Rum is one of the easiest spirits to make, since the laws and regulations that surround it are slack to say the least. The only real ‘hard and fast’ rule when it comes to rum is that it has to be made from sugarcane.

Sugarcane is a type grass; when you press it, the resulting juice has a sugar content of between 15-20 brix (15-20% sugar). It’s not often that you see crates of raw sugar cane in your local ASDA, but sugar cane products are readily available in the form of crystalised sugar. Different sugars will make subtle changes to the flavour of a rum, each type of sugar is unique depending on its production and origin.

You can also make rum from sugar cane honey (the juice of the cane boiled down and concentrated), or molasses.

Fermentation

Molasses is the raw material used to make the vast majority of the worlds rums. Quite simply, molasses is the bi-product of the sugar refining process. Once all easily obtainable sugar has been extracted from the juice of sugar cane, the leftover sticky black substance is known as ‘black-strap’ or molasses. Surprisingly it can be as rich as 50 brix (50% sugar), though usually it is around 20-30 brix.

These sugars are perfect for fermenting and the other compounds within the molasses provide adequate nutrients for the yeast to thrive.

Fermentation can last anything from 50 hours, right up to 2 weeks for rum. The hot Caribbean/Central American climate, that most rums are produced in, lends itself well to a speedy and efficient ferment, thriving in 25-30°C. Molasses needs first to be diluted with around four parts water to every single part of molasses (though every producer will differ slightly). The sugar level of undiluted molasses would be uninhabitable for yeast.

First, warm you molasses up in a sink full of hot water, this will make it less viscous. Pour the molasses into a fermenting bin and add hot water equal to four times the volume of molasses. The water will need to be hot in order to dilute the molasses sufficiently. Let it cool. When the mixture reaches around 35°C it’s time to add the yeast. Any wine making or, even better, champagne yeast will be up to the challenge, hydrate well before adding it, then give everything a jolly good stir to aerate.

At this stage it is advisable to use a hydrometer to measure the the specific gravity (or relative density) of the unfermented wort. The hydrometer will float at different levels according to the liquids density and its potential alcohol content. A reading of around 1.050 to 1.080, would be a desirable, as it indicates a potential to create 6-10% abv. Once fully fermented another reading can be taken, deducting that number from the original SG will tell you the final abv of the wash, with the help of this chart.

When fermentation is complete the liquid is a bit like a heavy porter, or rich liquorice wine, retaining little of its original sweetness. The sugar has been eaten up by the yeast and converted into alcohol.

This molasses wine is now ready to be distilled. As usual I have managed to get hold of some pictures of the process involved and I am able to share with you some of my thoughts on rum production…

Distillation

Most modern rums derive much of their flavour from the aging process. Often we associate the natural influence of American oak as the flavour of distilled sugar cane, but a lot of the time we are simply tasting the magical influence oak has on a relatively neutral spirit. There are of course exceptions (Wray & Nephew springs to mind), but many of our favourite brands retain little of their distillate character when it eventually comes to bottling.

Rum that is made in a column still usually has most, if not all, of is characteristics removed. It is essentially purified, much like a vodka. In fact many new make (unaged) rums could be legally sold as vodkas if the producer was inclined to do so.

Rum that is pot distilled (in much the same way as a whisky) tends to retain more of the flavours and aromas from the molasses or cane that it is made from. This artisan method of production is far less efficient than a column still, but it does often result in a more naturally characterful spirit. Retaining rich, resinous sugar flavours and usually a fair amount of liquorice too.

The strength of the distillate extracted from a pot still will depend on the shape and height of the still. The longer the neck on a still, the purer and lighter the spirit will be, this is because a long neck encourages reflux to occur. Reflux is a process of evaporation and condensation of spirit and water vapour that takes place continuously within most pot stills. As the fermented wash rises up the neck, the distiller controls the temperature at the head. A steady decrease in temperature from bottom to top encourages only light alcohols to make their way up and over the ‘goose’s neck’. The longer the neck, the greater the chance that impure low alcohols and water will never make it over and in to the condenser.

With this in mind, a pot still with a long neck can produce a spirit of anything up to 40%abv in the first run. This stuff wont be all that drinkable mind you, containing many of the soluble impurities from the wash as well as lighter alcohols like methanol and acetone. No,  the second distillation in pot still is where it’s at, further purifying the spirit and drawing off liquid somewhere in the region of 80% abv.

At this level the resulting liquid (when cut with water to 40% abv) doesn’t smell particularly nice. Plenty of harsh liquorice notes, and none of the sweet, buttery candy-floss tones that we would commonly associate with spirit derived from sugary nectar. But the process is not finished just yet, oh no no no!

