When we think of Scotch Whisky, on the surface it seems to be a relatively uncomplicated drink. But whether it is single malt, single grain or blended Scotch Whisky, there are a wide range of flavours and aromas that can be created from only three components or ingredients.
There are many ways we can influence the flavour and mouthfeel of whisky to create something as diverse as the drink we know as whisky. Everything from the way the barley is malted, the length of the fermentation, the copper contact in the distillation and of course, the type of cask used along with the length of maturation, all impact the flavour of the whisky that eventually reaches your glass.
Each part of the creation process has a distinct role to play in forming the drink we know and love. Not least of these processes is the ‘final stage’; maturation.
Maturing whisky is unexpectedly complex and is not as simple as putting distillate in a vessel and leaving it. In fact, the process can make or break a whisky: If you make a mistake with the cask and maturation then you may find that all the effort that has gone into making the spirit will have been wasted. This may not be found out until a few years later.
In this article we explore all the ways that a cask impacts your whisky. We start with the type of wood and end with ‘Finishing’ before summing up the what casks are used for when they can no longer be used for whisky. Read on, or use the navigation below to jump to your preferred section.
- How the Wood Type Used In A Cask Effects Your Whisky
- The previous use of a cask and what it means to your whisky
- How Many Times The Cask Has Been Used Before
- Toasting & Charring The Cask & What it Means for Your Whisky
- Why Cask Size Matters to your whisky
- How Warehousing & the Length of Maturation can shape your Whisky
- What does ‘Finishing Whisky’ mean?
- Alternative uses for exhausted casks
How the Wood Type Used In A Cask Effects Your Whisky
Casks used in the Scotch whisky industry by law have to be made of oak, but this can come from a variety of sources. The Latin name for oak is Quercus, and within this genus there are approximately 600 species of oaks worldwide. Oak is native to the Northern Hemisphere, with oak being found in North America, throughout Europe, parts of Asia and North Africa.
Predominantly the oak casks used in Scotch whisky make use American and European oak, often with casks that have been previously used in the Bourbon whisky and Sherry wine industries.
The main difference between oaks is down to the porousity of the wood. American Oak is denser and therefore will interact with the spirit less. American Oak also grows straighter and has less knots than European Oak making it easier to make into casks. Due to its relative higher porosity, European Oak will impart more wood influence, which includes spicy notes.
Differing oaks can be used in finishing. For example, in 1993, Glenmorangie released a series of whiskies that used different oak barrel varieties for finishing the whisky, and each had a different effect on the spirit. The American Oaks used were Missouri Oak, Burr Oak, Chinkapin Oak, Swamp Oak, Post Oak and the only European oak used in the series was the Truffle Oak which was from the Black Forest.
Ardbeg Kelpie, released in 2017, used Bourbon casks as well as Virgin Oak casks from the Black Sea coast. There are so many variations possible, as well as considering how long the spirit is finished for or if it has undergone full maturation in a certain cask type.
Overall the main impacts of the source of the oak on your whisky is going to be more woody influence from porous European oak while American oak is more common due to its more subtle influences and ease of working with when coopering casks and barrels.
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The previous use of a cask and what it means to your whisky
After we consider the type of wood that is used to make our cask, we then have to decide on what type of whisky we want and therefore what type of cask we want to put our spirit in. What the cask has held before will play a big part in adding colour and flavour to our whisky. The majority of Scotch whisky is either matured in a sherry cask or a bourbon cask, and both take advantage of the fact that the Scottish do not like things going to waste, and are very practical when things may be going cheap.
By US law, Bourbon can only be matured in a virgin cask, which means it is a cask that has not been filled with any other liquid. The barrel must be charred and in order to be called a ‘Straight Bourbon’ must be matured for a minimum of 2 years. Once the Bourbon has been bottled, there is no further use for the cask. Something that has only been used for under 5 years may still have another 60 years of life left, and therefore the enterprising Scots use it for maturing their whisky.
A similar situation used to happen for sherry casks. Sherry is a fortified wine made in the Andalusia region of Spain, centred around the city of Jerez. There are quite a few types of sherry with the Pedro Ximémez (PX for short) and Oloroso being the most common types of sherry casks used with Fino, Manzanilla and Amontillado also being available. Many people assume that the sherry casks used for whisky maturation were used for the production of sherry – this is not so. For centuries, sherry was a popular drink in the British Isles, and was easier to ship in transit casks – often made of European oak. This was because it was cheaper, and as the sherry would only be in them for a few weeks or months, it wouldn’t have much impact on the sherry. Once the sherry arrived in Great Britain, it would be bottled, and the barrel was discarded. Enter those canny Scots once more; they found a use for all these unused casks, and they soon discovered the impact it was having on their whisky too.
