Though it may seem a rather derogatory way to talk about a noble spirit rum, perhaps uniquely, is a by-product. It first appeared in the 17th century as a result of sugar planters finding a way in which to get rid of (and make more money from) molasses, the residue left over after sugar has been made. This thick, black, ironrich, bloodily-scented gunk may not have had any more sugar crystals to give,but it was still rich in the stuff and therefore if it could be made to ferment could produce alcohol which, when distilled, would give a spirit.This spirit in turn could be given to the slaves and indentured labourers or sold on for more profit. In simple terms this is still what happens today, although few of the distillers in their hightech plants would thank you for saying so.Rum still starts life as molasses.(Unless that is you are making rhum agricole, see below).Originally each estate would have had a distillery attached to its sugar mill, but the consolidation and decline of sugar across the Caribbean means that many distillers now buy their molasses from the bulk producing countries such as Guyana and Brazil.Because the sugar level of molasses is high it has to be diluted before fermentation can take place. In general the ferment is rapid and violent, mainly due to a combination of lots of sugar and a high ambient temperature.This means that distillers have to use (or develop) yeast strains which can work effectively under these conditions.Various strategies such as using cooled fermenters, or semi-continuous ferments are used.Mostly the wash of around 7% ABV is ready after 36 hours, but there are notable exceptions, mainly in Jamaica.Here ferments can be as short as 36 hours or as long as two weeks.In simple terms, the longer the ferment the more acidic the wash and the higher the concentration of esters.Want to know where Jamaican rum gets its pungency from? Look to the fermenters and to the dunder pits outside the distillery which contain the spent lees from previous distillations which can be added to the fermenter. Want to know where sourmashing came from? Look to Jamaica.Distillation can take place either in pots stills or column still setups.The latter produce light rums (and tend to come from short ferments), the former make heavy rums (often from longer ferments).Many producers will use both styles in their final blend.The pots, while similar in shape to those in Scotland (indeed many come from Forsyth’s) tend to have an additional element to them: retorts.These small copper vessels allow the distiller to produce this final spirit in one pass rather than two.Typically, they contain the low and high wines from the previous distillation.When the vapour hits the first retort it releases the alcohol in the liquid which then concentrates the strength of the resulting vapour.This is then repeated in the second retort then the vapour is condensed, separated and collected.The spirit,both light and heavy, can either be reduced and bottled as white rum or,more commonly, aged.The best whites rums (Bacardi, el Dorado, Elements Eight, Angostura) are all aged.Barrels are most commonly ex-bourbon barrels which add their flavours of vanilla, coocnut, cherry, spice to the spirit.Virtually no finishing takes place.. the one exception is Doorly’s XO.Richard Seale is also experimenting with aging in Madeira casks.What no Caribbean distiller can avoid is the massive losses which take place in tropical aging.Whereas a cask of malt whisky will lose 2 per cent in volume every year, a rum aged in the Caribbean will lose up to 8 per cent.That’s a lot of happy angels and sad distillers.In simple terms this means that five years of aging in the Caribbean is the equivalent of 12 to 15 years in Scotland.Bear that in mind when looking at age statements.A 15 year old rum is a venerable beast indeed.Rhum agricole is a totally different character. For starters it uses cane juice not molasses, then it is distilled to low strength in a single column strength and finally is aged (most commonly) in ex- Cognac barrels.All in all rum’s a pretty complex by-product.