A glossary for a cask owner

February 27, 2023
The following glossary will teach you the key terms you need to know in order to talk about whisky casks, whether you’re a cask owner, or an aspiring cask owner.

When you are initiated into the world of whisky, there’s a whole lexicon that goes with it. We whisky fans have our own jargon that comes with the territory, enabling us to talk coherently about our whisky, and maybe show off a little into the bargain. Words like ‘malt’, ‘new make’, ‘phenols’ and ‘sherry bomb’ enter into common usage.

Once whisky love is established, the next step may well be investing in a whole cask of it. Whisky cask ownership is growing in popularity – a new way to show one’s undying love for the amber spirit, and leave your own distinct impression upon it (and it on you). Once you take that step, you’ll find a whole new world of technical language awaits.

Fear not! Whether you’re investing in a cask to design your dream whisky, to create a gift that matures along with you and your family, to make a unique whisky to kick start your independent bottling business, or invest your money in something you love; this handy guide will introduce you to the most important terms you need to blag your way into the esteemed and select company of whisky cask owners.

Angels’ Share

Evaporation of alcohol from the cask while it is maturing in the warehouse. This is a natural occurrence and is commonly thought to be about 2% of the total liquid every year, though this is just a rough average and can be affected by the age of the whisky, the size of the cask and the location of the warehouse. A small cask stored at a warmer temperature is much more vulnerable to angel attack. Angels’ share tends to slow down as the cask gets older.

ABV – Alcohol by Volume

A vital measure for a whisky that is ready to be drunk – this provides a number for what proportion of an alcoholic drink the alcohol takes up. Water can be added to whisky when it is bottled, lowering the % abv. For whisky, the legal minimum is 40% abv, though cask strength whiskies are stronger – sometimes into the low 60s.

We like a cask strength whisky here. It gives the drinker the chance to tailor the strength of their whisky for themselves – and experience some pretty punchy flavours.

AYS – Age of Youngest Spirit

The AYS is a common abbreviation for ‘age of youngest spirit’. Since there is a strong tradition of blending whiskies together in Scotland, the legal requirement to declare the age of the youngest spirit in the bottle prevents unscrupulous blenders from mixing 90% 5 year old whisky with 10% 30 year old and labelling their whisky as a ’30 year old Blended Scotch’. Interestingly, this means that many Scottish blends and blended malts that carry an age statement may well contain whisky that is far older than the age declared on the label. Not a bad deal for the customer!

You will see the ‘AYS’ used to record the age even on indisputably single origin, unblended casks of whisky – it’s an industry standard and it keeps us honest!

Bonded Warehouse

Whisky is a duty-suspended substance, meaning that tax only has to be paid on the alcohol when maturation is over and the whisky is being bottled or exported. This means that casks of maturing whisky must be strictly observed to ensure that nothing disappears before proper taxes have been paid on it (angels, following the laws of heaven and not earth, are naturally exempt).

A bonded warehouse is a consecrated piece of ground in the whisky world – a place that is staffed and fully certified by HMRC to look after maturing whisky and maintain that highest degree of trust. It is illegal to hold a maturing cask of whisky anywhere else, until the duty has been paid on it. The upside of this is that every cask of whisky has one of the highest governmental bodies vouching for its location and authenticity at all times.

Bulk Litres of Alcohol

Even the strongest grain spirit is not fully 100% pure alcohol – it’s a mixture of alcohol, water, aromatic compounds and other substances that give a whisky its character. The proportions of all these compounds can change a lot over the course of a cask maturation, making accurate measurement difficult.

For simplicity of record keeping, it’s just the alcohol in the cask that is measured when samples are taken. For example, if a cask is filled with 250 litres of new spirit at 63% abv, then it contains 0.63 x 250 = 157.5 bulk litres of alcohol.


A delightful word, and ripe territory for juvenile puns, a bung may be the most important part of a whisky cask. Essentially a wooden cork that seals the cask once it has been filled, the bung needs to be snug enough to prevent whisky leaking when the barrel is rolled around the warehouse. Specialist tools are needed to remove a bung if a whisky is being sampled or re-racked, and the old bung is often not reusable.

