Sugar Cane Harvest
As we detail in our guide to What Is Rum Made From, rum is made from sugar cane. Its harvest is a yearly process in the Caribbean but sometimes more in South America. As sugar cane is a variety of grass, it regrows when cut.
Few sugar cane plantations undertake the harvest by hand. Traditionally, this was done with machetes. However, the industry is largely mechanised today.
The sugar cane is then crushed or pressed to extract the juice. As you’ll also learn in the guide linked above, the resulting sugar cane juice is then either directly fermented or first converted in molasses.
Fermenting Sugar Cane Juice
Old Sugarcane Press
The distilled sugar cane juice for rum is made from what is called a “wash”, which first has to be fermented in order to produce alcohol. The cane juice or molasses is mixed with water and then introduced with yeast. The yeast will then consume the natural sugar in the molasses or juice and convert it into alcohol.
Occasionally, but rarely, rum producers will use naturally-occurring wild yeast. Yet, this is a much longer and complex process. For instance, “dunder” is a yeasty foam that forms during fermentation. In Jamaica, it is removed from a finished wash for the next batch of molasses.
Different strains of yeast work at various speeds and may also result in distinct flavours. Fast fermentation produces a lighter wash that tends to be favoured in white rums.
Meanwhile, darker rum merits a slow and careful fermentation where yeast is gradually added. The rate at which yeast consumes the sugar will also be affected by various minerals.
Slowing the process also allows for the development of congeners, flavourful compounds that consist of esters and aldehydes. As a result, it produces a thicker, more acidic wash, which can help towards richer-tasting rum.
How Rum Is Distilled
Once the sugar cane juice has been sufficiently fermented into a wash, it is ready to be distilled into rum. Distillation is a varied and complex process that may incorporate a range of different approaches.
While different producers may have their own cultural or individual techniques, distilling rum usually consist of either a combination or one of the following:
You can either use the links above to jump ahead or scroll down to read about them both.
Rum Copper Pot Stills
The traditional alembic is an Arabic invention that was introduced to Europe following the Umayyad conquest of Hispania during the 8th Century.
Although it had undergone many improvements before it was introduced to the Americas during the Spanish Conquest, the approach is still used for distilling sugar cane juice into rum.
A copper pot still works by heating low-proof alcohol in what is essentially a large kettle covered by a head called an “ambix”. As alcohol has a lower boiling point than water, it turns to vapour while water remains liquid at the right temperature of around 78°C.
The vapour will then rise through a long tube in the ambix, which cools and condenses it back into a liquid.
Good rum produced from a traditional copper pot still requires a significant level of skill. Although it provides the master distiller more control, only a small portion of the distillate is safe for consumption.
Indeed, a single distillation run consists of the following yields:
- Foreshot: The first 5% of distillate that contains some of the most toxic and volatile impurities such as methanol.
- Heads/High Wines: Distillate with volatile compounds such as acetone.
- Cut/Heart: Consisting mostly of ethanol, the most palatable part of the run.
- Tails/Low Wines: The least volatile components consisting mostly of thin-tasting fusel oils.
Usually, the parts of the heads and tails are recovered as “feints” and then redistilled in a future batch. In most cases such as with cognac, the heart requires a second distillation to remove impurities. As a result, it may also remove the flavour compounds, which are called “congeners”.
The Adam Rum Copper Pot Still
Many copper pot stills for making rum employ a concept that was invented in the early-19th century by Édouard Adam. The French distiller sought to improve the traditional copper pot still by introducing additional pots called “retorts”.
As a result, the stills would save time by avoiding additional runs while preserving the congeners as well as reducing waste by increasing yields. These two retorts would be connected one after the other after the ambix condensation tube.
The first retort would recover the low wines from the alembic’s wash while the second condensed the high wines. When distilling the mash, the retorts would already contain the low and high wines as feints. The resulting distillate was rich and flavour and achievable in a single distillation.
Although it was a failed project in Europe and quickly overshadowed by the Coffey column still in the 1830s, his invention coincided with a sudden growth in domestic sugar beet production.
Overwhelmed by a market crash and crippling debt, sugar refineries in the French Caribbean turned to rum distillation and the latest technology available was the Adam pot still.
Therefore, it’s no surprise that the Adam pot still is particularly prevalent among French-style distillers today. Distillers have developed their own techniques with the Adam still, which may consist of adding wash or dunder to the low wine retort to modify the flavour of the rum.
Similarly, some retorts feature chilled heads to create reflux, which forces the vapour to condense and fall back inside before being heated again.
However, the Adam still also used by some English-style producers in the Caribbean as well. Interestingly, it can also be found in some parts of Scotland for making whisky. Nevertheless, they may both also employ a Coffey column still during the process.
Column Rum Distillation
Inspired by the Adam still’s approach to fractional distillation, the continuous column still was invented by Aeneas Coffey is are generally far more widespread in the spirits industry.
Yet, despite having been invented in the 1830s as mentioned above, it wasn’t commonly used until 1852 when steam technology was capable of producing higher temperatures.
Unlike pot stills, column stills aren’t operated in batches and don’t require multiple runs. Furthermore, they produce much stronger alcohol, which in turn means that they produce more rum after it has been diluted to around 40% ABV.
As the name suggests, it consists of two towering columns called the rectifier and analyser. The analyser is essentially a series of pot stills in the form of perforated copper plates that have been stacked on top of each other in a long vertical cylinder.
Sugar cane wash is fed into the analyser where it is heated into steam. As the temperature is lower at the bottom of the column, only strong alcohol will be able to rise to the top and condense inside the analyser.