The next part involves patience (and an oak barrel).

Ageing

The spirit requires ageing.

As I already mentioned, the vast majority of the rums available today go through an ageing process, sometimes only for a matter of days. The reason that producers do this is to positively alter the flavour of the distillate. I often liken oak barrels to inside-out tea bags. The wood contains flavours (cellulose, hemicellulose, tannins and lignins) that will interact with the spirit and, aided by a degree of oxidisation, have a massive impact on the aroma and taste of the liquid.

The surface area of a 5l cask is around 2000 cm² (2.5ml/cm²), comparatively an average industrial oak cask would have a volume of 200l and a surface area of 20,000 cm²(10ml/cm²). A barrel forty times the size has four times the liquid volume to surface area ratio.

In a tiny 5 litre cask, with a low surface area to volume ratio, the effect is noticeable in less than a day.

Below is a picture of rum extracted from a 5l cask after only a month ageing. The rum went in to the barrel crystal clear, but during its time in there it has picked up colour as well as soluble and insoluble compounds. An alcometer tells us that the spirit has an abv of 43%.

A few things to take note of:

1/ It’s cloudy. It seems that some of the compounds taken from the oak are insoluble in water/alcohol. You might suspect that the cloudiness is a result of fusel oils present within the distillate itself, but I can assure you that the spirit was crystal clear before entering the cask.

2/ It has a strange green tinge to it (we’re all thinking urine, I know), rather than the golden colour that we would normally associate with rum.

On a plus side, however, I can vouch for both its taste and smell. The barrel has performed a miracle act, converting some very stubborn odours into buttery, caramel, chocolate softness. The length of finish was once a sickening liquorice twang, now it is a soft, mouth-coating warmth, with just a touch of resinous sugar sweetness. It’s not the best rum in the world, but it’s flavoursome, interesting and, dare I say it, balanced.

So, how to get rid of the cloudiness?

Filtration

Let’s start with a simple mechanical filtration, a paper coffee filter should do.

As you can see, the paper filter has removed much of the larger debris, leaving a residue of brown… stuff… tiny bits of oak I’m assuming. But the spirit is still cloudy. Time for some more aggressive techniques, charcoal filtration should help.

Many of the white rums that we consume are in fact aged products that have been filtered in order to remove the colour. In many cases this is stated on the label: Havana Club Anejo Blanco, “aged white”. As with any other aged rum, this is done to positively influence the the flavour and aroma of the product, softening some of the more aggressive distillery characteristics. These white rums, that are stripped of their colour, are almost always filtered through activated carbon. See my previous post on filtration for more about this.

Activated charcoal is of course quite easy to get hold of, it’s the stuff inside any common water filter cartridge.

I’m going to give my filtration an even better chance of removing the cloudiness by first cooling the spirit right down in a freezer. In the spirits industry this is called ‘chill filtering’. It works on the basis that many of the fatty acids, esters and proteins present within spirits are insoluble at lower temperatures. By chilling the liquid down the filtration process is more likely to be effective. You might have seen certain whiskies advertising themselves as ‘non-chill filtered’. This is because many whisky aficionados believe that the removal of these insoluble compounds is actually detrimental to the taste and aroma of the final product. A non-chill filtered whisky can often be spotted by the addition of water, as many of the compounds that would be removed by the process are also insoluble in lower alcohol solutions. Chill filtering is usually performed at around 0ºC.

And the result? It’s still a bit cloudy…

So the final product is a liquid that has lost much of its colour through the filtration process, and certainly a degree of its cloudiness, but not all of it. I would wager that more filtering, perhaps through a larger filter, would remove all of the haze and probably most of the colour. Or perhaps a laboratory grade filter? Or maybe chilling down the charcoal?

Maybe i’ll have a think about it whilst sipping on a nice ‘Dark and Stormy Clouds’!

March 29th EDIT: Since January I have had a few conversations with people about cloudy rum. Jamie MacDonald who is an ambassador for Grand Marnier and Appleton Estate and also the owner of Raconteur in Edinburgh had some interesting insight. He hasn’t made rum as such, but he has infused bitters and the like and repeatedly found that the addition of raw cane sugar causes his creations to go cloudy. I did indeed add a small amount of cane sugar to my rum during the ageing process, it seems that this may be the culprit.

This is reassuring, since it not only gives an reason to the problem, but also removes any suspicion of something dangerous being present within the rum. Anyone know what the craic is with raw cane sugar and alcohol?

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