In the seventeenth century, Robert Lignon described the clear spirit he found on the island of Barbados as ". . . a hot and vile liquor." A few years later, the captain of a Dutch ship returned from the West Indies and wrote in his log, ". . . the spirits are now smoother to the tongue and have acquired a golden color during the voyage." In the next century, George Washington ordered a hogshead of the finest aged Barbados rum for his inauguration party.
Unlike other distilled drinks such as vodka, whisky, gin, or even brandy, rum varies from a clear, colorless spirit through hues of gold and brown to black but there's a lot more to the color of the spirit in your glass than meets the eye. From their transparent infancy, rums change as a result of aging, the addition of caramel or coloring, filtration, and that mysterious quotient of magic present in every bottle.
Some Caribbean spirits are bottled directly from the still, but most distillers age a portion of their rum in oak barrels that were previously used to age whisky or bourbon in the U.S. or Canada. A small number of rum barrels come from Europe where they aged Scotch whisky, Cognac or, in a few cases, sherry. Before these barrels were filled with other spirits, the inside surface of the barrel staves were charred. Some rum distillers scrape the original char from the barrels and then fill them with rum to be aged. Others rechar the barrels, while a few distilleries simply refill the once-used barrels with their rum. In a handful of cases, new barrels are charred over a wood fire to avoid contamination from the hydrocarbon residue of a gas fire.
The chemistry of aging isn't fully understood, but it's universally accepted that aging mellows and improves the taste of freshly distilled spirits. While the rums are sleeping in oak barrels, natural tannins in the wood impart a golden tint that yields to a rich brown cast after several years. The alcohol in the rum acts as a solvent and attracts the tannins in the porous wood as well as esters which will give rum, or any other spirit, a slight vanilla flavor as well as a smoky oak tone depending on the age of the spirit.
Most rum producers age their rum at 70% to 80% alcohol. A few dilute their spirits to nearly bottle-strength, 40 to 45% alcohol by volume, before putting the barrels away for aging. A lower alcohol content during aging tends to leech slightly lighter esters and phenols from the wooden barrels while a higher alcohol content will attract heavier compounds and associated flavors. Most distilleries age their rum at a higher strength as this requires fewer barrels, but a higher alcohol content also contributes to higher evaporation losses, known as the angel's share.
Before the aged spirits are bottled, pure water is blended into the rum to reduce the alcohol content. Diluting the aged rum, however, also dilutes the color of the matured spirit. In most cases the rum is not as pleasing to the eye as the distiller would like, so caramel (burnt sugar) is added to adjust the color. Because not all barrels tint their contents to the same cast, caramel is sometimes sparingly added so that all rum bottled under a particular label will be the same color. In other instances, generous amounts of caramel are used to make the spirit black, as in the case of Myers's from Jamaica or Gosling's from Bermuda.
Just as some wines are fermented to be drunk within a few years (or even months) of bottling, some rums are distilled to be consumed as soon as they are bottled. In the case of French rhum agricole, the raw spirits are allowed to rest for a few months in large vats while the light gases formed during fermentation are released. On the other islands, unaged over-proof rums are bottled straight from the still for their very loyal local market. In both cases, these rums would lose much of their character, appeal, and consumer base if they were aged.
Distillers typically blend their aged rums from a variety of barrels containing rum of different ages and characters. Variations in the aged spirit are influenced not only by the barrel but also by where the barrel was stored in the warehouse. Samples from each barrel are tasted, and then the contents of those barrels are blended to meet the taste profile that the master blender wants to bottle. This final blending takes place over a few days while the intricate flavors of the different rums in the blend marry. In a few cases, the blender will recask the rum and then allow the blend to mature in another barrel in a process called "second maturation." The term "single barrel" is sometimes used to designate these special rums, but these are rarely bottled from a single barrel, as they are in the bourbon industry. In rare cases, sherry casks are used to mature the rum in the final phases of aging before they are bottled as the best offerings from the distillery.
Moreover, some distillers top off their barrels annually from rum of the same age, while a few have adopted various forms of the Solera process from the Spanish wine industry. In the Solera process, the barrels are topped off each year with rum that is one year younger than the barrel to be refilled. At the end of the Solera process the spirit is bottled.
Age statements are beginning to appear on rum bottles, something that has caused quite a stir in an industry where such details have historically been left up to the distiller or blender. If a spirit is imported to the U.S. and there is an age statement, the age must reflect the age of the youngest spirit in the bottle. Look for an actual age statement and not just a number. Some distillers use the word "premium" to describe their best aged spirits. Another common description is the word "anejo," which simply means "old" in Spanish. "Gran anejo" denotes something even older. Neither of these terms really tells you how long the rum has aged, but like the word premium, they are generally reserved for the better rums.
The French Caribbean distillers label their rhum "vieux" if it has aged at least three years. Other designations such as "tres vieux" denote much older rums and "hors d' age" applies to a blend of old rums. Vintage years are not uncommon, but it is important to determine when the rhum was actually put in the bottle and not just when it was distilled, as the aging process of any distilled spirit ceases upon bottling.
Age matters in a lot of things, but don't get hung up on the age of your rum. Much more important than age is maturity. If you're used to drinking scotch or whiskey, you probably think spirits have to be at least 12 to 15 years to be of premium quality. I wouldn't argue that many lesser spirits need to be aged a long time, but the truth of the matter is that many very good rums are aged only a fraction of that time. Because sugarcane spirits intrinsically don't contain as many offensive congeners as other spirits, they tend to mature faster. It's generally agreed that the warm Caribbean climate helps spirits aged there to gently reach maturity faster than spirits aged at higher latitudes. This isn't to say that rum isn't any good after spending 12 or 15 years sleeping in an oak barrel on a tropical island, but unlike spirits distilled from grain, rum doesn't need to be as old to be quite palatable. In fact, some of the oldest rums have passed their pinnacle of maturity and been over-powered with the smoky oak and burnt tobacco flavors associated with decades in a charred barrel.