We tend to think of bourbon as “America’s spirit,” but rum could have claimed the title in the country’s early days. Rum was first distilled in America in what is now Staten Island in 1664, and by the American Revolution, New England distilleries produced over 4 million gallons annually.
But while American whiskey’s trajectory has mostly risen since the westward expansion of the 1800s, rum has had a tougher go of things during the past century. By the 1960s, rum making in the continental U.S. was a moribund industry, although Puerto Rico had become a major player on the world stage. Fortunately, the craft distilling era has brought renewed attention to creating an American spin on the world’s most diverse spirit category.
While it may surprise many, sugarcane is a major American crop. Louisiana alone made 100 million gallons of molasses in 2023. So it’s no surprise that numerous rum-focused American distilleries have launched over the last 15 years, some of which now have European distribution. While bourbon enjoys the hearts and minds of many American distillers, for those looking for a wide-open field to innovate and differentiate, rum has much to offer.
Most of today’s craft distillers who make rum do it as a sideline to other spirits they consider their core focus, such as whiskey. Rum making requires fewer steps than whiskey, so it can fit neatly in between other production runs. However, as I frequently say, “It’s not hard to make rum, but it’s really hard to make a good rum that stands out.” Making a rum that goes head-to-head with the best Caribbean distilleries requires a singular focus on the spirit. And a growing number of American rum distillers have made a long, sustained investment to do just that.
Defining Ground Rules
The U.S. Code of Federal Regulations defines a Standard of Identity for different classes of distilled spirits, including bourbon and rum. Whiskey’s Standard of Identity states:
Spirits distilled from a fermented mash of grain at less than 95% alcohol by volume (190 proof) having the taste, aroma and characteristics generally attributed to whisky and bottled at not less than 40% alcohol by volume (80 proof)
Rum’s standard of identity is essentially the same, except “fermented mash of grain” is replaced by “fermented juice of sugar cane, sugar cane syrup, sugar cane molasses or other sugarcane by-products.”
Bourbon is a subtype of whiskey, whose definition reads:
Whisky produced in the U.S. at not exceeding 80% alcohol by volume (160 proof) from a fermented mash of not less than 51 percent corn and stored at not more than 62.5% alcohol by volume (125 proof) in charred new oak containers.
The TTB’s whiskey class has other subtypes, including rye, Scotch whisky, and Irish whisky; The TTB recognizes each subtype as a distinct spirit. The same holds true for the TTB’s brandy class, which includes subtypes such as Cognac, Calvados, and pisco. But when it comes to rum, there are no subtypes; a cane juice rum can’t even be differentiated from a molasses rum. It’s a silent indicator that U.S. regulations pay less attention to rum than whiskey or brandy — even though it’s just as diverse.
Base Materials
When distilling from grain, all the fermentable sugar resulting from mashing goes towards making whiskey and nothing else. In contrast, a single batch of cane juice can be turned into rum, sugar crystals, and molasses; and in different ratios depending on production choices. Historically, sugar crystals are more profitable than rum, which is why most rum is made from the residual sugar remaining after sugar crystals production.
Whiskey making requires an additional step relative to rum. While sugarcane sources merely need dilution to the correct Brix level to start fermentation, whiskey makers must first cook their grains to convert the starch into fermentable sugar. Whiskey distillers must also dispose of the mash solids.
Just like different types of grain require different mashing approaches, rum distillers must tailor their fermentation protocols to the specific type of sugarcane material, of which there are four:
- Cane juice
- Molasses
- Cane syrup
- Raw sugar crystals
Theoretically, fermenting cane juice is the simplest as it’s conceptually just a matter of adding yeast. The typical Brix of cane juice is near ideal for fermentation, and there are few undesirable compounds in properly milled and filtered juice. However, cane juice spoils within hours after milling, so distillation must be within a short distance of the cane fields and mill. This effectively limits cane juice usage in the U.S. to the American South, Hawaii, Puerto Rico, and the U.S. Virgin Islands. Cane juice distilleries either need their own mill or must partner with a nearby mill to acquire juice immediately after milling. For example, Louisiana’s Oxbow Rum uses cane juice from its family-owned Alma Sugarcane Mill.
One step away from sugarcane juice is cane syrup, which is concentrated cane juice made by heating it until most of the water evaporates but before sucrose crystals form. Due to its high sugar content, cane syrup won’t spontaneously start fermenting, doesn’t need special handling, and can be stored in large tanks for considerable periods.
However, as noted earlier, most rum is made from molasses. Only in recent years are the economics reversing in certain cases. The key difference between molasses and cane syrup production is that with molasses, the heating continues until sucrose crystals form. After filtering those crystals out, molasses is the thick, dark liquid that remains. It contains various forms of sugar and non-sugar compounds like ash.
Molasses is sold in different grades. The USDA defines four: A (“fancy”), B (“choice”), C (“standard”), and Substandard. Lower grades contain less fermentable sugar and higher levels of non-sugar compounds, which can hinder fermentation. The lowest grade molasses, aka blackstrap, may have insufficient sugar content to sustain fermentation. If so, cane syrup or raw sugar crystals can be added to increase the Brix.
The use of raw sugar crystals is allowed by U.S. law but is viewed by some as inauthentic to rum’s tradition of being made from molasses, or less frequently, cane juice. If you were to create two mashes, one from molasses and the other from raw sugar crystals, the ratios of sucrose, glucose, fructose, and non-fermentable solids would differ. Since these ratios influence the resulting congeners from fermentation, the end result will be different rums.
