Beverage alcohol has been around for approximately 1,000 years and while there have been countless discoveries and innovations surrounding the distillation process during that time, the basic techniques have largely stayed the same. Early distilling practices were essentially batch distillations, performed in simple pot stills using a process arguably not too dissimilar from the modern methods of today’s great single malt whisky producers.
Batch distillation in the hands of an experienced distiller can produce incredible whisky, but it does come with some issues. It is labour intensive, often energetically inefficient, requires skills that are difficult to learn (and teach), and produces relatively low volumes of alcohol. As whisky continued to grow in popularity over centuries it was only a matter of time before someone stepped in to address these issues. Enter Aeneas Coffey.
During the early 1800s Coffey was serving as a Customs and Excise officer in Ireland. His job involved ensuring that distillers were operating legally and paying the required excise taxes to the Irish government. As a result, he was put in close proximity to the art of whisky distilling and knew the process as well as anyone. He had witnessed efforts by other inventors at creating a more efficient still design for the production of whisky, though none of those early inventions really took off in the industry. However, he did see the potential for a continuous column still design that could produce large amounts of whisky consistently and efficiently. Tweaking and refining designs from some of these earlier inventors, Coffey was able to finally patent his self-titled Coffey Still in 1830. Capable of producing more than 2,000 gallons of whisky per day, his design forever changed the way the whisky industry (as well as other spirits) operated. The Coffey still was arguably the first true continuous column still of the modern era and while the underlying physics of alcohol distillation remain immutable, the still itself behaves in a vastly different manor than the traditional pot still.
In a pot still a discrete volume of fermented wash is distilled completely. Afterwards the dealcoholized liquid in the pot is drained, new fermented wash is pumped in, and the whole process begins anew. This process is also known as batch distillation. In a continuous column still, the process is – as the name suggests – continuous. Outside of periodic maintenance or labour scheduling breaks, the still is constantly having fermented wash pumped into it with condensed distillate emerging on the other side. Speaking with Kyle Grant, project manager at Vendome Copper & Brassworks, he points out that these stills provide huge benefits to the busy whisky maker. “A continuous system requires minimal supervision, runs consistently and predictably, and has a significantly smaller footprint than a pot still of equal capacity, allowing for more efficient use of resources and space.”
A column still is composed of one or more towers with distillation plates or trays placed at specific intervals inside. A stream of preheated fermented wash (the ‘feed’) is pumped into the column somewhere in the midsection onto the feed plate. Live steam is fed into the column from the bottom and travels upward, eventually coming into contact with the fermented wash. The steam volatilises (evaporates) components of the wash such as flavour compounds and the all-important ethanol, which continue to travel up in the column in the form of vapour. The heavier components of the wash continue downwards, exiting the still as ‘bottoms’.
As the vapours travel upwards through the column, they make contact with each successive plate. In a way, each plate behaves like a batch still in miniature, with more volatile compounds continuing upwards while heavier, less volatile compounds reflux and fall down the column. To aid in this reflux system, the top of the column often has some form of precondenser with coolant flowing through it. This helps to set up a temperature gradient throughout the column with plates nearer the precondenser being slightly cooler than the ones below. So, the more plates within a column still, the greater the temperature gradient and therefore more reflux occurs, forcing larger amounts of compounds to fall out and be removed from the final spirit. The very lightest of compounds, such as toxic methanol that would be found in the heads fraction on a pot still, are removed through the highest plate in the column while the product or spirit plate allows distillate to flow out through a condenser a few plates down.
Continuous column stills sometimes get an undeserved reputation for removing too much flavour. True, the purest-tasting vodkas of the world are produced on column stills, but so are most bourbons (hardly a neutral spirit). It all depends how the column is designed and run. Chad MacIssac of Specific Mechanical Systems says, “As equipment manufacturers, we appreciate the unique interpretations of whisky character from person to person. We can build a distillation system with customer-requested design characteristics, to produce a distillate with the character desired by the distiller. We offer continuous column still designs that allow a distiller to ‘fine tune’ congener concentrations in the final product. This gives distillers control over the character of their final product in a similar way to batch distillation.”
Despite the consistency of product quality and greatly improved distillery throughput, the venerable continuous column does have a few drawbacks for some people. They tend to be quite expensive in the initial purchase, and while their footprint is often small for the volume they produce, these stills are usually very tall – Jim Beam’s stills, for example, reach around 65 feet (20 metres). Grant at Vendome concurs, “Continuous columns’ biggest major drawback is, unequivocally, height. When talking to people considering what style of distillation system to choose, height is almost always what first changes the conversation to pot still systems. Lack of flexibility is another one that comes up quite a bit… if people want to experiment with really high- or really low-proof whiskeys, a continuous system will not accommodate willingly.”
Despite these issues, there has been growing use of continuous columns across the whiskey space, including smaller craft producers. Peerless Distilling in Louisville, Kentucky notably uses a 26-foot (8-metre) column with a 14-inch (36-centimetre) diameter. Hard Truth Distilling in Nashville, Indiana has also installed a 14-inch column still from Vendome with 18 plates to produce its whiskies. This still will allow Hard Truth to make up to 40 barrels of whisky per week.
When Coffey patented his still nearly 200 years ago, he probably had no idea how important it would become to the whisky industry. The continuous column still is arguably one of the most important innovations to come along for whisky, sitting right alongside the charred oak barrel in its impact. These imposing structures of distillation science produce everything from delicate grain whiskies destined for the world’s great blends to heavy-charactered bourbons and ryes. They truly are a distillation marvel.