Making Rum With Molasses (Improvements-Journey Into Rum Part 6)

In the previous “Journey Into Rum” posts, we fermented our molasses wash in the iStill 2000L fermenter, and then distilled the wash in batches. After the first distillation, the low wines had a slightly sulphury, burnt, and plasticky flavour. These negative flavours were removed during the second distillation, and we were left with a pleasant white rum. However, that doesn’t mean there isn’t room for improvement in our production process. In this final post, I will go over how we fine-tuned our white rum production process at the Shakespeare Distillery.

Change #1- Rum Fermenter Cleaning

After the third “Journey Into Rum” video was posted on YouTube, my boss received an email from the founder of iStill, Odin, who gave us some advice on how to produce our rum with the iStill. This just goes to show you never know who is going to watch your videos on YouTube! One of the first things he said was that we never need to use cleaning agents on the iStill fermenter. All we need to do is rinse it with water using a pressure washer.

Change #2- Molasses Transfer

Initially, we stuck our transfer hose into the top of the molasses Intermediate Bulk Container (IBC). We only did this because the fitting didn’t arrive on time. Since the Camlock fitting had now arrived, we attached the hose to the bottom of the IBC. Gravity did most of the work to move the molasses out of the IBC and into the pump.

Change #3-Fermentation Temperature

In our first large-scale fermentation, we brought the water temperature up to 34°C before adding in the molasses. We tried to use the iStill heating element to heat up the water, but that took 4 hours to do. It didn’t seem like a good long-term solution. Later on, we just heated up some water in the istill and then pumped it over to the fermenter. Also, instead of aiming for the water to be 34°C in temperature, we only aimed for it to be 20°C. During fermentation, heat is produced and the temperature of the molasses wash gradually rises on its own anyways.

Change #4- Eliminating Citric Acid

Odin said that we should try not adding citric acid to our molasses wort to see how it would ferment. Our reasoning for adding the citric acid was that during our small-scale rum tests, we enjoyed the taste of the spirit more when the starting pH of the wort was lower. The citric acid was added to the molasses wort to lower the pH, making the wort more acidic. While this worked well in our small-scale tests, the flavour of the rum in our large-scales tests were extremely different. That was to be expected since we did our small tests using copper alembic stills, while our large-scale distillations were done on a stainless steel iStill. It just goes to show how important still type is in impacting the spirit’s flavour profile.

Change #5-Higher Specific Gravity

While we were racking our brains on how to improve our production process, I thought to myself, you know what would be really helpful? If we could talk to another English distillery that also uses molasses and iStill equipment to make their rum. I went on Google and found a distillery that fit these criteria. After I uncovered the name of that distillery’s head distiller, I went on LinkedIn and sent him a message. Later, we chatted for half an hour on the phone, discussing the production processes of both of our rums. Interestingly, he also performed two distillations to produce their rum. He was also surprised that our starting specific gravity of the molasses wort was so low. He suggested that we try a higher starting specific gravity, closer to the 1.070-1.080 range to increase our alcohol yield.

A quick refresher on what specific gravity (SG) is. Specific gravity is the ratio of the density of a substance to the density of a standard, in this case, water. Increasing the starting specific gravity of the molasses wort means that we are making it even denser than water.

How do we make it denser? We just add in more molasses. Adding in more molasses means we have more fermentable sugars. More fermentable sugars means that we will produce more alcohol, and more alcohol means that ultimately, we will have more product to sell. You can see why it makes sense, business-wise, to keep trying to get a higher and higher starting specific gravity.

Change #6-Adding Copper

In our first large-scale distillation, we only had a single copper waffle in the still. We happened to have some extra copper packing material lying around the distillery, so we decided to put all of the extra packing material in a small muslin bag and tie it to the still column along with our single copper waffle. After each distillation we took out all the copper, cleaned it, and put them back in the still for the next distillation.

Change #7-Changing iStill Modes

The iStill has a lot of different functions and modes on it. David continually tweaked the settings on the iStill to see how that would change the distillate. One of the things he discovered was that he could set the pot of the iStill to pre-heat to any temperature. Now when he comes into work he can start collecting the spirit right away instead of waiting for the still to pre-heat.

Change #8-Removing Solids

There was a lot of discussion about whether the solids in the wash were sticking and burning to the still’s heating elements. I thought a possible solution was to open the bottom valve of the fermenter and flush out any dead yeast and other solids that had settled to the bottom. We tried to open the bottom valve once. I expected a thick and sludge-like liquid to come out, but the consistency was more similar to water. Clearly, the yeast was still suspended inside the liquid.

We could have added a fining agent, like Turbo Clear, to the wash. This would have removed the majority of yeast cells, solids, and other unwanted compounds from the wash. Unfortunately, we never got around to trying this idea out.

We also wondered whether it was necessary to invest in an agitator system that could be put inside the still. The agitator would keep the liquid moving throughout the distillation to prevent solids from sticking and burning onto the heating elements. However, after eliminating the citric acid from our recipe and changing some settings on the istill, we noticed a big improvement in the flavour of the spirit. It felt like there was no real need to invest in an agitator system anymore.

Continuous Improvements

All of the changes we implemented simplified our rum-making process. While these changes produced a better smelling and tasting spirit after just one distillation, we all agreed that the spirit still tasted best when it was distilled twice rather than once.

The iStill is advertised as being able to distil a great product in just one distillation, however, for our rum production process we decided to stick with two distillations. David continues to constantly adjust the iStill settings and make other small changes to see if he can make a rum in one distillation.

You might be wondering whether constantly making changes to our production process (such as adjusting the settings on the iStill) could change the character of the white rum too much from batch to batch. Yes, these constant changes can produce a very different rum from the one we want. Luckily, we are not only producing a white rum, but a spiced rum too. If the the taste of a batch of white rum is significantly different, we can always set that batch aside and turn it into spiced rum.

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