As you’d expect, a mash using cane syrup, molasses, or raw crystals must be diluted to bring the Brix to a level roughly equivalent to that of cane juice.
Fermentation
While bourbon derives most of its flavor from aging, rum comprises both aging-forward styles similar to bourbon as well as styles where most of the flavor in the finished rum is created during fermentation. Many rums have substantially more flavor than bourbon without going anywhere near a barrel. We can call these rums fermentation-forward. Such rums bypass the usual three-day fermentation with Saccharomyces cerevisiae, opting instead for a much longer fermentation using exotic yeasts like Schizosaccharomyces pombe. The resulting wash has far more congeners than either a bourbon or a light rum wash like Bacardi and similar brands use.
A point in common between sour mash bourbon and many fermentation-forward rums is the inclusion of spent wash in subsequent fermentations. (Spent wash is alternatively referred to as backset, stillage, vinasse, or, in Jamaica, dunder.) The acid in the spent wash creates a more conducive environment for creating esters and other flavor congeners. A handful of American rum makers, including Louisiana’s Roulaison, use both spent wash and more exotic yeast strains.
Distillation
Distillation is where bourbon and rum share much in common. Both batch and continuous distillation are used, with larger bourbon and rum producers favoring column stills for their high output. But when it comes to column stills, some rum makers undeservedly get a bad rap for using them. Rum can indeed be column distilled to near neutrality at 190 proof, but many rum makers column distill to 160 proof or less, creating a very flavorful distillate. For example, Martinique rhum agricole is continuously distilled to 150 proof or less, and no one says it lacks strong flavor.
For batch distillation, most medium- to large-sized Caribbean distillers use a type of still that whiskey makers rarely use. The double retort pot still consists of a regular pot still connected in series to two tanks (“retorts”) that function as additional distillation chambers, creating three distillations per batch. The pot’s hot vapor travels through the lyne arm into liquid within the first retort, causing the liquid to boil. Those vapors pass via a pipe connecting the first to the second retort, where the process repeats before condensing. In bourbon parlance, each retort is equivalent to a thumper connected to a column still.
Aging
Bourbon’s aging requirements in the U.S. are far stricter than rum. Not only must bourbon be aged, but the aging must be in new oak containers with entry proof at 125 proof or less. In contrast, rum can be either unaged or aged, and aging can happen in less-costly used whiskey barrels. There are no constraints on entry proof for rum, but as a point of reference, most Caribbean distillers age in ex-bourbon barrels with an entry strength between 120 and 140 proof.
Bourbon’s distinctive vanilla and oak lactone flavors are extracted from the cask’s wooden walls, which are chock-full of flavor compounds. Since rum is usually aged in ex-bourbon casks, those strong bourbon-y notes are mostly missing. However, a few distillers like Massachusetts’s Privateer and Georgia’s Richland also use new American oak barrels. The finished rums have a flavor profile familiar to bourbon enthusiasts.
Regarding age statements and rums from different regions, age is truly just a number. Due to the Caribbean’s higher average temperatures, aging occurs around twice as fast there as in Kentucky, for instance. Thus, a rum aged for five years in Barbados is roughly equivalent to the same rum aged for 10 years in Kentucky.
The TTB allows the bottled-in-bond designation for rum, and several producers have bottled-in-bond expressions.
There’s a common misconception that “white rum” is unaged. In fact, the vast majority of mainstream white rum on store shelves is aged for a year or more before it’s carbon filtered to remove color. Puerto Rico, home to Bacardi and Don Q, requires all rum to be aged for at least one year. The tequila equivalent of an aged and filtered white rum is “cristalino.”
Additives
In the final stages before bottling, the major distinction between bourbon and rum in the U.S. is that bourbon doesn’t allow additives other than caramel coloring. For rum, the regulations allow up to 2.5% per volume of “blending materials,” which in practice are typically sweeteners and extracts.
Regulations
Regulatory differences between regions can be troublesome for producers. If you plan to export your rum, know that the rest of the world isn’t always in sync with U.S. rules.
The E.U. has a broader allowance for alcoholic strengths. A bottled rum sold in the E.U. can be as low as 37.5% ABV versus 40% in the U.S. The E.U. allows distillation up to 96% ABV, whereas the U.S. caps it as 95%. E.U. regulations also prohibit using crystalized sugar as a base material.
Agricole, the French word for agricultural, is a protected term in the European Union. It can only be used for rums made in Madeira and the French overseas territories, e.g., Martinique. Thus, U.S.-made “agricole” rums like Hawaii’s Kuleana can’t be sold in the E.U. if their label says “agricole.”
Certain countries, including Australia, require a minimum aging period to be sold as rum. However, by replacing rum on the label with something like “cane spirit,” they usually can be sold at a younger age.
Additional Reading
The above is just the briefest introduction to the technical side of rum making. For those looking for more details, there are a good number of books and technical publications that delve much deeper. For example, the writings of Raphael Arroyo in Puerto Rico from the 1940s are virtually unknown today, but are a gold mine of scientific research and analysis focused entirely on rum. Stephen Shellenberger at the Boston Apothecary website writes in very deep detail about rum fermentation. And finally for those looking for deep information about what Caribbean distilleries are doing today, my book Modern Caribbean Rum contains production details for over 70 distilleries.
