What’s the Difference Between a Pot Still and a Column Still?
If you’re a shrewd imbiber, you may notice that some bottles of liquor — for instance, Irish whiskey like Redbreast — advertise a particular kind of still used to produce the spirit, in this case “single pot still.” Elsewhere, you may notice other bottles — like Japanese whisky Nikka — instead touting something called a Coffey still used to make their wares. If you delve deeper into these phrases, you might find that there appears to be a whole host of different kinds of stills: in addition to those above, you can find column stills, alembic stills, continuous stills, patent stills, and many others. What do all these terms mean, and how do they effect what you get in your bottle?
The pot still is what most of us think of when we think of a still: the stereotypical still design, made of copper, with a wide, bulbous bottom and a long, thin, tapered neck. There is evidence that pot stills made of terracotta were used as early as the 400s BCE, but the name you’ll see most attached to its invention is Arab alchemist Al-Jabir around 790 CE. At the time, Al-Jabir wasn’t looking to get tipsy; he was looking to bring out greater purity in his liquid materials to try and find the secret of eternal life. However, once it was discovered that water and alcohol have different boiling points, the pot still — also called an “alembic,” which is an alchemical term — starting being used to instead increase the purity of alcohol such as wine.
The way a pot still works is simple: the contents of the large lower chamber, called the pot, are heated until the alcohol vaporizes. The vapor travels up the long neck, where it is cooled down by cold water. Once cool enough, the vapors condense back into liquid, where it is collected in a separate chamber. Thus, you now have a product that has a much higher alcohol content, since most of the water in it got left behind in the pot. In the olden days, a pot was heated simply by lighting a fire under it; these days, vaporization is usually achieved with superheated steam, which is easier to control and fine-tune than fire, and which allows distillers to better guide their product. That said, the pot still is still fairly inefficient in terms of energy expended. Not all of the alcohol makes it into the collection chamber, and due to the fact that pot stills have to be batch operated — that is, that in-between batches, they have to be emptied, cleaned, and refilled — using a pot still is a laborious task.
Great men spent ages trying to increase the speed and efficiency of pot stills, and in 1831 Irishman Aenas Coffey patented his “Coffey still,” based on the use of two vertical columns instead of a single pot. Also known as a patent or continuous still, but best known these days as a column still, Coffey’s still behaves like a series of pot stills all linked together, stacked on top of each other. The liquid to be distilled falls through each chamber from the top of the column, while superheated steam comes up from the bottom. The steam vaporizes the alcohol, while the leftover “wash” with its alcohol removed falls down to the bottom chamber, where it is turned into steam and is used to vaporize the next batch. The vaporized alcohol floats up through each chamber of the column, and since each chamber has a lower temperature than the last, more and more impurities in the alcohol get left behind. The alcohol, with its low boiling point, gets vaporized and thus a purer concentration of alcohol is left behind in each chamber. The more chambers a column still has, the purer the concentration will end up.
Lest you start visualizing a column still the size of a skyscraper, know that a column still with an abundance of chambers will be made up of several interlinked columns; the alcohol will reach the top of one, and then get filtered into the bottom of the next, where the temperature is yet still a little cooler. This allows a column still to have an end product of 95% pure alcohol, as opposed to the 60% to 80% alcohol a pot still can end up with. (This doesn’t mean you’ll get a higher abv in the bottle of course, this is just the initial concentration. Alcohol from both pot and column stills are further watered down before bottling.)
So if column stills are so much more efficient and produce such a pure product, why would anyone make liquor in a pot still these days? The same reason why audiophiles might prefer a vinyl LP to a CD or MP3: those impurities in the distillate are what give the spirit its flavor, and a pot still allows its spirits a warmth and depth that the cold efficiency of a column still can’t match. A whisky or Cognac made in a pot still has the reputation of a private, personal, hand-made treat; sure it’s more labor-intensive, but that only means that you’re getting a superior product than something made in a detached, aloof column still, right? Many people certainly think this way. In general, the more rich and flavorful liquors — single-malt Scotch, Cognac, high-end rum, mezcal — are made in pot stills, while crisp clear spirits — vodka, white rum, gin — are made in column stills that can reach high abvs. The big exception to the rule is bourbon and rye whiskey, which are usually made in column stills, but often in a slower, more hands-on style like one might find with a pot still. Of course, exceptions to all of these rules of thumb abound.
Both pot and column stills have a permanent place in the history of spirits, and neither are going anywhere anytime soon. But at least now you know what each one is used for, and why.