Start a conversation about many of the world’s beloved spirits — bourbon, single malt Scotch, mezcal, or rum — and the subject will quickly turn to ingredients and aging. Distillation, on the other hand, is often overlooked, even though it is one of the most impactful aspects of spirits production.
The varieties to know are pot and column distillation, named after the stills in which they take place. Their fundamental processes are the same, though there are important differences to understand. Here’s everything you need to know.
According to the Scottish Whisky Association, distillation using pot stills was well established in the country by the end of the 15th century. But pot stills’ design is an evolution of an earlier device, the alembic, used for alcoholic distillation since the 9th century.
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Column stills, also known as patent, continuous, or Coffey stills, became common during the first quarter of the 19th century. Scotsman Robert Stein is credited with one of the earliest designs, which Aeneas Coffey, an Irishman, later improved.
Pot stills look like kettles. The “pot” refers to the large, spherical main chamber, from which a swan neck and lyne arm protrude like a spout. The arm feeds into a coiled condenser, also known as the worm, and finally into a collection vessel.
Column stills are more industrial-looking than pots. They’re often much taller than pot stills and contain multiple chambers stacked on top of each other, sometimes reaching several stories high.
Pot stills are almost always made of copper. Column stills, on the other hand, can be copper or stainless steel, and occasionally a mix of the two. Stainless steel columns usually contain copper elements inside the still, as the metal is essential in removing sulfur, which adds sour flavors to the distillate.
Distillation creates a high ABV spirit by evaporating ethanol from a fermented alcoholic base liquid (sometimes called a wash). Ethanol boils at a lower temperature than water, so it can be drawn off as vapor while water remains in liquid state. The process never makes pure ethanol, and the distillate always contains a proportion of water, as well as flavor- and aroma-giving compounds called congeners.
During pot distillation, the wash heats in the main chamber until boiling ethanol vapor rises to the head of the still and exits via the lyne arm. From here, vapor passes into the cooling coil, where it condenses and flows as a liquid into a collection vessel.
Traditionally, distillers used direct heat sources like fire to heat the pot, but nowadays, temperature-controlled steam is a common alternative. The modern technique is desirable because it reduces the risk of burning the wash, creating undesirable flavors. Yet some pot distillers continue to use direct heat.
Column distillation works like a series of pot distills taking place on top of one another.
In this process, the heat source (steam) exists inside the still, running from the base through its many chambers, and up to the top of the still. Wash enters near the top of the column and sinks down through the chambers in liquid state. As the ethanol heats and evaporates, it rises back through the chambers, condensing and re-evaporating at each stage.
In each of the chambers, ethanol loses impurities like water and congeners before it finally reaches the top of the still in a very pure form. From here, the ethanol vapor exits, passing through a cooling condenser and into a collection vessel.
Advantages and Disadvantages
Column stills allow continuous distillation, meaning they’re capable of drastically higher production than pot stills, which require cleaning after each batch. Column stills also provide a purer, cleaner distillate than pots, though pot stills produce a more flavorsome spirit, richer in congeners.
Spirits distilled in pots top out between 60 and 80 percent ABV (after multiple distillations), while columns can reach an ABV of up to 96 percent.
Because pot stills produce a more flavored distillate, they’re favored for producing spirits like single malt Scotch, Cognac, mezcal, and rhum agricole. Column stills, on the other hand, are preferred for neutral spirits, like gin and vodka, and are also often used in bourbon, brandy, and white rum distillation.