Cask & Climate

How is Demerara Rum aged, and how old can it legally be labelled? The warehouses stand at sea level, at around 24 to 32 degrees Celsius and roughly 70 percent humidity, according to the geographical indication specification. Maturation mostly takes place in white oak casks. In the industry, these are often used bourbon barrels that lend the rum vanilla notes and sweetness.

In this climate the wood works faster than in Scotland. The rum soaks into the staves and seeps back out, water evaporates, and so does alcohol. For tropical warehouses, the trade press often cites around eight percent loss per year, compared with about two percent in Scotland. So when a cask is opened after many years, what's left is considerably less than what was originally filled.

This climate has given rise to a popular rule of thumb: one year in the tropics is said to count as three in Europe. It comes from marketing and isn't chemically precise, since evaporation and wood interactions behave differently. What's certain is that tropically aged rum, at the same age, turns out bolder and darker than one matured in a cooler climate.

Important for the label: within the EU, an age statement may only refer to the youngest component in the rum, and maturation must have taken place under the tax supervision of a member state or an equivalent control regime. For single-cask bottlings, a vintage — the year of distillation — is usually also stated, as with a 1990 Port Mourant or a 1998 Uitvlugt. These two figures don't mean the same thing, and the vintage alone doesn't reveal the age at bottling.

Some casks don't mature in Guyana but travel to Europe instead. Independent bottlers such as Velier, Cadenhead or Silver Seal have let old marques continue ageing in cooler warehouses, where maturation is slower and losses are smaller. This produces bottlings that may sound similar in age but can taste quite different in the glass. Colour offers little help here, since it can be adjusted with caramel colouring.