Distillation: from cane wine to rum
In the first episode of our series, we learned how sugarcane juice or molasses is fermented with yeast to make a low strength cane juice “wine” of around 8% ABV. To create rum from this wine, we must concentrate the alcohol while simultaneously removing poisonous and unpleasant tasting organic compounds.
Distillation is the process of using heat to concentrate alcohol and remove undesired compounds. In rum making, distillation separates the cane wine into desirable portions (ethanol and pleasant flavors) from undesirable portions (methanol, water, and unpleasant flavors.)
How does heat enable this separation? Each organic compound in cane wine, including ethanol and water, have their own distinct boiling (vaporization) temperature. For water, it’s 100°C; for methanol it’s 78.2°C. Upon heating the cane wine, the various compounds within vaporize at different times. Compounds with lower boiling points generally vaporize early on, while compounds with higher boiling points vaporize later.
The original and simplest type of distillation, known as batch or pot distillation, dates to the 1300s, if not earlier. A fermented liquid is placed in an enclosed kettle, then heat is applied. As the liquid warms it starts to slowly vaporize; the vapors then flow out a small “neck” attached to the kettle. The vapor then travels through a narrow tube which passes through a water-cooled chamber. The cool water condenses the vapor back into liquid, ready to be collected. Collectively, the aforementioned equipment is known as a pot still.
As noted earlier, the various organic compounds within the kettle vaporize at different times. Depending on the mix of compounds emerging from the still at any moment, the distiller either collects or discards them. Naturally, the desirable portions are what they collect.
In the 1800s, a new form of distillation was created — continuous distillations. A continuous still (also known as a column still) has one to five vertical columns. At regular intervals inside the columns are circular metal plates spanning the column’s entire width. Openings in the plates allow vapor and liquid to travel up and down through the column.
During distillation, a steady flow of steam enters at one level of the continuous still. At a higher level, the cane wine also feeds in. When the rising steam and descending cane wine meet, the steam’s heat vaporizes the cane wine. Eventually, every plate is covered in liquid, with successively higher plates holding higher alcoholic strength liquid. An opening on column’s side allows a plate’s liquid to slowly drain out for collection.
The advantage of continuous distillation is that it makes rum much faster and at greater volumes. While pot stills need to be cooled, cleaned, and refilled after each distillation, continuous stills can operate for weeks without stopping. However, pot and column distilled rum are far from identical, flavor-wise. Pot distilled rums are usually described as being “heavy” and sometimes “oily”, whereas column distilled rums are usually known for their lighter, cleaner flavor.
Certain rum making regions are known for the type of still they use. For example, Jamaica is best known for its heavy pot distilled rums, whereas Puerto Rico and Cuba are known for their light, continuous distillation rums. Martinique also uses continuous distillation primarily, but by distilling with just one column, its distilleries make a very flavorful rum.
Many distilleries use both pot and column stills and blend the rums from each to create their own unique flavor profile. Barbados rums in particular are known for pot batch and column distillates.
Regardless of how a rum is distilled, what emerges from the still is a clear liquid at high strength —usually between 70% and 95% ABV. In our next episode, we’ll learn how aging in wooden casks transforms this liquid into finished rum.