SPIR4100 - Technical guidance: Stages of production: Pot Still Distillation

A visual illustration is shown in the Pot Still distillation diagram (PDF).

Spirit is normally distilled from the wash by distilling it twice or in some cases three times. Two pot stills are used - the 'wash still' (1) and the 'lowwines / spirits still' (5). These stills are usually heated by means of internal steam coils though there are still a few sites where the stills are heated externally by means of a coal fire.

The wash is first pumped into the 'wash still' (1) and slowly brought to the boil. The more volatile alcohol vapours are driven off, rising up the neck of the still through a pipe called the lyne arm, and then into a coiled pipe called the 'worm' or 'condenser' (2) where the vapour is condensed back into its liquid state. This liquid flows through a secure viewing box called the 'low winessafe' (3), where it is monitored for strength and quality, then into the low wines and feints receiver (4).

This first distillation of the wash produces a distillate called 'low wines' and has an alcohol content of around 25%. For the second distillation in the low wines / spirits still (5), the low wines are mixed with the re-cycled products of previous runnings of the low wines stills. The condensate from the second distillation is carefully monitored by the stillman at the 'spirit safe' (6) as it is this run which produces the quality spirit that will eventually be sold to the consumer.

The first spirits off the still are the 'foreshots' or 'heads'. These spirits (approximately the first 15% of the run) are not considered drinkable and are diverted to the “low wines and feints receiver” (4) for further distillation.

The next 15% (approximately), which is produced after about twenty minutes of distillation, is the 'middle cut' or 'spirit'. This spirit is collected in a vessel called the 'spirit receiver' (SR) or 'intermediate spirits receiver' (ISR) (7) until the strength drops to 60% abv. The average strength of the spirits collected in the SR will be 68 - 73% abv.

When the strength of the spirit falls to 60% abv it is diverted to the low wines and feints receiver (4) to mix with the foreshots and low wines that are already there. This part of the spirit is known as the 'feints' or 'tails' and accounts for approximately 40% of the run. The mixture of low wines, foreshots and feints will form a new charge for distillation in the next run of the low wines still.

The final 30% of the run known as the 'spent lees' remain in the still to be discharged as waste.