An important part of rum production for the more serious rum lovers, is how long rum has been aged. It is one of the more interesting aspects of producing rum, and also the least known aspect. Since there are no actual consistent laws regarding the aging of rum around the world, it is aged for various amounts of time and in different locations. You can find it aging high up in the mountains, underwater, or at sea level. This means that there are many different flavors and styles of rum. It may be bottled without aging at all, or aged in an oak aging barrel for any length of time up to thirty years or more. It is aged in such extreme locales as the tropic region of the Caribbean and the mountains in Nepal.
A fairly constant quality of aging rum, is the art of maturing it in a once used bourbon oak aging barrel. It is one of the more accepted methods of aging for rum producers these days. This makes for a wonderful tasting rum.
You may wonder why rum is aged in used bourbon barrels. The answer to this question is fairly simple. A law that was enacted in 1964 by Congress deemed Bourbon Whiskey to be a “distinctive product of the United States”. A law that was contained in the act said that Bourbon had to be aged in a charred oak aging barrel that is new.
Due to this law, bourbon producers ended up with a surplus of used oak barrels. There were some which were only used for a minimum of two years that was required by law in order to qualify it as American Bourbon. Distillers of rum from around the world were happy to take on as many of the barrels as they possibly could. This way, the bourbon distillers were helping out the rum distillers, and it kept down the cost of aging their whiskey. Small rum producers received the oak aging barrel in one piece, and had to conduct a curing process to ensure that they were not dried out during transport. Larger producers received the barrels as bundles, so they had their coopers re-char and rebuild them.
The aging process for bourbon involves new white oak barrels. Therefore, whiskey extracts more color and flavor from the barrel during the first use of it. Caramel and vanilla are the most common flavors which are extracted. The caramel is produced from the oak charring.
A barrel is made by cutting American Oak into stave, and then heating it and bending it into an ovular form. It is then toasted in a small fire for around twelve minutes, so that the sugar from the wood is caramelized. Then, it is put on a larger fire for only around six to twelve seconds, so that the inside is burned and creates a charcoal layer. A consistent flavor in whiskey is possible if the inside of the barrel is charred evenly.
When slow aging occurs, whiskey is said to breathe in the barrel. Fluctuations in temperature cause whiskey to contract and expand out and in of the oak aging barrel. It is mellowed through this process, which is what gives it an appearance and flavor that is distinct. This maturation occurs quicker in the Bourbon belt that in the more damp and cool climates of Ireland and Scotland. Whiskey will move 3/4 of an inch in and out of the white oak, so it will draw out wood flavors that are so well known in bourbon.
When whiskey ages in an oak aging barrel for many years, it results in there being traces of bourbon being left behind in the wood. Many of the aged rums that you will find today contain hints of bourbon, depending on how old the oak aging barrel is in which it was aged. Some rum producers will re-char barrels in order to give more flavor and color to the rum. An additional trick that rum producers use is adding in pieces of discarded oak barrels or wood chips to aging rum. This leads to even more flavor and color being imparted to the rum.
Size matters when it comes to an oak aging barrel, as well. The smaller the oak aging barrel is, the more contact the rum will have with it. If you are using a larger oak aging barrel, there will be less contact between the rum and the oak. A standard oak aging barrel size is about 195 litres. This is used by the majority of rum producers. Some of the producers use small barrels to have a quick tranfer of flavor, or larger ones if they want to age it for a longer period of time. Producers in the French islands favour using these large vats.
Different types of oak produce different flavors. American oak has a rather strong aroma, while French oak has more of a subtle flavor. When rum is distilled, it is colorless and has a taste that is very raw and pungent. Depending on the length of time it is aged, the color will vary, with it appearing darker the longer it ages. However, there are white rums that are aged for a long while. They are filtered through carbon to take out the color, but the flavor is left in it. Many of these are not priced as high as the darker ones, so they are aged for a short time.
Rum will slowly evaporate if it is aged for a long time in an oak aging barrel. It is typically called the angel’s share. The rate of evaporation can be up to 10% a year in the Caribbean, but it may be as little as 2% in the colder regions. While an oak aging barrel allows rum to breathe, evaporation itself caused a distiller to lose a large amount of money in lost profits. The longer you age rum, the more evaporation happens and there is less rum to bottle. Distillers must determine the point of no return when it comes to their profits. If the local law permits, the distiller can top the oak aging barrel off with a rum of similar age, from the same batch.