A trademark of Caribbean rum production, double retort stills are essential to achieve the medium and heavy-bodied spirits adored by the world over.
A while back, I briefly explored the topic of dunder in rum production, specifically the difference between it and muck pits. While writing about dunder, I mentioned the role of double retort pot stills, sometimes called the Adams still, which were conceived in the early 19th century, and promised a more complete examination of the topic.
Rum can be made off of every type of still, including simple pot, single retort, double retort, and column. The double retort still, however, has come to define rum, specifically rum made in Jamaica. Mike Delevante began working at Appleton Distillery in 1963, and during his time there he operated both double retort stills and continuous stills, the introduction of which coincided with significant changes to the flavor profile of Jamaican rum. He now focuses primarily on consulting and designing stills for clients, including Still Austin in Austin, Texas.
To understand retort stills, you have to first be familiar with pot distillation, since a retort still is itself a kind of pot still. The most basic pot still has a simple construction: A base pot is connected to an onion or head, which sits atop its opening, which is in turn connected to a tube that slopes downward leading to a condenser.
Sometime around the 19th century, British expats in Jamaica decided to increase the efficiency of pot stills. Rum distillation had started a couple centuries prior on the sugar plantations of the Caribbean, supposedly in Barbados; slaves on the land were the first to discover that molasses was capable of fermenting into alcohol. The fermented material would then be distilled to remove impurities and concentrate the alcohol. Pot stills were used exclusively in the beginning, and though the earliest form of distillation had its advantages, there remain hindrances to the style, namely that a single distillation can only achieve a max ABV of about 45% when starting with a wash around 8-10%.
Distilling at least twice is necessary to achieve the desired ABV on a simple pot system, but it’s costly. The still has to be emptied and recharged for each run, consuming excess fuel to heat it again. The volume-driven aspect of the distilling business was as true back in the 19th century as it is now — even distillers 200 years ago realized that the time they spent preparing the still for a second run was money wasted. At some point, a distiller cleverly decided to connect the simple pot to a retort, which is where a weak alcohol distillate would be placed. Instead of going directly to a condenser, the lyne arm of the pot still would feed into the bottom of an additional pot called a retort. The vapors coming off the pot would travel through the retort, bubbling the weak distillate and depositing some of the more volatile congeners. The energy from heat would then evaporate the alcohol in the weak distillate found in the retort so that the final distillate coming off it would have a proof around 100.
This innovation was progress, but distillers will recognize immediately that a product with an ABV of 50% has left quite a lot of alcohol in the wash. In the early 19th century, Édouard Adam patented his own still, which was inspired in part by the Woulff Bottle, a common chemistry apparatus developed in Europe. Delevante explained that, “What he thought of is, why not transfer two retorts between the still and the condenser and it’ll be like distilling [the wash] three times because each retort acts as a small still, which instead of being driven by steam is driven by the vapor of a small pot.” This three-times distillation mimicked the way that Irish whiskey was made, Delevante told me, as well as early American bourbon whiskey.
The double retort pot still was a natural evolution of a simple pot with one retort. In an Adams still, the pot now had two retorts, one of which was filled with low wines while the other was fed with high wines prior to the start of distillation. A single run would begin about the same as it would with a simple pot still. The pot would be charged with fermented wash at about 8%, and the first and second retorts would already be filled with low and high-alcohol distillate, around 35% and 55-70% ABV respectively. These low and high wines were either leftover from a previous distillation or, in the instance of a first run on a new still, “the easy way to do it is to get some 35% alcohol that you’ve made somewhere else, and put that in the low wine retort, and get some 55% and put that in the high wine retort, and you get product immediately,” Delevante explained.
The still is heated by steam or some other fuel source, and as the temperature inside the pot rises, alcohol begins to vaporize. This vapor, averaging roughly 25% ABV, goes into the bottom of the first retort through a sloping tube where it will bubble up through the low wines and, as the water element condenses, release the alcohol present there. The vapor that comes out of that vessel, now at roughly 50% ABV, will then be delivered into a high wines retort in the same fashion. The vapors coming off the second retort can be rectified to roughly 85-90% ABV before being condensed back into liquid form through, most likely, a worm-in-tub condenser. These secondary and tertiary distillations, which occurred without manually running the low wines back through the pot still, were a precursor to the level of efficiency that we would eventually experience via continuous distillation.
Today’s rum distillers do not rely exclusively on pot or retort stills; they can have an assortment of pot stills, retorts, and continuous stills inside their facilities, which is the case at Appleton. Around the time that Delevante began working there, Appleton received their first column still and then, later on, a different type of continuous still. “We got a Coffey still that made a lighter rum, so Jamaica then started blending the light rum with the pot still rum,” Delevante said. Eventually, they added a three-column still to their roster, which they purchased with the intention of making vodka and gin. “We then had three types of stills to choose from: the three-column still, the Coffey still which made a light rum, and the pot still which made a flavorful rum,” Delevante continued. “So, in Jamaica especially, and other countries, there’s a blend of three different types of rum after they age it.”
The blend of spirits coming off different still types shifted the flavor profile of rums across the Caribbean. “Jamaica was the last to adopt the column still in the 1960s,” said Richard Seale, owner and distiller of Foursquare Distillery in Barbados. “It was very controversial in the anglophone Caribbean, but eventually blended rums won over much the same as blended whisky won over.” The introduction of continuous distillation cemented blended spirits as the norm throughout the region and is now by far the most common kind of rum available. As Seale said, the use of a combination of stills became “the heritage of Barbados Rum production. Column stills never replaced [double retort] stills; they were added, and blended rums were made. Barbadian rum blenders came to accept the column still but see the [double retort] still as indispensable.”