Making white rum, and therefore mojitos

First, acquire a beverage

The sacrifice

This album is going to document making a batch of white rum, my style. The drink pictured is what I want to be making on the other side – a mojito, which according to me is made with muscovado sugar, before anyone comments on the colour 🙂

This has a few implications at the outset. I want to make a white / silver rum, so I need to ensure it is nice and smooth off the still, as it won’t get the benefit of extended aging on oak. It also means that I need to aim for a light and fruity rum that still has enough flavour to shine through when mixed with plenty of lime and mint.

I’ll just go ahead and apologise now for the large amounts of text in this post – this was actually an Imgur album originally, but I couldn’t stand the wall of text it made and so had to start a blog.

Then, make a mess

I normally boil up the sugar sources and nutrients for my rum on the stove in my indispensable brew pot.
On the left we have my molasses drum. I take this into the nearest farming supplies store (which is really far away because I live in the middle of a city) and fill it up with bulk, feed grade blackstrap molasses. Blackstrap molasses is a byproduct of the sugar industry, and more or less consists of whatever is left after the sugar mill has extracted as much sugars as are economically viable. It’s about 50-60% fermentable, depending on the local economy and season. Molasses this concentrated is pretty strong stuff, and is really too heavy to use alone for the sort of rum I want to make, so I’ll be adding some plain white sugar to the mix as well.
Cheap white sugar
Cheap and cheerful sugar, used by a cheap and cheerful distiller. As I alluded to in the above paragraph, by changing the ratio of various ingredients, I can influence my output characteristics (duh). One of these ratios is the amount of sugar to molasses. This varies a lot depending on your molasses source. In some places, it may be cheaper to buy “fancy” or “table” molasses (not as processed, lighter flavour, more fermentable sugars), and you might not need any sugar in the mix for a middle of the road sort of rum. The more sugar added, the “lighter” and “fruitier” the end flavour is, and more molasses added ends you up with a deeper, more complex, almost buttery rum.
When deciding the ratio, you need to consider what you’ll be doing with the rum. I’m planning on leaving all of this white, i.e. no oaking, so I don’t need a big flavour backbone to stand up to oak or spices. I’ve settled on about a 1:1 ratio of sugar to molasses. I’d go as high as 3:1 for a dark, oaked rum. Using raw or brown sugar is a whole other bag of worms, so I’ll leave discussing that out of this.
Other ingredients
There are a couple of other ingredients that really help out a rum ferment. Molasses is often quite low in various trace elements that yeast like, so I add some yeast nutrients to help them along. A couple of tablespoons of diammonium phosphate (often sold alone or in a blend as “yeast nutrient salts” or similar in brew shops), half a teaspoon of magnesium sulphate, and a couple of B complex vitamins.
Many distillers use boiled (i.e. dead) yeast, as yeast are happy little cannibals and will feast on the exploded cells of their departed brothers and sisters.
It is common to adjust pH with an acid addition as well, but I’ve got something to deal with that later in the process.
Finished sugars and nutrients
This is now a “high gravity” (lots of sugars dissolved in it) rum “wash” (what rum distillers call unfermented liquid instead of wort). This will now be cooled, and diluted with water and dunder (more on that later).
Into the fermenter
I ferment my washes for spirits in 75L-ish tighthead drums. They’re foodgrade and about $5 each, readily available, easy to work with, and movable (just) when full if you’re a reasonably strong person.
Introducing the dunder pit, aka my pet infection
Dunder is spent wash from rum production, or what’s left in the boiler after alcohol has been extracted in a “stripping run” (fast pot still run with no cuts to strip the usable alcohol out of a wash).
There are a lot of unfermentable sugars and proteins in a rum wash due to the nature of molasses, so there are lots of goodies still in the dunder, and in traditional rum production, a “dunder pit” was developed, where dunder is allowed to become infected. The bacteria eat a lot of things that the yeast cannot, and produce esters that enhance the final profile of the rum.
This infected mess is added back to the wash, and the amount you add controls wash acidity, and also influences the final flavour profile. Recycling dunder is essential in crafting a fine rum (IMHO), but aging it like this isn’t absolutely  essential, I’ve made many a fine rum with fresh dunder hot out of the still boiler. It does add a certain special something though, buttery / floral flavours to my palate. This dunder has been, well, rotting in the sun for about 6 months now. It has been all sorts of colours, but seems to be settling out now.
Racking dunder into the fermenter, trying not to breath