Bungs are made of poplar, and they do make physical contact with the whisky in the cask, meaning that whisky is, technically, not 100% oak matured – there’s about 0.2% poplar in there too.


Oak wood by itself is not quite enough to have a desirable effect on the maturation of whisky – the inside of the cask needs to be prepared by charring it over a fire until it’s nicely toasted, if not completely blackened.

Char can be light, medium, heavy or alligator (as the heaviest firing cracks the wood up like alligator scales).

This charring breaks down lignins and other structural molecules in the wood, converting them to caramel sugars that flavour and colour the whisky as it matures. Furthermore, charcoal attracts and absorbs sulphur, so a nicely charred cask prevents a whisky from tasting too much like a fart that’s been trapped for 20 years.

Cask Sample

A vital part of a whisky’s maturation. 50-200ml samples should be taken from the cask from time to time (every 3-5 years) in order to check up on its development, identify issues and enjoy the progression of flavours.

You can order a cask sample from us for £50 and we will ship it to you anywhere in the world. If you’re in Scotland and want to truly get in touch with your developing cask, organise a cask visit with us at our Viewfield warehouse in Craigellachie, Speyside.

Dunnage Warehouse

All traditional Scottish Warehouses are dunnage style. Long, low buildings without windows. The floors are earthen, sometimes with wood ash mixed in to maintain greater humidity (this regulates the environment in a way that casks rather enjoy). Older dunnage warehouses will be made of stone, though more recently built ones may have steel walls – like the one where the great majority of Cask 88 managed casks live.

The key to a dunnage warehouse is how casks are stored. They can only be stacked on wooden racks (stows) to a maximum height of three casks on their sides. This lowrise construction ensures good airflow even at the centre of the stack, and gives all the casks an equivalent  and stable environment to mature in.

The disadvantage to dunnage is how labour intensive it is. The warehouses are not large enough to admit heavy machinery like forklifts, so warehousemen have to manoeuvre casks by hand, rolling them along. If a cask is located at the bottom of a long row – bad luck: the only way to get at it is to remove all the casks that are in front and on top of it first.

Though less efficient, it’s this hands-on approach to cask management that is so alluring about dunnage warehousing. Every cask really does require individual attention here. So, for the love of goodness, if your cask is stored in dunnage, please do give the warehouse workers a good period of notice before getting a sample or a regauge – they have their own complex and ineffable ways of managing the movement of casks.

Duty Suspension

Almost as long as they have existed, alcoholic products have been taxed by whatever authority claims ownership of the land – in our case that is HMRC. The alcohol in a maturing cask of whisky is a tricky proposition to tax, because there is never a stable amount of it – alcohol % in the cask changes over time. To keep the taxation simple, duty is paid on whisky at the time it is bottled, and the amount of duty paid is based on how much alcohol there is in the cask at this time. For the years until bottling, a cask of whisky exists in a kind of tax limbo, classed as a ‘duty suspended’ product.

The upshot is this: since %abv in a maturing whisky almost never increases over time (you’re in a weird corner of the globe if your whisky is getting stronger), less duty is usually payable upon bottling older whiskies than younger ones. As if there weren’t enough reasons already to mature a whisky properly!

Dry Goods

Everything to do with the complete bottle of whisky that is not the whisky itself. The dry goods are empty bottles, printed labels, bottle stoppers or corks, foil caps, presentation boxes or tubes, or any of the other accoutrements that contribute to the beauty of a special whisky bottling. The creation of these dry goods is the domain of our design team, and they must be united with the whisky at the bottling hall when it comes time to fill the bottles and assemble the final product.


When you ‘first-fill’ a cask, that’s referring to the whisky. Regardless of whether the cask formerly held Kentucky bourbon, Spanish sherry, French wine, or nothing at all, when you first fill it with Scotch spirit, that is its first fill. First-fill casks are often seen as the most premium – being fresher, they will be able to impart the strongest flavours into the whisky they sped time maturing. Intense ‘sherry-bomb’ whiskies can be obtained from first-fill casks seasoned with sherry, while first-fill ex-bourbon hogsheads yield strong vanilla, coconut and toffee flavours. The more times a cask is used, the midler these donated flavours become – so first-fill is all about intensity.


