The Evolution of the Pot Still in Scotland by Iain Russell, Part 1

Scotch malt whisky can only be distilled in pot stills: it’s stipulated in the Scotch Whisky Regulations, 2009. This traditional type of still has been used for centuries to make whisky in Scotland and its image has become an iconic symbol of the country and its culture. But although the stills have changed little in outward appearance over the years, they and the methods of working them have evolved and been improved upon by generations of distillers. 

As the name suggests, pot stills were originally fashioned from cooking pots or cauldrons, into which the distiller filled wine or ale and then heated to ‘boil off’ the alcohol. In Scotland, these pots were originally made of metals such as cast iron, tin or copper. A simple lid or ‘head’ was fitted on top to capture the alcoholic vapour that rose up from the warming liquid and the head was attached in turn to a spout, or ‘arm’, which conveyed the vapour to the opening of a tubular metal coil, or ‘worm’, encased in a barrel of cold water. The alcoholic vapour passed along the arm into the worm, where it cooled and condensed, returning to liquid form and dripping down to be collected in a cask or other receptacle below. Typically, the first distillate had to be redistilled at least once to achieve the strength and purity required by the distiller.   

Until 1781, individuals in Scotland were permitted to use stills of up to 10 gallons capacity (reduced to 2 gallons in 1779) to make spirits for private consumption without payment of duty and private distillation in small stills was reportedly widespread. Excise records of prosecutions and still seizures confirm that the practice of private distillation continued for long after its prohibition! 

Copper is well-suited for a boiling pot: it transmits heat evenly, reducing the danger of the furnace overheating the base of a metal pot and scalding the solids in the liquid within to produce harsh, unpleasant flavours. The metal is easy to work, which made it an attractive choice for the manufacture of heads and worms. However, copper was expensive and less wealthy ‘private’ distillers sometimes preferred to have their stills fashioned from tin. In addition, while copper reacts with volatile compounds in the vapourised alcohol to remove unwanted sulphurous notes and produce a milder spirit (a little-understood benefit at the time), these reactions also cause the formation of verdigris, which was known to add a green tinge to the distillate and was suspected to be harmful to health. Many of the large distilleries working in the Scottish Lowlands in the 18th century were equipped with tin-coated arms and worms to protect the copper surfaces and reduce the time required for cleaning.   

Drawings by John Leven, General Supervisor of the Excise in Scotland, showing a conventional pot still alongside a typical flat-bottom still adopted by Scotland’s Great Distillers to increase the rate of spirit production. From Reports of Committees Upon the Distilleries in Scotland, 1798.   

The earliest distilling utensils were made by local tinsmiths, blacksmiths and pewterers. For example, it was reported in the late 18th century that, after Islay lairds confiscated their tenants’ small stills and banned whisky-making on the island during a period of grain shortages, the distillers invited tinkers over from Ireland to make new ones they could use illegally. But some coppersmiths began specialising in still-making when the whisky industry grew in scale and there was a growing demand for their services. The surviving business records of Robert Armour, a Campbeltown plumber and coppersmith, provide an invaluable record of the business activities of an early specialist whisky still-maker, recording his sales of stills and other utensils to hundreds of small-scale distillers in and around Kintyre and Arran in the 1810s.

Distilling became a major industry in the Scottish Lowlands during the 18th century and the very large commercial distilleries of the Haigs, the Steins and the other ‘Great Distillers’ introduced one of the first and most significant innovations – some might say deviations – in still design. Responding to changes in the way in which the Government calculated duty from 1786 – basing it upon the production capacity of a still rather than the quantity actually produced – these distillers installed wide, shallow and flat-bottomed stills which were designed to expose a greater surface area to heating and a greater liquid surface area from which the alcoholic vapour could rise to be collected. The new-fangled stills were fitted with rummagers – iron chains which were agitated by means of a spindle to prevent the yeasty and other vegetal matter in the liquid at the bottom of the still from scalding and imparting harsh, burnt flavours.  

These and other innovations permitted the rapid working of the stills – some could be charged and discharged under 10 minutes, it was claimed, where in the past a still might be worked only a couple of times a day. Greater rates of production permitted enormous savings in Excise duty but there was a significant impact on quality, with many observers complaining that spirit from the rapidly-heated flat stills was harsh and acrid, suited only for rectification for gin, or for consumption by the most undiscerning drinkers.   

An intriguing aspect of rapid distillation arose from the problem of foaming: when the still was heated rapidly, froth from the boiling wash rose up in the pot, overflowing over the arm and contaminating the spirit being collected from the worm. To prevent this, many distillers resorted to a traditional practice, adding soap to the wash to reduce the surface tension of the liquid and break down the foam.  This practice continued well into the 20th century: at Ardbeg in the 1920s, for example, there were regular deliveries of white curd soap, which was introduced into the wash via a soap box fitted to the still. Distillery veteran Alan Winchester remembers distilleries still using soap to prevent foaming in the early 2000s, and that the soap boxes at GlenDronach were only removed in 2008.    

While the great distillers experimented with shallow flat stills, domestic distillers in the Highlands and in rural areas of the Lowlands continued to make use of conventional pots, distilling a mash of malted barley heated slowly to produce a less fiery and more palatable spirit. The ending of taxation based on still capacity (as well as the opprobrium of the more discerning whisky drinkers) eventually persuaded the Great Distillers to abandon the flat-bottomed stills, and to seek to improve on the design and methods of working the conventionally-shaped pot still. The scene was set for some radical innovations in the 19th century… 

Iain Russell is an acclaimed whisky historian and author, recognised for his expertise in the heritage and traditions of Scotch whisky.