Using an Air Still to Distil Rum

While I was working at the Coal & Cotton pub, I had a chance to help out with developing their spiced rum and dark rum recipes. We did a few test distillations in an air still to try out our recipe ideas.

Adam, the distillery manager, purchased some bottles of 37.5% abv white rum to charge the air still with. The air still was exclusively used to experiment on different rum recipes. Later, we intended to scale up the recipes and do the main distillations in our 50L hillbilly still, Tessy.

Initial Rum Distillations on the Air Still

The air still has a capacity of 4L, but we charged it with 1L of white rum only, which isn’t ideal since you run the risk of running the air still dry. We purchased the white rum for around £9  per litre, so if we filled the air still with 4L of rum it would make for a pretty expensive experiment (4L x £9/L = £36).

We measured out the botanicals for our spiced rum and our dark rum recipes. The initial recipe for the spiced rum included: star anise, cloves, black peppercorns, vanilla pod, ground ginger, cinnamon bark, allspice, nutmeg, lime peel and grapefruit peel.

Our initial recipe for the dark rum included: kola nut, raisins, orange peel, dried lime peel, vanilla bean pod, black peppercorns, cloves, nutmeg, allspice and cinnamon. The kola nut is very interesting and something I hadn’t seen before. It is a caffeine containing nut from trees of the Cola genus. Kola nuts have a bitter flavour and are chewed in many West African countries. They are best known as a flavouring ingredient, and a source of caffeine in cola beverages. Reportedly, kola nut extract was originally an ingredient in Coca-Cola, but it no longer is.

Before I arrived at the distillery, Adam had done some experiments with the spiced rum recipe. I edited his recipe, and helped to develop the dark rum recipe. We distilled the dark rum recipe first. In the air still, we added the white rum along with the botanicals. Adam also put in some ceramic shards, which he said helped the still heat up faster. I know you can buy ceramic boiler enhancers which are supposed to prevent wash from frothing over, but since were charging the still with a spirit I didn’t think this would be an issue. Wash, which is basically beer, has proteins and dissolved carbon dioxide in it. Since we used distilled white rum, which didn’t have solids, I did not think the ceramic shards were necessary. However, we did use the shards in our air still distillations.

I turned the air still on. When the first drips came out, I turned the air still off to allow the botanicals to macerate in the liquid for 15-20 minutes in order to extract more flavour from them. After the waiting period, I turned the air still back on to continue spirit collection. We collected the spirit until it no longer tasted nice coming off of the air still. This happened to be around 28% abv. In total we collected 500 mL of spirit at 69% abv. Then Adam used regular tap water to dilute the rum down to 40% abv. In the kitchen upstairs, Adam made his own caramel using white sugar and a touch of water. He poured 50mL of this homemade caramel into the dark rum. We repeated this process for the spiced rum recipe.

We did a taste test and my updated spiced rum recipe wasn’t well received. Everyone kept saying that they liked Adam’s original recipe more. Since they liked Adam’s original recipe for the spiced rum, we decided to use that recipe but with a few minor tweaks.

Second Rum Distillations on the Air Still

Adam’s original recipe had a lot of star anise in it. This gave the rum a strong star anise or liquorice flavour which I wasn’t a fan of, but then again, I dislike black liquorice in general. We decreased the amount of star anise a little bit. As well, we decreased the amount of vanilla bean pod. In Adam’s original recipe, he used ½ a vanilla bean pod per 1L of white rum. Vanilla bean pods are incredibly expensive, so it wouldn’t have made sense to scale that up. We would have had to buy 25 vanilla bean pods, or spend £40 for just for one ingredient in our rum recipe. A few more rum experiments later, and we settled on our two rum recipes. We put homemade caramel into both of the rums. The caramel gave both of the rums a pretty yellow golden colour and a sweet finish.

Adjusting the Rum Colour

Adam wanted to experiment with the colour of our rum samples as well. We tried soaking whisky cask oak chips to impart colour and flavour to the rums. I think Adam accidentally ordered the wrong kind of oak chips though, as those chips were for using in a barbeque grill. The label even said “whisky flavoured chips”. The key word being flavoured. We then ordered some proper charred oak sticks off of Amazon. While it did impart some colour to the rum, it obviously gave the rum an oaky flavour which wasn’t desired since we were already happy with the flavour.

At that point, we started trying all sorts of different things out, such as macerating raisins in the rums and adding natural food colourants. They wanted the dark rum to be black like Kraken, so Adam ordered black food colouring. The black food colouring was a lot more viscous than we expected. Adam put three drops in the paste. It was so viscous that it turned the rum a murky black colour. Adam said he liked the colour of it which surprised me. While from afar, the colour looked similar to Kraken rum, if you actually hold a bottle of Kraken up to the light you can see the liquid is actually clear and dark brown in colour. In comparison, our rum was a murky black colour with a green tinge.

The dye didn’t seem to be right, so I suggested that we instead add some of the natural red food colouring that we use for the strawberry gin recipe. The red food colouring turned the rum a dark amber colour which I thought was nice. Th colour was also quite distinct from the colour of the spiced rum. Later, we also found a less viscous kind of natural black food colourant. If used in tandem with the red food colouring, these colourants should turn the dark rum a super dark brown colour, more similar to a Kraken rum.

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