Her Majesty’s Revenue and Customs: a non-ministerial government body which oversees the collection of taxes in the UK. A very big deal in the whisky industry, as it is HMRC regulations that determine where and how whisky can be matured, and what amount of tax is payable on the alcohol at the time of bottling or export. The careful scrutiny of HMRC helps guarantee the veracity of every whisky cask – nothing slips through the cracks!


Intermediate bulk container. A storage vessel for whisky when it is not in a cask. These will keep the whisky stable as it is being transported and as a result have nothing to do with the maturation process. Definitely not as pretty as an oak cask, but a vital link in the chain.


It is a legal requirement that all casks that are to contain Scotch Whisky must be made of oak wood. The oak can come from any country and primarily comes from the United States, with Spain, France and Eastern Europe providing a good amount as well.


Original Litres of Alcohol. This is the amount of pure alcohol stored in the cask as measured at the time it was first filled. The OLA is calculated from the total volume filled into the cask and the alcoholic strength of the spirit (casks are most commonly filled with spirit at 63% abv.). The precise OLA is important to know, as this figure will be the reference for all future measures of RLA.

Palletised warehouse

A modern style warehouse where casks are stored on their ends, stacked on wooden pallets which in turn are stacked on top of each other. It’s admittedly an impressive sight, as these pallets of casks can be many metres high, and like a drystone wall, only careful construction and the force of gravity holds them together.

Palletised warehouses are designed to work with forklifts, which makes the job of the warehouseman a bit easier, in terms of raising and lowering casks into place. The stacks are so dense, there is less air circulation around the individual casks. It’s not feasible to work with casks in small numbers in such a warehouse – the density of storage and sheer numbers of stacked casks require that cask movements are done in bulk here. Perfect for the larger distilleries in the modern whisky business.

Racked Warehouse

A racked warehouse consists of a strong metal scaffold, with individual chambers that can each hold a row of casks. These structures can be many metres high, and many rows deep. None of the casks are physically touching, so it is feasible to move casks in and out quite efficiently, with the right heavy moving equipment. Airflow around the casks is quite free, though the microclimate at the centre of a large stack may still be different from the outer edges. The racked warehouse represents a fair balance between dunnage and racked styles. There are stairs and gantries between the rows of casks, meaning that individual attention can be given to individual casks in a rack, while the metal framework allows for large numbers of casks to be stored safely and vertically.


A refill cask will already have stored whisky at least once before in its life. This is not counting any previous bourbon whiskeys (which can only be filled into a cask once). Almost all casks in Scotland will have started life as bourbon casks, but will still technically be ‘first-fill’ when it comes to their first exposure to Scotch whisky.

We do not waste good resources, and whisky casks can remain viable for many decades. If a cask stores a whisky for 10 years, it can easily be refilled with another whisky for another round. Some casks see up to 6 or 7 fills in their lifetime, shaved and retoasted between each filling.

Refill casks do not give flavours to the whisky as strongly as first-fill casks, but the reductive and transformative effects of matuation are still at work, making more subtle changes to the flavours while maintaining the original character of the whisky. A popular strategy is to begin maturing whisky in a refill cask, and then re-racking it into a first-fill cask for finishing with extra flavours.


To regauge a cask means to perform a check up on its contents. The cask is weighed, emptied into an inert container and weighed again, and the strength of the alcohol within is measured. This will tell the warehouse workers the current status of the maturing whisky, and will give an idea of how much angels’ share there has been since the last regauge. Samples of the whisky can also be taken, to check on the development of flavour and take note if anything is awry. Imagine it as a sort of MOT for a whisky cask.

We recommend that casks are regauged every 3-5 years on average, just to make sure their maturation is progressing within expected parameters.


Regauged litres of Alcohol. This is the measure of how many litres of pure alcohol are present in the cask following a regauge. Comparing the RLA to previous RLAs and the OLA will inform the cask owner how rapidly their cask maturation is progressing, and how much the angels have taken. Knowing the accurate RLA is crucial for accurate labelling of a whisky bottle at the end of maturation.


