The Pot Still is the granddaddy of modern stills. But just because its old, that doesn't mean it isn't still relevant. Many distillers still choose to use a pot still instead of the more modern column stills, this is due to some key advantages the pot still has over its modern counterparts.
A Little History
The Pot Still is a type of distillation apparatus used to separate two liquids through boiling. Pot Stills are generally made completely or partially out of Copper.
The earliest known distillations were performed by the Akkadians in 1200 BC with the aim of making perfumes. The stills used for this purpose would have been quite straightforward, pots with curved necks and some form of condenser at the end. The first clear records of alcohol distillation come from 9th century Iraq, where Arab chemist Al-Kindi documented the distillation of wine.
It is also from this region and time, that pot stills saw a significant advancement in technology and thereby took on the familiar form we think of today. Jabir ibn Hayyan, also known as Geber or Al-Jabir, was an Arab alchemist in search of the Philosopher’s stone. At the time it was widely believed that distillation was the key to creating the legendary substance. The pot stills of the time were not able to create very pure distillates and so Al-Jabir set out to change that.
After much experimentation, he discovered that by adding an additional section to the top of the pot, the distillate came out purer. The final shape he settled on was something akin to an onion, this shape allowed him to achieve purity levels that were unheard of up until this point. He named this new still, Al-Ambiq, no known as the modern day Alembic pot still. The design quickly spread to Europe and became widely used in chemistry and alcohol distillation.
How It Works
At its most basic level, a pot still is just that, a pot. The substance you are trying to distil is placed in the pot, for example a molasses ferment. The pot is then heated, traditionally this was done with fire, but modern pot stills use steam-heated jackets. The molasses ferment heats up and when it reaches around 65 degrees Celsius, the first alcohols begin to evaporate, this is because alcohol has a lower boiling point than water.
These alcohols travel into the tube at the top of the pot, also called a swans neck, which then runs through a condenser, often cooled by water. Because the tube in the condenser is cooler than the vapour, that vapour then turns to liquid and at the end you collect liquid alcohol. With such a basic pot still, the alcohol coming out would not be very pure, meaning that some water would evaporate at the same time and the final liquid would be a mix of alcohol and water.
When distilling with an Alembic pot still, the final alcohol purity is significantly higher than with a basic pot still. This is because of the interesting onion shape on the top of the pot, not only does it look good, it also has a very important function. With the separate chamber above the main pot, a difference in temperature is created, cooler in the top section and warmer in the bottom. When the alcohol vapour rises from the main pot into this alembic section, the reduced temperature causes it to condense back into liquid.
In essence this is causing the alcohol to be redistilled over and over again. This happens until it reaches a high enough temperature in the top chamber for the alcohol vapour to go “over the bend” in the swan's neck to the condenser. Because of this redistillation effect created by the Alembic pot, the final alcohol distillate has less water and thus a higher purity.
While the Alembic pot still, and the different variations of it, are able to achieve a higher alcohol purity, they can not come close to the purity levels of a column still. So, if that is the case, then why do modern distillers still use pot stills for spirits like whiskey and brandy? The answer is simple, but also very important; - flavour!
Column stills separate the alcohol into different fractions, this results in a smoother product and one which comes out with a higher alcohol content. However, this is often at the cost of flavour. The advantage of a pot still is the fact that it does not separate the alcohol into fractions, resulting in greater flavour in the final spirit. Because of the trade-off between flavour and smoothness, pot distillers will often turn to barrel ageing to help smooth out the product before bottling.
In the end, our aim as distillers is to create a great tasting spirit, and while very important, the still type you choose isn't the only factor that determines if your product is good or not. Thus, it is not a debate between which is better, pot still or column still, but a decision about which works best for you and the spirit you are aiming to create.