What is tropical ageing in rum?

Tropical maturation is the maturing of rum in a warm, humid climate, which makes the spirit react faster with the wood and causes more to evaporate each year than in northern Europe.

Most rum matures in the country of origin, in a warehouse without cooling. The temperature rises and falls over the course of a day, the spirit expands and contracts and is thus repeatedly pressed into the inside of the cask. The rum house E&A Scheer writes that the warm, humid conditions speed up maturation and increase the exchange between the rum and the oak. Rum that matures in Europe, for example in a warehouse in the Netherlands or Scotland, goes through that rhythm much more evenly.

Heat drives evaporation: a cask in a warehouse in Barbados or Guyana loses more content per year than the same cask in a cool Scottish warehouse.

That loss is called the angel’s share in the trade. How large it is is not fixed. It differs per warehouse, per cask, per layer in the rack and per year. In warm, humid conditions mainly the water evaporates, reports E&A Scheer, so that the alcohol percentage in the cask can actually rise instead of fall. There is no fixed percentage per year that applies to tropical maturation, and anyone who names a hard figure is naming the figure of one warehouse.

A twelve-year-old rum is not the same as a twelve-year-old whisky: in a tropical warehouse, the exchange with the wood and the loss through evaporation happen faster.

In the rum world, therefore, a conversion is sometimes used in which one tropical year counts for several Scottish years. That is a rule of thumb from the trade and nothing more: no legal standard sets such a factor, and no measured factor holds for all warehouses, casks and origins at once. Two twelve-year-old rums from two countries can therefore lie far apart.

A maturation period or age on a bottle of spirits may be stated in the EU only if it relates to the youngest alcoholic component in the bottle.

That rule is in Article 13 of Regulation (EU) 2019/787. For a blend that means: if it contains rum of five years, five years is the number allowed on the label, even if rum of twenty years is also in there. The regulation does not prescribe a minimum maturation for rum itself. It does state that rum must have at least 37.5 percent alcohol and that only caramel may be used to adjust the colour.

Of the 431 rums in the shop in Bathmen, 79 have an age on the label, from 33 brands from 26 countries, with a strength of 38 to 67 percent.

Of these, 42 bottles are twelve years or older. The origin of those 79 varies: Jamaica 11, Barbados 8, Guyana 8, Nicaragua 6, Panama 6 and the Netherlands 6. The entire rum stock comes from 40 countries, with Jamaica 49, Cuba 44 and Barbados 32 as the largest origins. That difference in origin says more about the taste than the number on the label.