Still life
Our writer asks rum producers what happens inside their pot stills
Depending on your aesthetics, a pot still is a beautiful sight: all that gleaming copper, curvaceous shapes and a neck ascending proudly. It’s a shame we can’t also see what’s happening within, though even if a camera could be operated inside a pot still the numerous reactions that take place would hardly all be visible. At least the changes that occur are evident when comparing what goes in, to what comes out of a pot still.
“I’m a pot still girl,” says Joy Spence, Appleton Estate’s celebrated master blender. “I love the funkiness of it, and it’s just so complex and intriguing.”
Distillation is a natural focal point, but each stage of the production process also depends on its predecessors. Without fermentation providing the right opportunities, distillation wouldn’t be able to achieve what it does.
Fermentation sounds simple enough: adding yeast to a sugary liquid based on molasses or sugarcane juice. The sugars provide an ‘all you can eat’ buffet for yeast cells, which gorge to grow and reproduce. But there is another consequence, as metabolising (‘digesting’) sugars results in yeast cells emitting a residue into the surrounding liquid, which is alcohol and various flavour compounds. “Fermentation is where you really set up all your flavours, which you can retain and refine during distillation,” says Leon Swallow, senior distiller at the Cotswolds Distillery, which produced its first rum in June 2018.
This fermented ‘wash’ has an alcoholic strength of around 8-10% ABV and is distilled twice in a pot still, though each distillation has a different objective. “The first distillation raises the alcoholic strength and removes a lot of the unwanted compounds, as well as water, allowing for a more refined and precise second distillation,” adds Swallow.
The vital element that enables distillation is heat, which usually means conducting steam through coiled pipes positioned in the boil pot (base) of the pot still. The temperature of the charge (i.e. liquid being distilled) gradually rises, and alcohol begins to evaporate at around 78ºC and ascend the neck of the still.
“I’m a pot still girl... I love the funkiness of it, and it’s just so complex and intriguing”
Different flavour compounds also have their own volatility (boiling point), with lighter, fruity compounds being physically the smallest and lightest, vaporising at lower temperatures. As the temperature continues to rise during distillation, progressively richer, more complex flavour compounds, which are physically larger and heavier, also begin to boil and vaporise.
This includes sulphur compounds, which form during fermentation. Although present in tiny quantities they are very assertive, being pungent and vegetal, and they ‘mask’ lighter notes such as fruit and sweetness. However, when sulphur compounds come into contact with copper in vapour form, a matrix on the surface of the copper ‘absorbs’ the sulphur compounds. Lowering the level of sulphur compounds reveals ‘lighter’ notes such as esters (fruitiness), as well as sweetness, which in turn changes the balance of flavours.
Contact with copper can be increased by slowing down the rate of distillation. All this requires is for the flow of steam through the coils to be reduced, the equivalent of turning the volume down, which slows the process and sees the vapours lingering for longer in the neck.
Nelson Hernandez, master distiller at Venezuelan producer Diplomático Rum, says, “We distil slowly to ensure the maximum copper contact, which lowers the level of sulphur compounds.”
When vapours reach the top of the pot still they are conducted to a condenser, in which the vapours condense back into liquid form. As a dedicated life-partner to the pot still, the usual style of condenser is a ‘shell and tube’, referring to a large jacket (shell) that contains numerous copper tubes positioned vertically. Cold water enters the tubes at the base, ascends to the top, and exits the condenser. Meanwhile, vapours enter the top of the condenser; as they meet the colder temperature of the tubes they condense, and liquid descends along the length of the tubes. Draining from the base of the condenser, the distillate collects in a spirit receiver (vessel).
The first distillation is a case of ready, steady, go, and keep going until the wash has been distilled, which yields a spirit with a strength of around 25% ABV. This spirit is not usually assessed, though the second distillation is all about constant assessment. When distillation begins the alcoholic strength of the spirit quickly rises, peaks, then begins to decrease. As the alcoholic strength changes so do its characteristics, and the balance between them.
This explains why the second distillation is divided into three consecutive phases: the foreshots (also known as heads), followed by the spirit cut, and finally the feints (also known as tails). The foreshots and feints have an unsuitable character and quality, and are collected separately from the spirit cut, which yields the resulting rum.
“We constantly nose the distillate coming over. The heads have a distinctive, pungent smell, and when fruity, floral aromas appear in the distillate we start collecting the spirit cut. The heads take about five minutes, we collect spirit for about eight hours and then the tails take about one hour,” says Hernandez.
Each distillery has its own individual house style, whether an elegant, fruity style, or a richer, fuller-bodied number. Swallow at the Cotswolds Distillery says, “We wanted to create an authentic rum with depth and character. The resulting distillate shows ripe fruit, including pineapple and bananas, together with caramel and also a taste of molasses, as we wanted to retain a sense of the original ingredient.”
An ultimate example of a pot still rum is the Hearts Collection of rare pot still rums recently released by Appleton Estate. Spence explains, “It’s a collaboration I did with world-class rum aficionado and collector Luca Gargano, and comprises three 100-percent single marque proprietary rums collected from our Appleton Estate inventory. Each vintage (1994, 1995, 1999) comprises a single proprietary marque distilled in a pot still produced by Forsyths and aged between 21 and 26 years. There are only 3,000 bottles of each marque. We named it Hearts Collection to pay tribute to where it was crafted, in the heart of Jamaica, and because the pot still uses the heart of the raw materials.”