When we talk about a pot still, we refer to one of the most basic forms of stills and one of the most widely used ones as well. A pot still refers to a copper pot still, sometimes also referred to as an alembic still or arabic still. The name Alembic is derived from the Arabic ‘Al-anbiq’, which is the Arabic word for a still. The earliest designs of stills and the history of distilling lies in the Arabic world so it’s quite natural that we refer to copper pot stills with their original name.
A pot still relies on the basic principle of alcohol distillation and its design is simple yet effective. It consists of a single pot, usually round and somewhat bell shaped, that tapers towards the top which results in a long thin tube that curves down, known as the swan neck. This is the point where the vapours are being collected and slowly condense into liquid again. This swan neck then moves downwards and ends up in a spiral or coil, usually submerged in a vat with water to further cool the liquid.
These stills can be as small as 5 litres, or as big as 75.000 litres. The biggest pot still ever in history had a capacity of over 140.000 litres! No matter the size of a pot still, the technique of distillation and its working principle remains the same.
There are multiple reasons as to why these still have been made out of copper in the past and are still being made out of copper today, even though copper is quite an expensive material. Historically, copper was relatively cheap and easy to work with and could be found in nature. It's easy to bend and hammer into shape. Secondly, copper conducts heat extremely well, meaning that you don't need a lot of fuel to bring the still up to temperature and you could start distilling with a very small heat source. After heating, it would also cool down very quickly, all things considered very useful in a process that relies on temperature differences.
They soon found out that spirits made in copper had a better quality and a much cleaner taste. This is because of the chemical reactivity of copper. Copper has antibacterial and antifungal properties and helps clean the fermented liquid of the yeast. Secondly, copper filters out volatile components such as sulphur, which could have been created during a bad fermentation process. All in all, copper has great qualities which helped produce better tasting distillates.
Because of all these reasons, distillers still use copper pot stills today. However, because copper is quite expensive, some producers are also opting to use pot stills with a copper lining.
Because of the shape and construction of a pot still, liquid can only go through this process once during a single run. During distillation, liquid turns into vapours and back into liquid again and then this is being collected. In order to get higher abv’s and stronger concentrations of alcohol, producers can choose to do multiple runs to further purify and increase the amount of alcohol in their final product. This is what’s referred to when something is ‘single distilled’, ‘double distilled’ or ‘triple distilled’. It refers to how many times the liquid has gone through the process of a copper pot distillation.
Due to the shape of the still and the curving of its walls, there is something happening which is known as ‘reflux’. Meaning that the heavier components hit the walls and reflux back into the pot, and get either redistilled or won’t ever reach the top and swan neck. This results in only the lighter vapours reaching the swan neck to cool down and be collected. However, this process is not foolproof and copper pot still liquids are still considered to be heavier and oilier in taste and mouthfeel after distillation in comparison to alternative styles of distillation such as column style distillation.