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How is Whisky Made

How is Whisky Made

“How is whisky made?” Is a question I get asked a lot, and it is a question I try to answer briefly and tend to fail miserably as my wealth of knowledge spills out of me in a deluge of facts, caveats and interesting asides. This article therefore, is my best effort at conveying the most pertinent facts, and has been distilled (if you pardon the pun) from a first draft that was close to fifteen pages of typed text. I hope you enjoy it, or at least come away from reading knowing a little more than you did when you started.

Defining Whisky

Whisky is an alcoholic product that has been made of grain, distilled, and then aged in barrels.

This is the most basic definition.

Different countries have different guidelines for each stage of the process on local levels and for local products.I shall be focusing on Scottish whisky and Irish whiskey, those being what we primarily deal with at CaskCap. Though I am sure I will write about bourbon and other world whiskies at a later date.

Barley and Grain

Barley and Grain

The grains of a cereal are its seeds. These seeds store sugars as starch so that they have the energy to grow new plants.

The amount of different cereals used in the making of whisky is called the mash bill. If the mash bill contains 100% malted barley that whisky is a single malt.

If there are other grains on the mash bill that is classified as a grain whisky, with a specific exception in Irish whiskey.

Irish Pot Still whiskey is produced in the same fashion as a single malt but the mash bill has to contain a minimum of 30% unmalted barley, as well as the malted barley, and can contain up to 5% other grains, typically rye and oats (Not to be confused with 80s pop sensation Hall and Oates). Irish Pot Still, also known as Single Pot Still is a category unique to Ireland and is protected by a European GI.

Barley is the key cereal for whisky making in the British Isles. Barley is favoured for its flavour, and because it contains enzymes that convert starch into fermentable sugars. 

The other most common grains in whisky are wheat and maize (corn) these are suited to making mass production grain whiskies. The decision whether to use corn, wheat or a mixture of both is usually dictated by market price. 

Rye is becoming a more popular distilling grain, especially in Ireland. Rye has a unique aromatic quality, as well as pleasant bready and spicy flavour. 

Malting Floor


Yeasts, which are the microbe that makes alcohol, cannot ferment starch so it is important to convert starches into usable sugars. 

The malting process forces germination on a grain. This process is the first stage of plant growth and so the barley grain.

  • forms a root and a shoot
  • Exposes starch granules to enzymes
  • Starts breaking down starch into simple sugars. 

The stages of malting are as follows:

  1. Steeping:

    The barley grains are soaked in water, drained, soaked in water and drained again over a period of 1-2 days. This mimics rainfall in natural growth and tricks the grain into starting germination.
  2. Germination:

    Barley grains are transferred into a warm area, (usually a large box or drum) where they grow under controlled conditions. The drums will rotate, or the boxes will have a turner built in that stops the growing roots from matting. Traditional floor maltings will have the barley laid out on the ground and someone will turn the grain by hand using specialty shovels. 
  3. Kilning:

    Germinated barley grains are then put into a large oven and “cooked” with hot air to kill the grain and stop the germination process. It is at this point that peat (partially decomposed plant matter, traditionally burned as a fuel) can be burned which is what gives certain whiskies their signature smoky flavour. 

    In Scottish and Irish law, the grain sourcing and the malting process does not have to happen within the country. But all further production steps do. Distilleries that source all of their grain locally are a rarity, and in a market that is fast becoming more aware of authenticity and sustainability, it is seen as a desirable and more premium quality for a distillery. 



The barley is ground down to a flour, then that flour is then pumped into a big container called a mash tun and mixed with hot water. Traditional mash tuns mix the mash using spinning mechanical rakes to churn the grain bed. Modern mash tuns use fixed blades to cut through the bed and allow drainage as well as assisting in mixing the water and grain. This process extracts the sugars from the grain and gives the distiller a sugar rich liquid that can then be fermented. This liquid is called wort.


The wort is cooled down in a heat exchanger and then pumped into washback, which are made of either wood or stainless steel. Washback is the name for the container where fermentation takes place. Wooden washbacks give more flavour to the fermentation but stainless steel is more efficient to clean, and some distilleries do not want the flavours imparted by wooden washbacks. Yeast is then added to the wort and the fermenting liquid is then called wash. The wash is left for a minimum of 24 hours, but industry standards are anywhere between 50-120 hours. Short fermentation gives malty cereal notes, as seen in Glenkinchie’s single malt, and longer fermentation gives floral, fruity and creamy notes, as seen with Deanston, with even longer fermentation becomes very tropical fruit heavy as shown in Glenallachie. 

The fermentation process gives a beer (called wash in Scotland) that is about 8% ABV. Almost all distilleries use distillers yeast, but a few of the more craft distilleries are starting to experiment with other yeast types in fermentation. 


Distillation at its simplest is like boiling a kettle, you heat up the wort at the bottom of the still, it boils into a vapour and the alcohol that comes out the top of the still, known as the swan neck, can be aged into whisky. 

Distillation works because water and alcohol have two different boiling points. Alcohol boils at 78.3°C and water boils at 100°C.

A pot still is made up of three key parts:
The pot - where the liquid is put in and heated
The swan neck - where the vapours are refluxed
The lyne arm - which connects the still to the condenser

The wash is then put into the first pot still (called a wash still) and heated until the alcohol starts boiling off. The alcohol leaves the still and the distiller collects it as low wines with a strength of 21-30% alcohol. The second distillation is pretty much identical to the first, but the still is usually smaller, and is called the spirit still. The second distillation takes the spirit to over 70% alcohol. 

If a third distillation is used then the end result will be between 80-90% alcohol.

 Spirit coming off a still is clear and colourless, it leaves the still as a vapour, so to turn it back into a liquid it has to then go into a condenser. 

The two main types of condensers are: worm tub and shell and tube. The worm tub is the traditional form of condenser and consists of a coiled copper pipe (the worm) and a barrel full of water (the tub). The worm tub has less copper contact with the spirit which can allow more sulphur taint to get into the final product. In small amounts sulphur can give a meaty flavour but if too much gets through then aromas and flavours of rotten eggs can materialise. Shell and tube condensers consist of hundreds of narrow copper tubes surrounded by flowing water for efficient heat transfer and lots of copper contact.

This clear spirit is called New Make Spirit, or British plain spirit.

There are a few aspects of distillation that affect how the new make tastes.

I won’t mention every aspect of still design and operation that will make a difference, but it breaks down into two key aspects.

These are: The purity of the alcohol, and the copper contact.

Aspects of the still that increase reflux, or the number of times the alcohol boils and condenses, will effect the purity. The more reflux the more pure a spirit is, so the smoother it tastes but the less complex flavours the spirit has.

Copper contact is mostly affected by the size and shape of the still. Copper reacts to many of the undesirable compounds present in the wash and removes them from the final spirit. The most important of these compounds to remove is sulphur, which gives eggy and struck match aromas and flavours. 

Clonakilty Distillery


All new make spirits that want to be whisky must be put into a wood barrel and aged for a minimum of 3 years before it can be called whisky. The impact of wood ageing accounts for much of whisky’s flavour and almost all its colour. The flavour also comes from raw material, fermentation and distillation processes. 

In Scotland whisky can only be aged in oak wood. The main kinds of oak used by distillers are American white oak and European oak. Irish whisky law states that whisky only has to be aged in wood barrels so we are starting to see more experimentation in Ireland with other species of wood such as hickory, chestnut and maple.

The reason that European distillers have so much access to American oak is because the American bourbon industry has to use a brand new barrel every time. This makes American oak relatively inexpensive and plentiful. European oak predominantly comes from the sherry industry, but wine barrels are becoming more common as consumer tastes change.

Casks are stored in bonded warehouses.

The bonded warehouse types are as follows:

  • Dunnage, a single story low stone structure with dirt floors, barrels are stacked 3 high by hand and stay at a very consistent cool and humid climate year round. 
  • Racked warehouses, large buildings made of brick, concrete, or steel with a solid floor, barrels are stored horizontally eight to twelve layers high and are placed there by forklifts and elevators. 
  • Palletised warehouse- much like a racked warehouse but casks are stored vertically on specialised pallets and braced together and stacked up to eight layers high, palletised is  the most efficient form of storage. Storing casks vertically also decreases the wood contact between the spirit and the cask, which slows down the ageing process and allows for longer ageing. 

The previous contents of the cask, for example using ex port, beer, or tequila casks, can also have a large impact on the flavour of whisky, which has made using these specialty casks to ‘finish’ whisky for short periods with intense new flavours are increasingly more popular. 

Warehouse of Casks for Maturation


Once the whisky has matured it then needs to be bottled to reach the market. 

There are two key kinds of bottlers for casks of whisky. These are the distillery themself (official bottling) or an independent bottler. 

Most whisky is bottled by the distillery as an official bottling, these make up the distillery's core range of offerings and consist of barrels of the same age, or cask type, blended together and bottled in bulk to be sold to supermarkets and bars for the mass market. These bottlings consist of many casks and make up the majority of the market.

Unique casks, ones of particular quality or with unusual finishes tend to be brought to market by independent bottlers. Independent bottlers are companies that buy and bottle casks but do not produce any whisky themselves, this means they do not tend to have a core range that they always produce but instead bring casks of particular quality or interest to market. They tend to sell direct to consumers or sell through specialty retailers and tend to command a higher price per bottle than official releases and are often seen as of higher quality. 

Grain whisky in brief.

Grain whisky: Grain whisky is made in a different way. When making grain whiskey the grains are cooked instead of malted and then distilled in a column still. Column stills are tall towers containing many plates that allow the separation of spirits from water to a much more precise degree, the spirit is removed at the plate where the ABV is the desired strength and these stills can be run continuously so are much more cheap and efficient than pot stills, which have to be filled and emptied every run. However column stills don't create as flavourful a spirit as pot stills. 

This is not an exhaustive insight into production, detail has been left out and there are exceptions to every rule to be found somewhere in the industry. But as a primer it should suffice.

About the author

Sam Thompson is a 24 year old whisky obsessive. Alongside experience working in whisky retail in Scotland, he has a WSET level 3 in spirits and a foundation in distilling from the IBD. When not writing about Whisky Sam can be found cooking, reading, attending the Opera or local jazz club, or surfing in his native Cornwall.