The sherry industry actually uses the solera system for ageing. It is a complex system of moving the liquid from barrel to barrel in a cascade. It is very important that these casks do not interact with the wine and this is why they are made of the denser American Oak. Solera casks have often been in use for many years, and have minimal reaction with the liquid in them and as such would be no use for the maturation of whisky.
The use of sherry casks has become more and more expensive over the years. This is mostly because in 1981 the Spanish Government changed the rules regarding sherry, and insisted that it was bottled in Spain before export. Furthermore, sherry drinking is becoming less and less popular, so there are not so many casks available. Some distilleries have overcome this by having their own cooperages in Spain and having partnerships with the sherry Bodegas in order to secure a source of sherry casks. However, it is most likely that the casks are only seasoned with sherry for a period of between 2 to 5 years. The sherry used for the seasoning will then most likely be used to make sherry vinegar or be distilled to make a sherry brandy.
Generally speaking, Bourbon casks generally give you creamy, lightly sweet caramel and vanilla flavours, along with a paler golden coloured spirit. Sherry casks give you a sweet, fruity, deep flavours, in particular dried fruit. Oloroso casks can also give a relatively drier taste, and both give you a deeper colour compared to Bourbon.
Of course, Sherry and Bourbon aren’t the only types of casks that can be used. Wine cask finishes are becoming more and more popular, with Cabernet Sauvignon, Chardonnay and Rioja being used, as well as fortified wines such as Port, Madeira, Muscat and Marsala also becoming popular. Rum is fast becoming a popular choice, with one example being the Balvenie Caribbean Cask 14-year-old. This gives a different type of sweet influence to the whisky, being more of a sugary sweetness. While some of these casks could be used for the complete maturation, it is more common for these to be used for finishing the whisky.
The Scotch Whisky Association (SWA) are slowly starting to change the regulations about what is an acceptable cask, and it is now possible to also get whiskies finished in Champagne, Cider, Cognac and supposedly there is a Tequila finished whisky on the cards. The SWA stipulate that as long as the cask that the whisky is matured does not make it taste more like the liquid in the finishing cask rather than whisky then there should not be a problem.
Glen Moray were amongst the first to challenge the SWA rules by maturing one of their whiskies in a Cider Cask. Glen Moray sell some of their old casks to Thistly Cross Cider in Dunbar, not too far away from Edinburgh. They are used to mature the cider there, and a good cider it is. However, they took some of the casks back and in 2018, a limited run of 2000 bottles were released of cider finished whisky. Their claim to get around the SWA rules at the time was that the cask had previously contained whisky in the past, and therefore didn’t break any rules.
How Many Times The Cask Has Been Used Before
Just because the Bourbon industry only uses its barrels once, it doesn’t mean that everybody else has to, and the Scottish Whisky industry certainly likes to get its value. You’ve probably heard of phrases such as 1st, 2nd or 3rd Fill, as well as Virgin Oak, but what does this actually mean?
The number of fills given on a cask refers to the number of times that a cask has been filled with whisky, and does not include the Bourbon, wine or spirit that was in it before. Bourbon is typically only matured for between 2-4 years which will mean that the cask will still have a lot of flavour left to give.
What type and age of cask you use will depend on how active you need the cask to be and how long you intend to mature the whisky. Virgin Oak casks will be the most active, as they only have been toasted or charred, and therefore will impart a very big wood influence on the maturing spirit. This means they are only really appropriate for short maturation periods or for finishing. Similarly, a first fill European Oak Sherry cask will be quite active, and the cask influence will overpower the distillery character. If a long maturation period is anticipated for the spirit, it may be more appropriate to use a 2nd fill cask. For even longer maturation periods, a 3rd fill cask may be more desirable.
As casks slumber in their warehouses, they are effectively breathing. Casks with more active wood will also enable more losses as the vapours move in and out. Initially, the spirit will be immature; too young to give a pleasurable experience. As the spirit interacts with the charred wood the char will act as a filter and start taking out the unpleasant compounds as well as allowing the spirit to interact with the compounds within the wood. This is known as subtractive maturation, the length of which may typically be 5-10 years.
When the spirit passes its immaturity phase, eventually the spirit will start to react with the wood to take on the flavours, this becomes what is described as additive maturation. A close eye is kept on progress, and eventually the spirit will reach a point where the distillery character and the cask character will combine to give the best taste, and this is when the spirit is ready for bottling.
If a cask is overactive, it will overpower the spirit before it hits the sweet spot and the distillery character is lost and is why a longer maturation period may benefit from less active casks. If any adjustment is needed to the spirit, it can be put into another cask for finishing.