I have a dedicated bit of hose for this that stays a long way away from the rest of my brewing equipment. I’m just eyeballing it, but depending on your local water profile and end flavour requirements, you might use as little as 20% dunder by volume if it’s very ripe, or as much as 40-50% if it’s young and hasn’t been recycled many times. Too much and the acidity will slow and eventually kill the yeast.
Controlled fermenting environment
I ferment in temperature controlled fridges. The controllers are cheap on ebay, and fridges are virtually free if you aren’t picky. My rum yeast (EDV493, isolated from sugar cane, hell of a yeast) likes it hot, so the fridge is warmed up to 30C. The Yeast will be pitched at this temperature, but then It’ll end up cooling as the fermentation produces heat – this is a very, very vigorous yeast.
Making a yeast starter
In the warm fridge, my EDV493 has been bred up from the yeast bank on my DIY stir plate. This was about half a litre of very thick slurry in a roughly 2L starter – probably enough to not really need a starter for such an aggressive yeast, but it had been in the fridge for a while, and I wanted to get it nice and active.
My yeast, fresh of the stir plate. This is third generation yeast.
Yeast Pitched
The fermenter topped up with water (this provides one last opportunity to get the wash at the correct pitching temp), and then with much grunting, I get the fermenter into the fridge, where it will ferment out in a few days.
If you are making rum, you should be aware that a high finishing gravity is to be expected, normally around 1.025, due to unfermentable sugars and the likes in the molasses. A lot of novice distillers get a bit worried that their wash has stuck, so worry not. The fridge will then be turned on, and the yeast will flocculate (drop out of suspension). EDV493 has extremely good flocculation.
Stripping run -pot still
Half the wash is racked to the boiler. Molasses is notorious for foaming in the boiler and causing the still to “puke”, which is a real pain in the ass, so plenty of headroom is left. Some people add antifoam agents, I don’t bother, as two runs per ferment works very well for me.
A stripping run is a simple pot distillation, if you want to read more about it, see my Making Gin album on imgur (this picture is actually from there… I forgot to photograph my rum stripping run but it’s exactly the same).
Spirit run – detuned reflux still
My rum distilling process is a little bit different to many distillers. I add the “low wines” (uncut product of the stripping run at 30~40%ABV) back to the boiler, and then add the remainder of the wash from the fermenter. I then put on my vapour management reflux column, but with only about a third of the packed column, and with a restriction under the reflux condenser that allows me to divert more vapour to the product condenser (instead of returning it as reflux) than is usual for this type of still.
Warning – science follows. Skip if you aren’t interested :).
A crash course in packed reflux stills: The column is packed with a medium (in this case copper mesh) to provide surface area for mass exchange between upcoming vapour and reflux (returned condensate from the top of the column). This effectively provides multiple distillations and increases the separation of components in the distillate.
If I ran rum in the full column, it would be too efficient for my tastes, and I’d get no flavours in my final product. Or, more accurately, the flavours will be concentrated in the undesirable parts of the distillation run instead of being smeared through into the “hearts” of the run. That would make me deeply unhappy, and my mojito would taste like it was made with vodka instead of rum, which would make me even more unhappy.
So why then am I using a still which encourages separation instead of the simple pot still which is also at my disposal, I hear you ask? Two reasons, the first of which is esterification. Yes, that’s a real word. For the complete rundown, look at this wikipedia article. If you aren’t that interested in chemistry, let me break it down – by refluxing (returning all of the boiled vapour back down the column as liquid reflux) for a period before taking off my distillate, I can create esters, which are delicious, and will give me lovely floral, banana, and coconut flavours as well as a good buttery-ness. I can’t do this with my pot still.
The second reason is that, given my goals (a delicious mojito), a little bit of separation is a good thing. If I wanted a deep, dark rum to put to sleep on oak for a couple of years, then this would be inappropriate and I’d be better off with a pot still run, smearing all the different components together, which, on oak, would mellow out into a nice, complex rum. However, to get a smooth drinking product straight off the still, a little bit of reflux is acceptable, or even desirable.
For the operation of this slightly unusual setup, I heat up the still, then leave it under total reflux with a higher than normal heat input for about 90 minutes, then open the valve fully and collect the spirit run as if I was running a pot still.
