iStill Fermenter Cleaning (Journey Into Rum Part 2)

Check out the first Journey Into Rum Post Here

We continued our Shakespeare rum production project by assembling and cleaning the brand spanking new 2000L iStill fermenter. It was purchased to ferment our molasses wort to turn into rum. It arrived almost fully assembled, there were just a few bits and bobs that we needed to figure out how to install.

Assembling the Bits and Bobs

David assembled and inserted the pH probe through the back of the fermenter, and then began testing the tilt sensor. This sensor tells us the specific gravity of our molasses wash. Specific gravity, also called relative density, is the ratio of the density of a substance to that of a standard substance. In this case, that standard substance is water.

We were going to make sure the tilt sensor was reading everything accurately, so I filled a bucket with water. Theoretically, when the tilt sensor goes into this bucket of water the specific gravity should read 1.000. It did, which was great as we could then be confident that our readings from the tilt sensor were correct.

If the liquid we measure is denser than water, the specific gravity will be higher than 1.000. And if we put it in something less dense than water it will be under 1.000. Since our molasses wort was packed full of sugars, it was definitely denser than water. You may have figured this out by now, but since specific gravity is a ratio, the number is also unitless.

Next, we inserted the Bluetooth sensor into the iStill fermenter. The Bluetooth sensor relays data from the tilt sensor to the computer screen at the front of our iStill fermenter. In order to get the sensor fitted in, someone needed to go inside to tighten it in. It was clearly a task made for me to shine! It isn’t often that being short and small is considered an asset, so I had to make the most of my moment to shine. Lastly, David attached the agitator into the still. This agitator helps mix the liquid in the fermenter.

The iStill Fermenter’s First Clean

David and I filled the iStill fermenter with 100L of warm water at 27°C. To get this much water to temperature, we mixed tap water(~10°C), with kettle boiled water (~100°C), and warm water from the sink (~50°C). These three sources of water were mixed together until we had 100L of water at 27°C. There was actually a heating element inside the fermenter. However, it was very high inside the fermenter. The 100L of water inside it wasn’t anywhere close to the heating element.

Next, we took out our eccentric screw pump and attached two hoses to it. One hose connected the bottom of the fermenter to the pump. The other hose ran from the pump to the top hatch of the fermenter. At the hose end by the iStill fermenter, we inserted a hose spout, so someone could stand near the hatch and spray liquid out.  David and I put on our personal protective equipment (PPE), and then took out 6L of caustic solution. The caustic solution had a pH of 14. We put it in the iStill fermenter with water to dilute it from a concentration of 32% to 2%.

After recirculating the caustic solution for 20 minutes, we emptied the caustic solution into the drain. The pH in the vessel was now 14 (very basic), so one of us stood at the top hatch to spray water all around until the water that came out of the drain was neutral. I tested the water flowing out of the drain with a pH meter to make sure the pH turned back to 7. This took about 20 minutes.

Checking in the Small-Scale Fermentations

After five days, the small-scale fermentations we prepared were down to a specific gravity of around 1.014. They started at 14 °Brix. I distilled these completed fermentations in copper alembic stills that we had in the gin laboratory room.

I did a stripping run in the stills, and collected the spirit until the spirit coming off the still was only 7%abv. Then, I re-distilled the collected spirit in a spirit run. I collected the distillate in little glass beakers so we could decide which parts of the distillation we wanted to include in our final rum. It was really hard to say which one of the experiments tasted the best, mainly because when we were making the cuts during the spirit run we cut them all at different points in the distillation.

It wouldn’t have been fair to say that one experiment tasted better than the other since cut points also make a huge difference to the quality of a spirit. For our 2000L molasses fermentation, we decided to use the same procedure as for experiment #31. We just scaled everything up for the big iStill fermenter and hoped for the best.

You can read the third Journey Into Rum Post Here

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