many modern washbacks are made from steel. Some distilleries such as Caol Ila  have not upgraded from their original washbacks, claiming that it will affect the flavour of the whisky.



A traditional form of condenser, the worm-tub consists of a coil of copper piping immersed in a large tub of water. Vapour passing through the copper coil is slowly cooled, condensing into neat spirit.



The brown sugary liquid that is produced during the mashing process, the wort is fermented using yeast, turning the sugars into alcohol.