Solera is a process for ageing rum by gradual blending of rums of different ages with the result that the finished product is a mixture of all these rums.
As the process was first developed by Spanish sherry producers, it is perhaps unsurprising that the main producers of solera rums are former Spanish colonies such as Colombia, Venezuela and the Dominican Republic.
The classic solera system requires a series of barrels stacked on top of each other.
The barrels at the bottom of the pile contain the oldest rum. The barrels in the next layer up will contain younger rum. The barrels in the third layer will contain even younger rum than those in the second layer, and so on. The number of layers of barrels can vary, but the age of the rum will always be youngest at the top of the pile and get gradually older as you move down the layers towards the floor.
When it has aged for the agreed time, some of the rum from the bottom layer of barrels (perhaps a quarter of the barrels' contents) is drained off to be bottled.
As this rum is drained off, it creates space for younger rum from the second layer of barrels to trickle down into the bottom layer of barrels. This in turn allows even younger rum from the third layer of barrels to flow down into the second layer, and so on. This will leave barrels on the top layer one quarter empty, so distillery workers top these up with new , unaged rum to ensure that the process continues.
If the solera process is done correctly, the barrels are never completely drained. This means that, even after decades of production, the bottom layer barrels might still contain trace amounts of the original rum used by the distillery when the process was first started.
By continually blending similar proportions of older and newer rums, the aim of the solera system is to produce a complex, flavourful rum to a consistent quality and style.
Very little of the world's rum is produced using a solera system, but the method and marketing of solera rum has attracted criticism.
One point of contention is the age statement. A solera rum could be a blend of rums aged 3, 5, 10 and 25 years, so should it be marketed as a 3 year rum, 25 year rum, or something else? Some critics say that any age statement on solera rum should be restricted to the age of the youngest rum in the blend.
If you want to try solera rum, well-known brands include Ron Zacapa 23, Santa Teresa 1796, Dictador, Matusalem Solera and La Hechicera.