Rum Aging

Inside a well used charred American oak barrel.

Rum Aging
One of the most important aspects of rum production for most serious rum lovers is the length of time each rum is aged for. This is probably one of the most interesting aspects of rum production and the one that least is known about.
As there are no consistent laws on how rum is aged throughout the world, rum is aged in various locations and for varying lengths of time. Rum can be found aging at sea level, thousands of feet up in the mountains and even underwater, thus creating wide varieties in styles and flavours. Rum can be bottled straight from the still with little or no aging, or can be aged up to thirty years or more in oak barrels. Rum is aged in the humid tropical islands of the Caribbean, in the cold climates of Northern Europe and even in the mountains of Nepal.
However, one pretty constant aspect of rum aging is the widely accepted art of maturing the rum in once used bourbon oak barrels. This is the accepted method of aging for the vast majority of rum producers today.
You may ask why is it that rum is aged in used bourbon barrels. There is a fairly simple answer to this question. By a law enacted in 1964, the United States Congress recognized Bourbon Whiskey as a "distinctive product of the United States." One of the laws included in this act was that; "Bourbon must be aged in new, charred oak aging barrels."
As a result of this law bourbon producers found themselves with a glut of used oak barrels. Some of them had only been used for the minimum two years required by law to qualify the distilled spirit as American Bourbon. Rum distillers all over the world were only too glad to acquire as many of these barrels as they could get their hands on. Not only would the bourbon distillers be helping the rum distillers, it was also a way of keeping their own costs of aging their whiskey down.
The larger rum producers will receive their oak barrels broken down into bundles and have their team of coopers rebuild and re-char the barrels. The smaller companies will recieve their barrels in one piece and begin using them usually after a short curing process to ensure the barrels have not dried out during transport.

Old Barrel Staves show how Rum has penetrated the Oak.
Charring the inside of oak barrels at Zacapa.

Bourbon is aged in new white oak barrels. This means that the whiskey extracts the most colour and flavour out of the barrel in its first use. The predominant flavours extracted from the barrel are vanilla and caramel. The caramel flavour is produced mainly from the charring of the oak (shown right).
To make a barrel the American Oak is cut into staves which are super heated and bent into ovular form. The barrel is then "toasted" by sending it through a small fire for about twelve minutes to caramelize the sugar in the wood. Next it is applied to a larger fire for six to twelve seconds to burn out the inside and produce a charcoal layer. The charring has to cover the inside of the barrel evenly so as to provide a consistent flavour to the whiskey.
During the years of slow aging the whiskey is believed to "breathe" in the barrel. With fluctuations of temperature the whiskey expands and contracts in and out of the oak barrel. This expansion and contraction of the whiskey through the caramelized layer of charred wood inside the barrel mellows it, giving it the distinctive flavour and appearance. This maturation of the whiskey happens quicker in the Bourbon belt than it does in the cool, damp climates of Scotland and Ireland. The whiskey moves about 3/4 of an inch in and out of the one inch thick white oak, thus drawing out all the wood flavours predominant in bourbon.

Charring the inside of an oak barrel.

The result of the whiskey aging for many years in the oak barrels are that it draws many of the original flavours from the wood, but can leave behind traces of the bourbon. In many of todays aged rums you will be able to taste slight hints of bourbon, some more than others, depending on how old the barrel it was aged in was. Rum producers often re-char their barrels so that they impart more colour and flavour to the rum.(shown above at Zacapa) Another trick many rum producers use is to add wood chips or pieces of discarded oak barrels into the aging rum. This provides more oak contact for the rum to draw more colour and flavour.

Obviously size does matter aswell. The smaller the barrell, the more contact the rum will have with the oak. The larger the barrell, the less contact with the oak. Most rum producers use a standard size barrel, around 195 litres. Others use smaller barrels for a quicker flavour transfer or huge oak vats which generally take longer to age their rums. These larger vats tend to be favoured more by the French islands, eg. Barbancourt.(shown below)

There are also differences in the types of oak used to make the barrel. French oak gives off subtle flavours whereas its American counterpart gives off much stronger aromas.

