Distillation is a very simple process for separating two liquids in a solution from each other, utilising different boiling points. In the same way as evaporating sea water leaves salt behind, so heating a low alcohol solution will allow the alcohol to evaporate whilst the water content remains.
By collecting and condensing the vapour as it evaporates, we separate out a concentrated alcohol.
The equipment used for distillation is known as a ‘still’, and can take many forms. Most will fit into one of two categories:
The pot still is the most basic type of still. Generally made from copper, it consists of a large copper pot sitting atop a heat source (usually gas nowadays), with a ‘swans neck’ at the top where vapour is collected. This pipe is usually cooled to encourage the vapour passing through it to return to liquid form, before being collected in a receiving cask.
Using a pot still for distillation is very time consuming and labour intensive, since only one ‘batch’ can be processed at a time, and the distiller must wait until the whole process is finished before he or she can empty the pot and begin again.
The continuous still is a more technically advanced piece of equipment, which allows a continual input of the low alcohol solution, whilst separating out the desired alcohol in a constant output stream. A ‘column’ element within a continuous still will see the vapour condensed and vaporised many times over, each time increasing its alcoholic strength, which allows this type of still to produce incredibly high abv spirit.
The economical advantages are obvious here, but in a classic quality / quantity debate, pot stills are still considered to produce the most flavoursome and characterful spirit.