Meanwhile, the impurities that would make up the heads and tails autonomously reflux and condense as they come into contact with plates at different heights.
As a result, continuous column stills can produce alcohol as strong as 95% ABV. Meanwhile, the rum distillate from a single alembic pot distillation will rarely be above 60% ABV.
How Rum Is Aged
The ageing process is a key step to make rum. Indeed, every type of rum must be aged for a minimum period before it can be bottled. While Mexico permits as little as eight months, the legal minimum for most Latin American territories is two years.
Rum can be aged in either stainless steel vats or oak barrels. Stainless steel is usually reserved for white rum to prevent it darkening but it may also spend time in oak to produce some flavours and colour.
Casks For Ageing Rum
Typically, rum is aged in American white oak ex-bourbon whiskey casks. Since bourbon must be aged using new oak, used barrels are easy to acquire. Additionally, previously used barrels impart their flavour on the rum while also having a milder wood influence.
Furthermore, aged rums can be matured in other barrels previously used for alcohol from different countries:
- Cognac Casks: Charred barrels made from French Limousin oak.
- Sherry Casks: Spanish sherry casks made from American oak.
Sherry casks are particularly diverse with producers using casks that had been used for sherries like Pedro Ximénez, Olorosso, Fino, and Manzanilla. As there are no particular regulations, master blenders have the freedom to use any oak barrels according to the flavours that they wish to create.
As can be expected, there is a correlation between the territories and the barrels that they opt to use. Unsurprisingly, French-style rum tends to use cognac casks whereas Spanish-style rum may have a preference for sherry casks. However, it’s far from exclusive.
Nevertheless, ex-bourbon barrels are by far the most popular choice for the majority of aged rums. Other types of barrels tend to be used for finishing the ageing process.
Furthermore, the number of times the cask has already been used will also have an effect on the rum’s resulting flavour. Similarly, some Spanish-style may also make rum by ageing it using the Solera System.
Sistema Solera Rum Ageing
Originating in the Iberian peninsula, the Solera System is best known for making sherry, Madeira, and some French wines like Muscat or even Lillet. However, it is also used to age dark rum.
Rums like Zacapa and Cartavio are famous for using solera ageing and the process is deeply ingrained into their respective identities. The solera process consists of several levels of oak barrels that are filled with rum on top of one another. At fixed intervals, the barrels on the bottom row are partially emptied.
Afterwards, the barrels are refilled with the rum stored in the row above them. Usually, there are multiple levels so the rum will trickle down from the top to the bottom. The remaining barrels at the top level will then have younger rum added to them to ensure each one is full.
As a result, the oldest rum is at the lowest level whereas new rum is added to ensure the system is topped up. During each interval, rums of different ages will mix together and marry their flavours.
Therefore, the rum is continuously blending while it ages. The rums extracted from the bottom barrels may be up to a quarter of a century old. However, they will contain trace amounts of younger rum as well.
As it’s quite a confusing topic, we suggest watching Santa Teresa’s motion design video on the topic, which explains quite clearly.
How Long Is Rum Aged?
There are many factors at play that will decide the period time rum spends ageing. It doesn’t just depend on the type of rum made but the desired results as well as the climate.
Needless to say, dark rum is aged for longer than white rum. The latter usually spends the minimum two-year period in a combination of steel and wooden barrels.
Dark rum production can greatly vary. Firstly, territories with hotter climates will experience an accelerated Angel’s Share. This term refers to how distilled alcohol evaporates while it ages. For reference, Scotch whisky experiences a 3% annual loss whereas it is nearer 6% in the Caribbean.
As a result, it will also mature three times faster in the heat. Similarly, less time is available to let it continue ageing!
Meanwhile, maturation takes longer in milder climates. Although it may be seen as a drawback, it’s worth noting that some producers in hot countries have humidity and temperature-regulated warehouses to slow down the process, too!
As the alcohol evaporates faster than the water, the rum distillate’s alcohol concentration decreases. Producers will often control and consolidate their stock the process by transferring the contents of the same batch to fewer barrels.
Rums may be aged for as few as two years and up to several decades. Needless to say, older rum becomes exponentially more expensive as you end up with far less distilled liquid than when you started ageing it.
How Rum Is Blended
After it has been sufficiently aged, rum will almost always be blended to some degree before it is hydrated to the desired ABV and bottled. Producers will combine rum of different ages, distillation processes, batches, and even casks to produce the desired character and flavour.
As mentioned earlier, some producers simultaneously use column and pot distillation. It is only at this stage that the rums are blended together. Some producers limit blending and may offer single-cask expressions. Meanwhile, others use rum that has been aged in different casks for the same period of time.
However, the blending process can be particularly elaborate, especially given that there are no definitive regulations that dictate standards.
Indeed, blending rum is a somewhat precarious issue. For instance, unlike cognac, there are no limits on the amount of sugar or boise, a boiled wood syrup, that can be added to a blend.
Flor de Caña is known for its natural rums without additives.
Some rum brands may even add flavourings like vanilla or even molasses to alter the taste and make it feel more complex. Caramel is also often used to make the rum look older.
Similarly, it is expected that an age statement will indicate the youngest spirit in a blend as is the case with Scotch whisky. However, some feature the oldest rum or even just an estimated average age!
High-quality premium rum makers will follow tradition and strive to offer an authentic experience. However, there are few certifications to distinguish them from the less scrupulous producers.
The best approach is to research a brand and learn about its rum production. High-quality premium rum brands are proudly transparent and share as much as possible about their processes.
Meanwhile, those who conceal their practices behind “proprietary techniques” may have something to hide.
Now that you have learned how rum is made, check out some of our related resources: