What we post here is an account of iStill’s CEO, Odin, helping out a distiller that has difficulty making good gin with his still. Mind you, the still he uses is not an iStill, but a piece of equipment made in China, but Odin decided to help out a fellow-distiller anyhow, by analyzing his set-up, coming to conclusions, and giving advice on how to solve the issue.
There are two reasons to post this on the iStill Blog. First, it can help create awareness that there are many poorly designed stills out there. And if you end up buying or “designing” one, you might find yourself in a bad situation, where you cannot achieve the product quality you aimed for. Let this iStill Blog post serve as a warning. Secondly, this post shows that still design is a science, based on facts, and not something artsy-fartsy, romantic, close to magical, based on opinions.
The problem and the set-up
The problem the distiller had? Some of the flavors he was looking for didn’t come over well enough in his gin. He described the result as “less than elegant”. The distiller informed Odin that he runs a 100 gallon, steam powered Still Dragon, that the run takes 6 to 8 hours, and that he uses a potstill configuration with a 2 inch riser. The distillery is located at the high altitude of 6,000 feet above sea level. Here’s how Odin, despite not having a whole lot of information to go by, analyzed the situation, came to a conclusion, and gave his advice on how to solve the problem.
“So, quite honestly, there is not enough information for me to go on. But guessing my way forward, here is what could happen. Some calculations first, then a conclusion and maybe some advice that could help you manufacture a solution. 100 gallon system = 400 liters. I work / think in metric, hence the conversion. Not sure if that is gross or net capacity, but as most manufacturers advertise gross boiler content, I am going to estimate 300 liters net capacity. Now, I will bring up the numbers of the iStill 500. Why? Because it is most comparable in size and optimized for perfect vapor speed management (more on why that is important later). With us, 500 means 500 liters net. So your system is smaller and matches up to 60%. Looking at your run times, well, there seems nothing wrong there. Depending on the gin we run, 8 hours could be what we’d do with the i500 as well. So that’s good for comparison.
My design is directly fired and insulated and around 90% energy efficient. I estimate an uninsulated indirect design to be around 50% efficient. So my guess is that you are probably throwing the same kind of power (gross) at your unit as we do with ours. Your boiler content size is smaller than the i500, but your set-up being less efficient sorta compensates for that. Efficiency answering the question of how much of the gross energy input is actually used to distill (vs. heating up your distillery). Why the above line of thinking (and its outcome) are important? Because it tells me that the amount of vapors produced in your unit (for instance in liters or gallons per second or minute) are relatively equal to my set-up. So that part is fine. Relatively meaning that your 60% net boiler size is matched by overall lower net power input that seems to be at around 60% of what I would run.
Your gross power input might be the same as on my system. Your net power usage for vapor production is in line with your unit holding net 300 liters vs. mine holding 500 liters. Your set-up probably creates 60% of the vapors when compared to my design.
Time to move on from power and boiler and overall system efficiency to the column. The iStill 500 that I choose as a comparison has a 5 inch column. That’s 12.5 cms (again, I am metric). So the radius is 5.5 cms. Compensating downwards from 6.25 because of the thickness of the column wall and the fact that the iStill 500 column is packed, which eats away 10%. Now, what is the surface area in my column, were we to cut it in half and look down into it? It is 95 square cms or about 16 square inches. Your riser is 2 inch in diameter. Let’s say 1.8 net. This means the surface area in your riser is only 2.55 square inch. That’s only 16% of my (optimized) design. Why is that important? Here we go:
With some assumptions, and based on limited information, I concluded, in the first paragraph, that your set-up produces roughly 60% of the amount of gas (liters per minute or in gallons per minute, that does not matter) than my design does. Expecting you to have adequate cooling in place to knock all gasses back down to liquid phase via your product cooler, this merits the following assessment: the vapors in your set-up move WAY too fast. Say that given a certain time interval an optimized gin still creates 100 liters or 100 gallons of gas vs. your set-up producing 60 liters or 60 gallons in that same time interval. Comparing the i500 to your set-up here. If we divide 100 by 16 the outcome is a relative speed inside my column of 6.25. When we divide 60 by 2.55 square inch, the vapor speed in your column is 23.5. That is 3.7 times faster. The gasses in your set-up travel way too fast. Why is that important?
It is important because higher vapor speeds suck up higher boiling point associated rooty, nutty, earthy flavors, earlier in the run. Basically, via the small diameter riser, you over-harvest back-end flavors. And that while making gin, which is mostly a forward cut product (flowers, fruity). Your problem increases because of your high altitude. Low air pressure results in higher vapor speeds. Given where you are at, another boost of around 40%. In my system, we measure air pressure and automatically adapt cut points and/or power settings. Lowering the power setting on your set-up would not work, because it would result in higher total run times, with more potential of over-cooking the botanicals, creating more of the back-end flavors you are looking to get rid of. What I would do if I found myself in your situation is easy, and I am pretty sure SD can help you out here: get rid of the reducer and install a riser (and bridge and cooler) that are much wider in diameter. 4 inch or 5 inch would cut it.
Then do another run, taste as you go along. The back-end/tails-associated flavors will come over much later. You’ll know by tasting. If you taste what comes out and it is as if all of a sudden the music has stopped, that’s the moment where – again – tails-associated flavors come over, and where you need to stop.
A long post, but I hope you like the effort of me helping you solve your issues.
The two inch diameter riser, to the left, is too small …