End of the run
By the time that the thermometer is reading 91 C, I know that the boiler is almost completely depleted of alcohol (if there are any distillers out there saying “what, that’s too low”, Remember this is a reflux column).
I can tell this by working backwards off an ethanol/water phase diagram and the number of theoretical plates in my column, if anyone cares!
The practical reality is that I’ve probably already collected several bottles of “tails” that will be excluded from the drinking product, but will be recycled back into future batches, and with little ethanol left to recover, it’s time to shut down.
Collection bottles; cuts
Ignore the bottle of starsan, bits of still and other brewing paraphernalia, and pay attention to the row of bottles. Those contain the whole run, in order of collection.
The left hand bottle is the “foreshots”. These will be thrown away, or used as a cleaner round the house or for sterilising, or something. These are not recycled to prevent a buildup of undesirable cogeners in future batches. It is often mistakenly said that these contain methanol, but actually they’re chiefly esters like ethyl acetate mixed with ethanol. Methanol is not a concern for beverage distillers.
The second two bottles are the fraction called heads. These still contain a prohibitive amount of cogeners to be included in the potable product from this run, but can however be put aside as “feints” to be added to future runs to increase yield and flavour. Heads sometimes smell quite nice, especially rum heads, but there is a chemical, acetone bite that can’t be missed. Harsh tasting spirits often have been cut badly, including too much heads.
The next four bottles are the “hearts” cut – this is the good stuff, mostly ethanol, but with enough cogeners smeared through from fractions on either side to make our rum… rummy… Center hearts normally tastes almost neutral. It is a lesson hard learned by many distillers that the esters that provide flavour are really components of heads, and are like condensed hangover. Learning to place cuts between fractions so as to prevent hangovers and still get good flavour needs experience and patience. This fraction will be diluted to 40% before drinking for safety reasons.
The last two bottles are “tails”. These are under represented here, because the nature of a reflux column suppresses most of the tails (pot stillers reading this will have noticed that I stopped collecting at 91 C, which is about 60%abv, much higher than you would on a pot still). Tails contain a lot of fusel oils and higher boiling point compounds, and can taste and smell sort of like cheap soap and mint mixed together from a reflux column, or like wet cardboard or wet dog from the more dilute tails of a pot still. This fraction will be put into the “feints” container with the heads to be recycled into a future batch.
The cut points in a spirit run are best established by taste, smell, and sometimes feel. There are no hard and fast temperature or strength rules, as each still, recipe, goal product and even each distiller/blender will have produce or require different results to the next.
This is the hardest part of distilling to get right. True master distillers can cut straight off the still, but personally I find I get better results after airing the run out for a couple of days first.
So then, how about that mojito
I muddle a sliced lime with a tablespoon of muscovado sugar (dissolves easy, tastes great), then clap a handful of mint leaves and very lightly muddle them in so as not to break up the leaves too much. I then add ice to about halfway, add my measure of rum, almost fill up with soda water, stir to get the lime, rum and sugar off the bottom, then top of with more soda. Drink through a straw.
Well there you have it. Rum was made, and it is good. To learn more about this sort of thing, check out homedistiller.org/forum and artisan-distiller.net for advice and info. If you embark down this road, be aware of your local laws. I’m in New Zealand, where this is a legal hobby. And the sky hasn’t fallen in since it was legalised in 1996, either, but that’s another story. Cheers.

6 Responses to “Making white rum, and therefore mojitos”

  1. 1 Herbert_the_Pervert
    June 9, 2011 at 8:07 pm

    What kind of hose connecters did you use to connect your cooling lines to your potstill?

    • June 9, 2011 at 8:20 pm

      Hey, I just use garden hose connecters. They only take a moment to set up or disconnect, and then the cooling lines are very cheap and available from anywhere. On my new still I might use a wider barbed fitting, it’s going to take more power so should need more flow. Cheers.

  2. 3 Bruce
    June 9, 2013 at 11:26 am

    My single most favourite web page on the Internet!!!!!!
    I’m a Texan living in Australia. I visit north island a lot with work.
    Would LOVE to brew a batch with you so I can see it first hand.

  3. 5 Richie
    July 2, 2013 at 5:04 am

    Hey I’m in nz building a still at the moment, where did you get your $5 ferment barrel from? Cheers

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