Toasting & Charring The Cask & What it Means for Your Whisky
So far, we have looked at how the type of wood and what the cask held before may influence your whisky. The next thing that may influence your whisky is the amount of charring that is applied to the inside of the barrel.
When a cask is constructed, at a very minimum it has to be toasted. This is done by placing the barrel over a relatively light flame to seal the wood. This has to be done to every barrel as it stops the natural saps interfering with the liquid stored in the cask. In the case of wine, beer and cider, this is usually as much that needs to be done. However, Bourbon also requires the cask to be charred.
Charring is when the cask is subjected to a more intense flame for a short period of time. This gives a charcoal layer on the inside of the cask that often looks like an alligator skin and has a few purposes.
The main purpose is that charring opens up the wood and the uneven surface increases surface area within the cask for the spirit to react with. The charcoal works as a subtle filter in the cask, removing unwanted compounds like sulphur which can be created during the distillation process. Additionally charring alters compounds found in the oak so the char also influences the colour and flavour of the whisky while it matures over several years.
The compounds in oak casks
The oak contains 4 main compounds that will have a part to play in the flavour of our whisky; hemicellulose, lignin, tannins and lactones. When subjected to heat, hemicellulose starts to break down into wood sugars which caramelise on the inside of the cask, giving sweet flavours such as toffee or caramel. Lignin is responsible for vanilla flavours within the spirit, and is responsible for more woody and spicy notes as the char is increased. Oak lactones are commonly associated with woody and coconut flavours but their effect is lessened as the char increases.
Lastly, the compound that most people will be familiar with is tannins. Present in everything from tea to red wine, they are also present in whisky. The amount of tannin in the oak is reduced when the wood is being seasoned prior to being made into a cask. Tannins are important to the whisky maturation process. They add that dryness to a whisky and a certain amount of astringency. They also remove some of the sulphur compounds which aren’t always wanted in the spirit. Most importantly, tannins assist in the breakdown of lignin which will increase the flavour of the whisky.
In summary, all casks are toasted and some are charred. The degree of toasting or charring impacts the surface area of the cask, the rate of interaction and the eventual flavour profile of the cask
Why Cask Size Matters to your whisky
The interaction with the wood depend not only on the type of wood, the char levels and the previous liquid, but also on the size of the cask.
The larger the cask, the smaller the spirit to wood surface area ratio, and therefore the lower the amount of interaction between the cask and whisky. What that means for your whisky is the smaller the cask the shorter the maturation period, and consequently the larger the cask the longer the maturation period
Some common cask sizes associated with Scottish whisky production are:
- The American Standard Barrel is approximately 200 litres, and is used for bourbon.
- The hogshead is typically 250 litres. These are commonly made using the staves from recycled bourbon barrels, although larger rings and new ends are needed.
- Sherry butts or port pipes are 500-600 litres in size.
- Barrique barrels are used for wine, and are usually 250-300 litres.
- Puncheons are commonly 500-600 litres.
- Madeira drum are around 550 – 700 litres.
- The quarter cask is around 50 litres (quarter the size of a Bourbon cask)
Quarter casks are the smallest and as such they have the highest surface area for interaction between the spirit and the wood. This means quarter casks mature spirit very quickly, and may only be suitable for short maturations or for finishing.
Butts, pipes, puncheons and drums are the largest types of cask. They have the smallest surface area ratio for interaction between the cask and the whisky. Larger casks take much longer to mature the spirit and as such these types of cask are only suitable for long term maturation.
How Warehousing & the Length of Maturation can shape your Whisky
We come to the final points of how a cask can influence whisky, and that is the maturation itself. The type of warehouse can have an effect, whether or not it is a traditional dunnage warehouse with an earthen floor, providing cool, humid storage or an airier and more modern racked warehouse which allows more of an airflow around the barrels.
The location of the warehouse will influence the spirit within casks. For example, Speyside only has a couple of distilleries that can be described as coastal, such as Inchgower by Buckie, Roseisle close to Burghead or even Benromach in Forres, which is very close to Findhorn Bay. Spirit matured here will be influenced by the salt air from the Moray Firth, whereas your more inland Speyside whiskies such as Macallan, Tamdhu, or even Glen Grant will not have this influence. A cask matured close to the sea may develop maritime notes such as brine which tell so much about where the cask matured as the atmosphere surrounding it is absorbed by the wood.
The weather conditions will also play a part – distilleries such as Dalwhinnie, which have warehouses that are high above sea level (the highest in Scotland) will see a lot of cold, snowy weather, which will affect the rate of evaporation from the cask. The opposite is true for whiskies that are made in the hotter parts of the world such as India, where evaporation is much more of an issue thanks to the temperature and humidity of that region.
