FERMENTATION: 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 sugarcane 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.