All rum when it is distilled is clear or colourless and tastes pungent and raw. The longer the rum is aged in the barrel the darker the rum will become. Many white rums these days are aged for extended periods of time and then filtered through carbon to remove any colour gained during the aging process, but leaving behind all the added flavours. Most white rums do not sell for as much as their darker cousins and so the aging length is often pretty short.

For the darker rums caramel is often added to the final blend of rum to give it a consistent colour. This will often have an influence on the final falvour of the rum and can be tasted in many dark rums.

French Limousin Oak Vats at Barbancourt, Haiti.
Many thanks to Seamus at http://bunnyhugs.org/ for this photo.

The Angel's Share

When rum is aged for long periods of time in an oak barrel it will slowly evaporate. This evaporation is often called the angel's share. The evaporation rate can be as high as 10% a year in the tropical Caribbean, while it can be as little as 2% for Cognac or whisky producers in colder climates. While the oak barrel allows the rum to breath through the wood during the aging process, which in turn adds great flavour to the rum, this evaporation is costing the distiller large ammounts of money in lost profit. Obviously the longer you age the rum, the more is lost to evaporation and so less rum is left to bottle. A distiller often has to decide what is the point of no return in regards to profit. Where local laws permit, distillers can top up their barrels with a rum of similar age or from the same batch.

A Solera System at Oliver & Oliver, Dom.Rep.
Oliver and Oliver buy aged rum and then further age it using the Solera method.

Solera Aging
An innovative way of aging rum that is most often employed by rum producers in Spanish speaking countries is called the Solera method of aging. Solera was once described by a rum expert as "Spanish for cheating", but infact is just a way of taking the raw edges off aged rum much quicker than the traditional one barrel methods of aging and gives the master blender much more control over the final product.
Solera is a process for aging liquids such as wine, sherry, madeira, vinegar, brandy and of course rum. It is a method of fractional blending in such a way that the finished product is a mixture of ages, with the average age gradually increasing as the process continues over many years.
Rum produced from a solera system should not have a formal age statement as it is a blend of rum from many vintages, but for marketing purposes the label will often display some sort of age.
The only drawback from this system of aging is the initial investment in barrels, rum and warehouse space.
The Solera system consists of a stock of rum in oak barrels, split into graduated units each of different maturation ages and each of equal volume. The final stage of finished rum is called the Solera. The supporting steps or scales are called criaderas. Rum for bottling and blending is drawn from the Solera, which is replaced by rum from the immediately supporting criadera of rum of the same style, but a little younger and less complex. From there, replacements proceed in succession down the scales of the system until the youngest criadera is refreshed with carefully selected young rum. The number of criaderas used before the solera varies from distillery to distillery. Many distillers will finish their rum in barrels previously used for sherry or port, adding even more flavour to the finished product.
When rum from the oldest barrels of any one Solera is withdrawn for bottling, usually between 10 to 15% of the rum in the barrel, the same amount of rum is removed from an equivalent number of barrels of the first cridera or nursery. The rum is then blended and added in equal proportions to the space left in the barrels of the Solera. During the following months or years the slightly younger rum will take on the characteristics of the majority of the older rum in the barrel. All the rum in the barrel becomes exactly the same as the rum which was taken out months previously. 

Filling new barrels in a Solera at Oliver & Oliver
Inside a non-charred and a charred barrel.
This barrel display is at the Don Q Museum in Old San Juan, Puerto Rico.
Sealing an old barrel at Ron Barcelo.
Dried palm leaves are used to seal old barrels.
A stack of palm leaves at Ron Barcelo.
Palm leaves are often used to seal rum barrels.
Wood chips inside a charred barrel.
Wood chips are often used to give the rum more contact with oak.
Cooper's workshop at Ron Barcelo.
Barrel Parts.