Even the position in the warehouse will make a difference. While a distillery can predict roughly the evaporation rate for a given climate and can have an idea of the final tastes within the whisky for a given type of cask, each cask and even its position within the warehouse is unique and thus can give an individual subtle flavour and aroma. A cask closer to a wall may well give a different taste due to subtly different conditions compared to a cask in the centre of the warehouse, similarly a cask at the top or bottom of a stack. For all but the most refined of tasters this difference will not be discernible.
The length of time that maturation takes varies. As noted previously even the size of cask can impact this, and however similar the process is no distillation is exactly the same each time because no cask is exactly the same and each cask sits in a different position in the warehouse. Therefore, each cask may become ready at different times for bottling.
To satisfy demand there is a trend towards younger whiskies at the moment (which is often hidden with non-age statement bottles) most whisky for single malt can be ready for bottling around the 10 – 12-year-old age.
If it is considered appropriate, and an extended maturation is desired, then the whisky may be re-racked into another barrel that is less active. This can allow whisky to mature for longer without the risk of the distillery character becoming overpowered by flavours from the cask and taking on excessive woody notes.
What does ‘Finishing Whisky’ mean?
Finishing a whisky is the practice of putting the whisky from one cask into another one for the final stage of its maturation. Often the finishing cask is of a different wood type or is a cask that has held other wines or spirits. It is often known as double or wood finishing. In some cases, the whisky may be put into a third or multiple casks.
The casks used for finishing will normally be first fill of a cask previously used to mature something other than whisky, but virgin oak casks can also be used. As first fill casks and virgin oak are very active then the finishing periods will be short – typically between a few months to around 2 years.
The casks used to finish a spirit will vary, but as mentioned before will usually be a wine or fortified wine such as Sherry, Port, Madeira or Marsala. It is possible to use casks that have previously contained other types of Whisky, Rum or Brandy. It is now becoming possible to use other spirits such as Mezcal and Tequila as mentioned earlier. A Swedish whisky distiller is also infusing their spirit with Green Tea leaves!
Why is finishing practiced? There are a couple of main reasons. It could be that a distiller is trying to create a new expression. A popular finished whisky would be something like Balvenie Doublewood which is initially matured in American Oak casks, but is then finished in 1st fill European Oak casks.
Another reason that finishing is used is that perhaps there are some casks that did not meet the expected quality and it is felt that there is no benefit to continuing to mature any further in the original cask. Of course, nothing is wasted and such a cask would benefit from a period of finishing to correct the spirit before it is bottled.
A benefit of finishing whisky is that it actually makes different casks available for longer maturation. For example, a 1st fill European oak wine cask will be quite active, and would not be the best for initially maturing your spirit. However, if the cask has already been used to finish another spirit, then this cask can then be used as a 2nd fill cask for longer maturations.
The Final Uses For a Cask
All good things come to an end, and the cask is no different. After first maturation the cask can get reused as a second or third fill, however this cannot go on indefinitely. After use as a third fill nearly every cask has nothing left to give; all the compounds and sugars in the wood have been exhausted, and can give nothing more to any whisky for maturation.
But that may not be the end of the story.
Casks have been used for centuries for vessels to store goods in, and while it may not be so prevalent now, a used whisky cask can still be re-purposed for such means. There is a coffee roaster based in Glasgow that uses former Auchentoshan and Laphroaig casks for storing coffee beans. This doesn’t give the coffee a whisky taste, but does give a lovely richness.
A very common retirement plan for old casks is that they get converted into garden furniture, or used for planters. Look around many of the railway stations in the North of Scotland and you will see planters made of whisky casks fashioned into wooden train displays.
Lastly, when a cask can be used for nothing else, its final destiny is for use as firewood. Because they are made of oak which is a hardwood, the resulting fire is more intense and longer lasting. Plus, there is the wonderful benefit that they burn while emitting a lovely whisky smell. If you are lucky enough to sit beside a whisky cask fire, as you sit and smell all the wonderful aromas, you can contemplate the journey that wood may taken from being an acorn in the forests of the USA, to the Sherry Bodegas of Spain through to the whisky producing powerhouse of Scotland, and finally to its end keeping you warm, ideally while you sip your favourite dram.
We hope that you have enjoyed the Romance of the Cask series. At the least we hope we have garnered you with some new knowledge, and ideally that we have instilled in you a new found respect for the cask and all the ways that is impacts your whisky from the wood it is made from to the size of the casks.
Mark Littler are experts in all things whisky, and whether you just interested in whisky, are thinking buying a cask or have a cask that you are thinking of selling then we can help. Just get in touch by emailing [email protected].