An optional but exciting stage in the cycle of whisky cask ownership. Most newly distilled spirits are poured into American white oak (ex-bourbon) barrels or hogsheads. These infuse the maturing whisky with colour and certain flavours – especially honey, citrus and vanilla (your experience may vary).

Many cask owners, from the largest distilleries to the smallest independent bottlers can choose to impart new characteristics on their whisky by transferring the whisky from one cask into a new cask of a different size or type. This process is known as a re-rack.

Popular re-racks include Oloroso sherry butts, port pipes and virgin oak quarter casks. There are many more niche and interesting options, however. Cask maturation is still not a fully understood art, so it can be quite exciting to discover exactly what effects a new cask will have on a re-racked whisky. A regauge will be performed on a cask undergoing a re-rack.


There was a time when Spanish sherry was shipped to the UK in casks – this was a golden era when ex-sherry casks were plentiful for whisky producers to use. Two things have happened since sherry’s last heydey in the 1980s – first; Spain now sends us sherry already in bottles, second; sherry is no longer nearly as fashionable to drink as it used to be.

This means that sherry producers no longer use special casks for transport overseas. The sherry casks that we do get are purposefully ‘seasoned’ with sherry prior to being sent to Scotland, a process which keeps the sherry in the cask for a few weeks: just enough to prep the cask with sherry flavours to impart into any subsequent whiskies. These seasoning casks are modeled on the old transport casks that we used to get our sherry in.

This process gives options to aspiring whisky makers. It’s possible to season a cask with almost any kind of alcoholic spirit, wine or brewed product (the SWA does have some caveats), and create a re-racking cask that gives your chosen flavours to your whisky.

Teaspoon Blend

A very attractive name for a clever loophole. Since single malt whiskies have become prestige products, many distilleries want to keep their own single malts official and consistent. An independent bottler may buy a cask of whisky from a distillery, and mature it in way that the final product is different from what people expect of that distillery’s products. If they also release it under the same name, it could be ripe territory for confusion.

‘Teaspooning’ is the art of adding a mere teaspoonful of a different whisky into a full cask. Though it’s not enough for anyone but the most homeopathic whisky drinker to say that the original whisky has changed, even a teaspoonful of different whisky is technically enough to create a blended malt, which is no longer legally a single malt whisky, and thus not entitled to carry the name of any one distillery. The whisky industry is more permissive these days and teaspooning is no longer widely practiced – but stay on your toes.

Trading Names

Scottish distilleries have their own brands and intellectual property to think about, and for many of them this means controlling the kind of products that bear their name. No matter how delicious it is, a highly experimental whisky that diverges from the original style of the distillery is unlikely to be welcomed by the team responsible for brand control.

For this reason, some casks that are traded to third parties carry a trading name, which is common across the industry.  Importantly this doesn’t affect any naming rights for labelling purposes and so any future bottling of your cask can be labelled with “Speyside Single Malt distilled at Craigellachie”, for example, even though this cask is traded as ‘Blue Hill’. Other examples of this practice are; Whitlaw (distilled at Highland Park), Glenshiel (distilled at Glenrothes) and Duich (distilled at Tamdhu).

Always consult with our sales team about appropriate names for your whisky in the cask, and which euphemisms may or may not be necessary. It may be a chance to flex your creative naming muscles.


Samples can be drawn from the cask using many tools, but the valinch is the most traditional and glamorous. Essentially a large copper pipette, whisky is drawn inside and then can be transferred into sample bottles, with whisky flow controlled by a thumb placed over the end. No special training is needed to use one, so I hope you get to try it someday. Simple and satisfying, though unfortunately suggestive to look at.


An awkward acronym, this collection of letters refers to the Warehousekeepers and Owners of Warehoused Goods Regulations – documents that describe the necessary procedures when transferring whisky (and other duty suspended products) from one bonded facility to another. Regulations like these ensure that the transport of whisky is always done under the strictest scrutiny.

Patrick Costello
Director of Business Development, Cask 88

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