Pot still


A pot still is a type of distillation apparatus or still used to distill flavored liquors such as whisky or cognac, but not rectified spirit because they are bad at separating congeners. Pot stills operate on a batch distillation 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.
Spirits distilled in pots top out between 60 and 80 percent ABV.
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 is filled about two-thirds full of a fermented liquid 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, such as aldehydes and esters. Alcohol has a normal boiling point of 78.4 °C, compared with pure water, which boils at 100 °C. As alcohol has a lower boiling point, it is more volatile and evaporates at a higher rate than water. Hence 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 it 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 whiskies are only distilled twice.
During distillation, the initial and final portions of spirit which condense 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, or other congeners.

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 and is no longer in use. As of 2014 the largest pot stills in use are coincidentally located in the neighbouring New Midleton Distillery, County Cork, Ireland, and have a capacity of.
Components of a traditional pot still: