Rum is a category that truly stands out with rich history and diverse profiles. Almost dauntingly so! Aspiring distillers and new distillery start-ups have a lot to delve into to fully appreciate the full scope of art and science involved in rum distillation.
This article demystifies some of the complex still designs involved and some of the specific methods used in rum distillation.
Whether you are aiming for the robust flavours of a heavy rum or the refined nuance of a lighter variant, this introduction will guide you through some of the initial considerations to mull over, and explain the equipment typically used and why.
Understanding rum distillation types
At a simple level, the major factor differentiating various rum production, is whether it’s a batch or a continuous distillation process. Each method profoundly impacts the rum’s flavour, aroma, and overall character.
Batch distillation with pot stills
This traditional method, often associated with craft distilling, uses pot stills and is well-suited for producing rums with distinct, robust flavours and a rich bouquet of aromas.
Just like with whisky, the shape and size of the pot still will influence the character of the rum, with large pot but short stumpy necks typically producing a heavier spirit, compared to those with tall necks, that might produce a naturally lighter distillate.
Continuous distillation with column stills
For distillers aiming to produce lighter, more consistent rum profiles, column stills are the preferred apparatus. The multiple plates or trays in the column still enable precise control over the separation of alcohol and congeners, leading to a cleaner, lighter rum, typically distilled to a high abv.
When set up for continuous distillation, this still design is more efficient than batch distillation and is conducive to large-scale production.
Key elements to understand between the two:
The choice between batch and continuous distillation dictates a rum’s flavour profile. Pot stills tend to produce rums with deeper, more complex flavours, while column stills yield lighter, cleaner profiles.
Batch distillation suits smaller, artisanal operations, whereas continuous distillation is ideal for larger-scale production.
Pot stills require a lower initial investment but might have higher operational costs. Column stills, while more expensive to set up, offer efficiency and consistency in large-volume production.
Pot still distillation: Crafting heavy rum
In pot still distillation, the distiller must first carefully manage the heating rate, ensuring that the wash is heated slowly and evenly. This controlled approach helps in the proper vaporisation of alcohol and congeners, contributing to the rum’s rich flavour.
Just like with whisky, pot distilled rum is distilled twice. Initial distillation from a fresh batch of molasses typically yields an ABV of around 30-35% ABV. A second distillation is therefore carried out in order to attain the necessary ABV – typically between 75-90% ABV.
Once the distillate begins to flow from the still – understanding and managing the cut points is the next challenge. In both distillations, the distiller will separate the ‘heads’, ‘hearts’, and ‘tails’. Just as with whisky or brandy, this is particularly important on the second distillation.
The heads contain volatile compounds and are usually discarded or redistilled. The hearts are the core of the distillate, rich in flavour and desired alcohol content. The tails, containing heavier alcohols and oils, can also be redistilled.
Often, 5-10% of the charge of the still is made up of re-cycled heads and tails.
Precise cuts ensure a balanced flavour profile and high-quality spirit. A careful selection of how much heads and tails to recycle vs how much to simply discard is also important. It’s not just a case of what tastes the best, but a balance to build complexity and maximise yield.
Congener management
Congeners are compounds other than ethanol that are produced during fermentation stage. These substances include small amounts of chemicals such as methanol and other alcohols (known as fusel alcohols), acetone, acetaldehyde, esters, tannins, and aldehydes.
In pot still distillation, managing these congeners is essential for flavour development. The congener that most rum distillers talk about openly on are esters. By comparison, Scotch Whisky “peat freaks” as they call themselves, tend to focus on phenols. There’s a lot more to rum than esters – but it get’s the lion’s share of attention, and talk, making it something that’s worth fully understanding.
Heavier rums are characterised by a higher concentration of esters, which contribute to the rum’s aroma and taste.
Therefore, in order to craft a rum that resonates with the desired flavour profile, the distiller must balance the retention of beneficial congeners (like esters, phenols, lactones and fatty acids), while also removing the undesirable ones (like methanol, for obvious reasons).
Column stills: Producing a lighter style
Column still distillation is the most efficient way to produce a light rum. These stills consist of multiple columns, each with several plates or trays, which allow for a finer separation of the alcohol from the wash.
It’s worth noting that not all column stills are continuous. Especially in the craft sector. Many lighter rums are often made for bulk, but it’s possible to find batch process column stills (just as you do for vodka) and smaller craft producers using them.
The design and number of columns can vary. Some setups include a stripping column to remove alcohols and a rectification column to purify the spirit. Others simply involve a tall tower with 30+ plates.
Understanding the complexity of these columns is the main part of producing a consistent and high-quality light rum. For those operating column stills, the key element is less about congener management, and more about rectification.
A note on rectification
Rectification is the process of refining the spirit by removing unwanted congeners. In column stills, this is achieved through the multiple plates within the columns, where vapours condense and re-vaporise, allowing for a cleaner spirit.
The final alcohol by volume (ABV) levels in rum can be precisely controlled in a column still. Higher ABV levels result in a lighter rum with fewer congeners and a more neutral flavour. Lower ABV levels, on the other hand, allow for a richer flavour with more congeners.
This precise control over ABV is instrumental in defining the character and taste of the final product.
From rum to neutral spirits: The role of continuous distillation
In the transition from crafting rum to producing neutral spirits, continuous distillation comes into play. Neutral spirits are characterised by their lack of distinct flavour, achieved through a rigorous distillation process that has reached an end ABV of 95% (or over 96% ABV in the EU). Continuous column stills are ideally suited for this, as they can operate non-stop and produce a consistent product.
A huge amount of neutral spirit is produced from molasses. See our article on Continuous Distillation for more on this.
Advanced rum specific apparatus
Double retort and triple pot stills
The double retort system, often used in conjunction with a pot still, provides a method for a more refined distillation process. This system allows for a second and third distillation in situ, leading to a more concentrated and flavourful spirit.
This technique and still design, mostly associated with Caribbean rum production, enhances flavour complexity while also being quite energy efficient. Key features include:
- A double retort system consists of two additional chambers (retorts) connected to the main pot still. After the initial distillation in the pot, the vapours pass through these retorts. Each retort contains a liquid from a previous distillation, typically the tails, which are re-distilled when the vapours from the main pot pass through them.
- This process allows for a more thorough extraction of flavours and congeners from the wash. As the vapours interact with the liquid in the retorts, they pick up additional flavours and complexities, contributing to a richer profile.
- The double retort system is also energy-efficient. The heat used for the initial distillation in the pot still is effectively utilised for the subsequent distillations in the retorts, maximising the energy input.
- Distillers can manipulate the contents of the retorts to influence the final flavour profile of the rum. For instance, adjusting the proportion of tails or other liquid remnants in the retorts can lead to different flavour outcomes.
While double retort stills are geared towards crafting rums with enhanced flavour and complexity, there is also another rum specific still that is used for the opposite reason. Barbet Stills are ideal for producing light, clean spirits with minimal congeners.
Barbet stills
The Barbet Still, named after its inventor, is a type of column still designed to minimise the accumulation of unwanted congeners. It’s particularly useful for producing light rums and neutral spirits.
The unique design of the Barbet Still allows for a very precise separation of alcohol and congeners, resulting in a cleaner, more refined spirit. Think of it as a custom designed column still ideally suited to rum making. Here are some key aspects:
- The Barbet Still is a type of column still with a unique design that enhances the separation of alcohol. It typically features a series of perforated trays, each contributing to a more precise distillation process. The design allows vapours to rise and condense multiple times, effectively separating purer alcohol from heavier, unwanted compounds.
- One of the standout features of the Barbet Still is its ability to separate unwanted congeners, such as fusel oils and other heavier alcohols. The design allows the distiller to draw these unwanted parts off at a different point to where the distillate will be taken from. This results in a cleaner, more refined spirit – essential for producing high quality light rums!
More than the sum of its parts
Mastering rum distillation involves a deep understanding of the base material (your wash) and the compounds that it contains. This is then married up to the technical aspects that define how your still operates. Once you combine the two, you can start making great rum.
The reason discerning drinkers pay particular attention to still choice, it’s design and the details is not due to a copper fetish. It’s not about making lists to play top trumps for ester counts. It’s because it all builds towards why something tastes the way it does. The sum of the parts combine to far more than simple addition.
Any distiller looking to build their understanding of the category has a lot to learn. Each still will affect the potential flavours that can be made, the ABV yield and the process required to achieve quality outcomes.
More importantly, distillers need to understand how each still type taps into the spirit’s rich heritage in a completely unique way and if they want to subvert that, or build upon it.
