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 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 yeasts 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. Distillers who 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, no standard method is 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, so produces fuller-tasting rums.
Aging and blending
Many countries require rum to be aged for at least one year. This aging is commonly performed in used bourbon casks, but may also be performed in other types of wooden casks or stainless steel tanks. The aging process determines the color of the rum. When aged in oak casks, it becomes dark, whereas rum aged in stainless steel tanks remains virtually colorless.
Due to the tropical climate common to most rum-producing areas, rum matures at a much higher rate than is typical for whisky or brandy. An indication of this higher 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, tropical rum producers may see as much as 10%.
After aging, rum is normally blended to ensure a consistent flavor. Blending is the final step in the rum-making process. As part of this blending process, light rums may be filtered to remove any color gained during aging. For darker rums, caramel may be added to adjust the color of the final product.