Unlike some other spirits, such as Cognac and Scotch, rum has no defined production methods. Instead, rum production is based on traditional styles that vary between locations and distillers.
Most rum produced is made from molasses. Within the Caribbean, much of this molasses is from Brazil. A notable exception is the French-speaking islands where sugar cane juice is the preferred base ingredient.
Yeast and water are added to the base ingredient to start the fermentation process. While some rum producers allow wild yeast to perform the fermentation, most use specific strains of yeast to help provide a consistent taste and predictable fermentation time. Dunder, the yeast-rich foam from previous fermentations, is the traditional yeast source in Jamaica.
“The yeast employed will determine the final taste and aroma profile,” says Jamaican master blender Joy Spence. Distillers that make lighter rums, such as Bacardi, prefer to use faster-working yeasts. Use of slower-working yeasts causes more esters to accumulate during fermentation, allowing for a fuller-tasting rum.
As with all other aspects of rum production, there is no standard method used for distillation. While some producers work in batches using pot stills, most rum production is done using column still distillation. Pot still output contains more congeners than the output from column stills and thus produces a fuller-tasting rum.
Many countries require that rum be aged for at least one year. This ageing is commonly performed in used bourbon casks, but may also be performed in stainless steel tanks or other types of wooden casks. The ageing process determines the colouring of the Rum. Rum that is aged in oak casks becomes dark, whereas Rum that is aged in stainless steel tanks remains virtually colourless. Due to the tropical climate common to most rum-producing areas, rum matures at a much faster rate than is typical for Scotch or Cognac. An indication of this faster rate is the angels’ share, or amount of product lost to evaporation.
While products aged in France or Scotland see about 2% loss each year, rum producers may see as much as 10%. After ageing, rum is normally blended to ensure a consistent flavour. Blending is the final step in the Rum making process. As part of this blending process, light rums may be filtered to remove any colour gained during ageing. For darker rums, caramel may be added to the rum to adjust the color of the final product.