Definition and production
Whether it’s called rum (for English rum), rhum (French) or ron (Spanish), this eau de vie made from sugar cane remains the common denominator between the Caribbean islands and the South American countries, with each boasting its own distinctive culture and set of traditions.
Produced all over the world, rum is a sugar cane alcohol obtained by alcoholic fermentation and then distillation, either of molasses or syrups resulting from the production of cane sugar, or directly from sugar cane juice. While rum is not strictly regulated, some countries (including France) have created regulations aimed at protecting their rum production.
Step 1 – Sugar cane juice or molasses
As a general rule, rum can be divided into those produced by distilling sugar cane juice, and those made from molasses. Obtained by crushing sugar cane, sugar cane juice deteriorates very quickly, and so needs to be fermented as soon as possible, and then distilled to produce agricultural rum. A thick, residual syrup that results from the refinement of cane sugar, molasses are used as an ingredient in desserts and sweets, and in the production of numerous types of rum.
Sugar cane (‘Saccharum officinarum ’) grows in tropical regions in the equatorial zone. It can be found in Florida, Texas, Louisiana, the West Indies, in Hawaii, in Central and South America, and also in Indonesia, Thailand, the Philippines, China, India, islands in the Indian Ocean, Australia, and in southern Spain. There are many varieties with various degrees of resistance to disease and levels of sugar content. The cane consists of water, fibres and saccharose. The saccharose is concentrated at the base of the cane.
The canes are harvested manually or mechanically at the age of 11 months, before they flower. The leaves and tops of the sugar canes are left in the fields. The bases are quickly transported to the sugar refinery to avoid any of the sugar being lost. The bases of the canes are then ground into fibres and hot water is added to extract the sweet juice. The pressing process results in two products: cane juice for the production of rum, and the bagasse, consisting of the fibrous residue, which is used as fuel.
In the case of molasses-based rum, the sugar is extracted from the cane juice and then transformed into molasses.
Step 2 – Cane wine and fermentation
Yeast is then added to the mash (molasses diluted with water or sugar cane juice), which is then fermented and gradually converted into alcohol until it eventually produces a sugar cane wine containing around 8% to 10% alcohol. A fundamental stage in the development of the flavours of the future rum, the fermentation of the sugar cane wine is conducted in various ways in different parts of the world, resulting in a very broad aromatic range.
There are three types of fermentation:
- Spontaneous fermentation
This relies on the yeasts and micro-organisms naturally present in the atmosphere or in the sugar cane juice. Such fermentation takes place in open vats and takes between 1 and 2 weeks. Small distilleries, especially those in Haiti, still practise spontaneous fermentation.
- Controlled fermentation (batch)
Usually carried out in batches, this kind of fermentation uses laboratory-grown yeasts that are added to the sweet liquid. Some distilleries cultivate and maintain their own strains of yeast that they protect, like a trademark. Such fermentation is spread over 2 to 3 days and enables the production of a consistent percentage of alcohol and range of flavours.
- Controlled fermentation (continuous)
This is a growing trend in the rum industry. It involves keeping a fermentation vat permanently filled, with the continuous addition of more molasses. This enables the yeasts to be kept active by removing a quantity of the mash, whose sugars have already been digested by the yeasts, from different sections of the vat.
Step 3 – Choice of still
Like many other spirits, rum can be distilled in a column still, continuously, or in a pot still (used by the more traditional producers). The type of distillation practised is often influenced by the country’s colonial history. Former British and French colonies still use copper pot stills, while those of Spanish origin tend to prefer column stills. The type of rum produced very much depends on the distillation method: in basic terms, heavier rums tend to come from pot stills (due to the middle cut of the distillate being collected at between 68% and 70% alcohol) while lighter rums are produced by column stills (the distillate collected has an alcohol content above 90%, thereby eliminating the heavier vapour).
Pot still - batch distillation: this ‘batch’ distillation technique requires regular stopping of the still so that it can be cleaned and allowed to rest before loading with another batch for distillation. This is the most traditional of distillation methods.
Column still - continuous distillation: usually consisting of two or four columns, each one feeding the next, this type of distillation does not require any interruption, with the columns being continuously supplied. Consisting of different levels of concentration, through which the steam circulates, this technique enables the rum’s aromatic profile to be monitored and controlled. Only its lightest vapour in terms of flavour reaches the column’s final level. The heavier vapour remains at the lower levels.
Step 4 – Ageing
Since there are no legal regulations, the ageing process and associated designations vary from one producer to another. While most ageing takes place in old bourbon barrels, rum can also be aged in cognac barrels and new oak barrels. Special cask-finished rums are quite rare; these are usually produced by Italian and French merchants, who use Banyuls, port, sherry and madeira barrels to impart flavour to the rum. There is no required minimum period, but few rums claim to be aged for more than 8 or 12 years. Matured at the site of production, the barrels are exposed to extreme weather conditions, resulting in considerable evaporation.
The evaporation issue: ageing conditions in the Caribbean, in a tropical climate, are completely different to those in Europe. As oak is permeable to alcohol molecules, which are themselves soluble in water, the combination of a high temperature and high humidity results in substantial evaporation and a faster ageing process.
In a tropical climate, a typical annual loss would be 6% to 8% of the barrel, compared to 2% in a temperate climate, such as in Scotland or Ireland.
On this basis, only 65% of the barrel’s initial contents will remain after 5 years of ageing, about 45% after 10 years, and 30% after 15 years. In Scotland it would take 55 years for a similar degree of evaporation to occur.
In addition to the increased evaporation, the ageing process itself is accelerated in tropical climates. Two years of ageing in the Caribbean is equivalent to 6 to 8 years in Scotland.
Several solutions have been considered to reduce the evaporation problem, without having to change the product description, in particular transporting the barrels of rum to Europe for ageing. There are two opposing camps: those who believe that rum should be aged in its country of origin, and those who want to age it in Europe, in order to benefit from a slower esterification and oxidation process.