Almost a work of art: the construction of a Scottish pot still
The pot still is the centrepiece of every traditional whisky distillery. Its characteristic copper shape not only characterises the appearance of the distilleries, but also has a decisive influence on the quality and flavour of the whisky. Despite individual differences in design and size, most stills have common technical features that are essential for the distillation process. But how exactly is a pot still created and which structural elements are essential for its function?
Introduction to pot still distillation
The pot still is one of the oldest and most traditional methods of distilling whisky. It is mainly used in Scotland and Ireland and is known for its ability to produce complex and flavoursome distillates. In contrast to modern continuous distillation processes, distillation in a pot still is carried out in batches, which makes the production process more complex, but at the same time brings a distinctive character to the whisky. The combination of copper, heat and craftsmanship gives whiskies from pot still distillation their depth and individuality.
The pot still is the centrepiece of every distillery!
Our thanks go to Richard Forsyth from the coppersmith of the same name in Rothes, Scotland. He explained the basic design criteria of Scotch malt whisky stills to us years ago with great expertise. The Forsyths company has its origins in the production of stills and is now responsible for the renovation and maintenance of around 50 per cent of all stills in Scotland. At that time, only 12 experienced employees looked after stills. The majority of the workforce is involved in the manufacture and maintenance of equipment for the petrochemical and pharmaceutical industries.
Production of the still
The still is made from 99.85% pure copper (British Standard BS2570C106), using around 80% recycled material, including disused stills.
First, the copper sheets are cut into the required shapes and bent into the characteristic curved shapes using machine-driven hammers. Today, the joints are joined using inert gas welding - a more modern method compared to earlier riveted or soldered joints.
Hammering is not only used for shaping, but also for smoothing weld seams and solidifying the surface. Finally, the still is ground, polished and coated with protective varnish to achieve the typical copper-coloured surface.
Still bottom tray
Each still consists of an upper and lower bowl. While the lower part is technically adapted to the firing system, the shape of the upper part influences the flavour of the whisky. The lower bowl is a round copper pot still with a special base. In direct-fired stills, this is curved upwards to ensure a stable gas flame. The wall thickness is 16 mm for gas firing to withstand the high temperature (up to 650 °C). A rum bearing, driven by an electric motor, prevents the solid residues from burning on. It consists of a chain belt made of copper rings, which wears out after 2-3 years and has to be replaced. In indirectly heated stills, the base runs downwards in a cone shape to make it easier to drain the pot ale. In the past, spiral heating pipes were used, but these quickly became clogged. Modern heating cylinders prevent this problem and ensure more efficient vapour heating.
Heating stills
Conventional:
Until the 1970s, stills were usually fuelled with coal. Today, indirect heating with superheated steam dominates. Steam is channelled from a boiler via insulated pipes into a closed heating system. The vapour releases its heat, condenses and is reheated in the circuit. Only a few distilleries, including Glenfiddich, Glenfarclas and Macallan (wash stills), still rely on direct firing with natural gas. As the flames hit the copper directly, the rum leavers inside prevent the burning of solid grain residues in the wash (approx. 6-7% solids). Coal is no longer used for heating!
Nowadays:
Modern stills use several hollow heating cylinders through which hot steam enters from above and drains downwards as condensation. The wash flows in from below, is heated and rises to the top. Guide plates inside ensure even heat distribution.
Steam is supplied via a ring pipe, while ring-shaped collecting pipes collect the condensate. Spray heads are fitted for cleaning to prevent deposits. After distillation, a cleaning fluid is sprayed onto the cylinders, heated and then rinsed out.
As indirectly heated stills are exposed to less heat and abrasion, 6 mm copper wall thickness is sufficient for the boiler base and walls.
Still top
When a whisky connoisseur mentions the shape of a still, they are usually referring to the special design of the top. The shape of the top has a significant influence on evaporation, flow and condensation. The Lyne arm, i.e. the transition to the condenser, also plays a decisive role in the quality of the raw whisky.
During distillation, the alcoholic vapours rise in the neck of the still, condense on the cooled copper wall and flow back into the boiler. Only at a higher temperature do the lighter components pass through the bend into the Lyne arm and on to the condenser.
The four sections of the upper part:
- Cover (A): Spherical cover of the boiler.
- Intermediate piece (B)
- Neck (C): Cone-shaped connecting piece.
- Curved piece (D): Transition to the Lyne arm.
- Lyne arm (E): Conducts the vapours to the condenser.
Wall thicknesses and wear:
At 3-4 mm, the wall thickness in the upper section is thinner than in the lower section to enable the curved shape. Wash stills are usually 4 mm thick, spirit stills around 3 mm. The greatest wear occurs in the elbow and Lyne arm, as the hot alcoholic vapours dissolve copper molecules here.
Alignment of the Lyne arm: influence on reflux
The shape of the lyne arm significantly influences the reflux and thus the final flavour profile of the whisky. There are two main variants:
- Swan neck pot still: This classic shape is characterised by a curved neck with a bend reminiscent of a swan neck. The curved Lyne arm encourages a stronger reflux, favouring lighter, finer alcohol.
- Straight neck pot still: Here the neck runs straight upwards, resulting in less reflux. This allows more heavy, aromatic components to enter the distillate, resulting in a stronger, fuller character.
Condenser (heat exchanger) - crucial for distillate liquefaction
At the end of the distillation process, the condenser (heat exchanger) ensures the decisive conversion of the alcoholic vapours into liquid distillate. After the vapours have passed through the swan neck and the Lyne arm, they enter the condenser, where they are cooled and liquefied by a cooling system - usually using water as a coolant.
The condenser therefore plays a crucial role in converting the hot alcohol vapour into liquid form. The finished distillate is then channelled into the spirit safe , where the alcohol content is measured and the further distillation process is controlled.
Cooling with Worm Tub condensers
In the past, worm tubs were used to cool the distillate. The Lyne arm is simply continued as a pipe and placed in the form of a spiral in a tub filled with cooling water, which slowly cools the spirit.
As this system is maintenance-intensive and space-consuming, many distilleries now use shell-and-tube condensers, which are more compact and easier to handle.
Nevertheless, some distilleries, including Lagavulin (Islay) and Balmenach (Highlands), continue to use worm tubs. These influence the character of the distillate, as the increased copper contact and water temperature control produce a lighter, less complex raw spirit.
What influence does the pot still have on the flavour
The shape of the still has a significant influence on the flavour of the whisky. Tall, slender stills enable better separation of the flavours, as lighter alcohol rises more quickly and heavier, oily components remain in the kettle. This results in a mild, smooth whisky, as with Glenmorangie.
Smaller, squat stills, as with Lagavulin, make for a stronger, more intense whisky, as heavy flavours separate less easily.
Additional elements reinforce the separation:
- Constrictions in the neck, as in Glenkinchie's spirit still, calm the vapour column and improve the selection of flavours.
- Spherical protrusions between the lid and neck increase heat dissipation, promote reflux and enable finer separation of the lighter vapour components - a principle that Glenmorangie skilfully combines.
Service life of a still
A still lasts an average of 25 years before it needs to be replaced. Copper erosion caused by aggressive liquids and mechanical stress leads to a gradual reduction in wall thickness. Particularly affected are:
- The boiler of the wash still, where solid residues severely wear away the material.
- The upper part of the spirit still, which wears out more quickly due to hot, alcoholic vapours.
As the walls of spirit stills are thinner, their upper parts often have to be replaced after just 10 to 15 years. As a guideline: If the wall thickness drops to 50 % of the original thickness, replacement is necessary - otherwise there is a risk of technical failure of the still.
Myth debunked:
Contrary to popular belief, stills are not rebuilt with exactly the same dents and dings. A new still costs around 50,000 euros and nobody would deliberately damage it just to supposedly preserve the flavour. The actual flavour-defining factors lie in the shape, size and material - not in individual irregularities.
A pot still in use
If you want to find out exactly how malt whisky is distilled with such a still, visit the following page, for which we were once again able to recruit an experienced master distiller.
Conclusion
The pot still is a traditional still used in whisky production. It is typically made of copper and plays a crucial role in the distillation process by influencing the character and flavours of the whisky. In contrast to continuous distillation processes, the pot still allows for discontinuous distillation, resulting in richer and more complex flavour profiles. The shape and size of the pot still can vary and have a direct influence on the final product as they affect the contact of the distillate with the copper and the return of heavier vapours. Pot still distillation requires more effort and time, but is appreciated by many distilleries and connoisseurs as it produces whiskies with deeper flavours and greater complexity.
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