Climate change
Ian explores how climate affects the rate of maturation
When meeting someone new an initial impression is based on appearance, talking provides additional information, and a more comprehensive verdict can follow. Similarly, a bottle of rum is judged initially on appearance: by the shape of the bottle and design of the label, the graphics and typography, which also provide more information. One supposed insight into a rum is a number that confirms its age.
The choice spans a few generations, including Bacardi Anejo Cuatro 4-years-old and Reserva Ocho 8-years-old, with Appleton Estate offering a 12, 21 and even a 50-years-old. Age statements provide a way of navigating the range, and comparing rums of the same age. Comparing rums of different ages is often, however, proceeded by a belief that ’older is better.’ Older is different. The flavour profile evolves continually during the ageing process, and while younger rums offer different flavours to older rums, they can provide an equally fulfilling experience. What really matters is how a rum evolves while ageing, and the final result, rather than the total number of years.
The starting point is the freshly distilled spirit, which ranges from elegant to richer and fuller-bodied, as each distillery has its own house style, termed ‘distillery character.’ An often typical choice for ageing are barrels previously used to age Bourbon, which are renowned for adding vanilla, crème caramel and crème brûlée notes. As soon as the spirit is filled into a cask it begins to evolve: the influence of ageing increases, while the original distillery character decreases and evolves.
The rate at which this balance changes depends on various factors, and with so many of the rums we enjoy produced in the Caribbean and South America the climate is a fundamental consideration.
Peak temperatures are in July-August, reaching for example 22-32 degrees centigrade in Cuba and 24-33 degrees centigrade in Jamaica. The lowest temperatures are in January and range from 21-30 degrees centigrade in Jamaica and 1626 degrees centigrade in Cuba. Humidity in Jamaica is 80-85 per cent, and 80 per cent in Cuba. Needless to say, there can be significant variations within the Caribbean.
“Bermuda is further north of other Caribbean islands, with a sub-tropical climate that rarely drops below 60 degrees fahrenheit and maxes out at 89 degrees fahrenheit (16-32 degrees centigrade). There’s no rainy season, but an average humidity at nearly 80 per cent makes it hotter than the actual temperature in the summer; damp and cool in the winter,” says Malcolm Gosling Jr, commercial director, Goslings Rum.
The extent to which the climate influences the ageing process also depends on the type of ageing warehouse. Brick warehouses provide the greatest degree of insulation against the weather, and consequently more stable temperatures. Concrete warehouses transmit the weather more readily, and metal warehouses even more so. Meanwhile, the use of limestone is particular to Bermuda.
“Our buildings and warehouses, including the roofs, are built out of Bermuda limestone, which creates a specific environment. The walls are around one foot thick and retain the moisture which, in turn, provides good insulation and promotes stable temperatures. Open at both ends, air passes through so there is a constant influx of fresh sea air,” says Malcolm Gosling Jr.
Hotter climates ‘accelerate’ the ageing process, as the rate of reactions within a cask increases as the temperature rises. This suggests hotter climates produce the same result as cooler climates, within a shorter schedule. But that’s not the case. A change in the rate creates a different equilibrium within a cask, and a different result.
“We’ve aged our casks off the island, in different climates, and when casked at the same time as Bermuda, there was always a noticeable difference after just six months to a year. Bermuda creates a softer, complex flavour which we couldn’t achieve elsewhere,” says Malcolm Gosling Jr.
The temperature determines a significant aspect of ageing, which is the evaporation rate, and this also needs to be seen in conjunction with another key influence, oxidation. In the Caribbean the evaporation rate is six-nine per cent of the contents of the cask per annum (compared to Scotland at around two per cent) and the higher the temperature the greater the rate. Evaporation ‘concentrates’ the character of the spirit, by physically reducing the volume of liquid, but there is also a refining and mellowing effect. Going beyond such generalisations is difficult as the influence of evaporation is not fully understood.
“In general, the quickest rate of evaporation tends to create liquids that are more concentrated and drier. For example, Havana Club 15-years-old is an extremely dry rum compared to the range,” says Asbel Morales, Havana Club master of Cuban rum.
Meanwhile, as the level of liquid decreases the cask can accommodate larger amounts of air (which passes through the staves), and consequently the influence of oxidation increases. This process is renowned for refining the character, and increasing fruitiness, but is hard to get a grip of and even less understood than evaporation.
“Evaporation losses average around seven litres a year from a 200 litre cask, and as air enters the barrel, oxidation of the harsher compounds occurs,” says Malcolm Gosling Jr.
As the ageing process continues the flavour profile of a rum evolves significantly.
“Rums aged in barrels that are 10-15 years old show notes that are a mixture of ripened tropical fruits and spices, dry and robust, while also adding structure to blends. Rums aged in barrels that are 15–20 years old have notes of cocoa, dark chocolate, vanilla and light oak, while also being sturdy and strong, they add body and roundness to blends.
“Rums aged in barrels that are 60 plus years old have notes of sweet tobacco, vanilla, caramel, caramelised tropical fruits, cinnamon and other spices, and are complex and rich. These casks give soul to our more mature rums,” says Asbel Morales.
Consequently, it is perfectly justified to say ‘older is better,’ but only if this is based on preferring the flavours that an older rum delivers. Otherwise it’s just a generalisation that doesn’t stack up.