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A pot still is a type of distillation apparatus or still used to distill alcoholic spirits such as whisky or cognac. Pot stills operate on a batch distillation basis (as opposed to a Coffey or column stills which operate on a continuous basis). Traditionally constructed from copper, pot stills are made in a range of shapes and sizes depending on the quantity and style of spirit desired.
Contents
By law, cognac, Irish and Scotch malt whiskies, and single pot still whiskey must be distilled using a pot still.
Method of operation
During first distillation, the pot still (or "wash still") is filled about two-thirds full of a fermented liquid (or wash) with an alcohol content of about 7-12%. In the case of whiskey distillation, the liquid used is a beer, while in the case of brandy production, it is a base wine. The pot still is then heated so that the liquid boils.
The liquid being distilled is a mixture of mainly water and alcohol, along with smaller amounts of other by-products of fermentation (called congeners), such as aldehydes and esters. Alcohol (ethanol) has a normal boiling point of 78.4 °C (173.12 °F), compared with pure water, which boils at 100 °C (212 °F). As alcohol has a lower boiling point, it is more volatile and evaporates at a higher rate than water. Therefore, the concentration of alcohol in the vapour phase above the liquid, is higher than in the liquid itself.
During distillation, this vapour travels up the swan neck at the top of the pot still and down the lyne arm after which it travels through the condenser, where is cooled to yield a distillate with a higher concentration of alcohol than the original liquid. This distillate, called "low wines" has a concentration of about 25–35% alcohol by volume.
These low wines can be further distilled a second time in a pot still to yield a distillate with a higher concentration of alcohol. In the case of many Irish whiskeys, the spirit is further distilled a third time. However, Cognac and most single malt scotch whiskys are only distilled twice.
During distillation, the initial and final portions of spirit which condense (termed the heads and tails respectively) may be captured separately from that in the centre or "heart" of the distillation. This is because these portions of the distillate may contain high concentrations of methanol (which is toxic), or other congeners (which it may be desirable to keep out of the final distillate for reasons of style or taste).
History
The modern pot still is a descendant of the alembic, an earlier distillation device.
The largest pot still ever used was located in the Old Midleton Distillery, County Cork, Ireland. Constructed in 1825, it had a capacity of 31,618 imperial gallons (143,740 L) and is no longer in use. The largest pot stills currently in use are coincidentally located in the neighbouring New Midleton Distillery, County Cork, Ireland, and have a capacity of 75,000 L (16,498 imperial gallons). Components of a traditional pot still: