Pot still head configuration with alambic onion
Posted: Wed Apr 30, 2025 6:17 am
Hiya distillers.
Modular stills have a great advantage with that they allow the distiller to change the configuration of the still depending on needs and whims. The column can easily be made taller or shorter, coldfingers and reflux condensers can be fitted or removed, plates and bubblers can be added. etc. with the use of tri clamp connections. The still can grow with the owner's ambitions and love for the hobby. The fact that I could from one run to another switch from pot still to reflux still by exchanging one or two modules is why I decided to buy one of these stills. For anyone looking for a still, to buy or build, this type is the one I recommend. I am writing this because the content of this thread is based around having the luxury of a modular still.
Copper pot still head expansion chambers, so called onion heads or copper helmets, are classic features in old style pot stills. There are different views on how much added value they provide compared with a column riser in pot still mode, but they do increase the vapor to copper interaction thus "cleaning up" the alcohol somewhat and they provide some passive reflux refining the vapors exiting the onion/helmet, raising the ABV of the ethanol coming out of the PC somewhat. I am not proposing that onion heads will make a huge difference in pot still mode but they will make some difference and they look absolutely fantastic. It's the classic look of a pot still/alambique/alambic and I have always had the ambition to get me one for my still.
Last week my copper onion head arrived and I have spent the last days cleaning it, running the vinegar, steam and sacrificial runs. Now I am ready for the fun part: including it in my rig. With several modules available to me, I can chose between different configurations. There are two that I especially are looking at and I wanted to bounce these, plus one more, with you to hear your thoughts about them.
This has been my current set up in Pot Still mode. A 15cm (6") 4-to-2 inch reducer (missing in the picture), connected to a 45cm (18") long 2" copper spool and then the elbow to the PC. Its' total height is 70cm (27.5") from boiler to top of elbow. The copper spool is the only module in my set up that is made from copper.
The copper onion head is 30cm x 30cm in size with a volume of 12L, connected via 4" tri clamp ferrules on each side. I've also added a 4" spool of 15cm (6") to connect the boiler with the onion.
Here are my thoughts how to configure the pot still head.
1. My first choice is a "swan's neck" configuration: the 15cm 4-to-2 inch reducer connecting the onion with the elbow that goes to the PC. Overall height from boiler to elbow is 70cm (27.5"), the same as in my current set up. This config should work well both for stripping runs as well as spirit runs. I am expecting a lot of flavors to be passed over but the onion head in tandem with careful control of the heat source will help in separation of the fractions during the spirit run, especially in the first half of the distillation.
2. My second choice is a "long neck" configuration, a wee bit inspired by my Scottish ancestors' whisky pot stills: the 15cm 4-to-2 inch reducer connecting to the 45cm (18") copper column before the elbow to the PC. All in all a height of 115cm (45") from boiler to elbow. To be honest I am not expecting a huge difference from the first configuration and I am only thinking of using it when running spirit runs. When running slow in a spirit run I could perhaps get a tad more passive reflux and higher proof compared to the no.1 config. I am thinking this could be a set up to use for Rums and Whiskeys where I want a slightly "lighter" flavor profile. However, maybe the biggest benefit of this configuration will be the added copper contact to the vapors? The disadvantage is that the tower gets so tall and I need to stand on a chair to mount the top modules...
What do you guys think? Am I overthinking it (again)? I am not taking it so serious myself either but I would like to hear your feedback.
On top of that, I am toying with two more ideas. As I'm not entirely sure what to expect in terms of separation vs smearing, and I do know the smearing increases with stills using onions as the distillation goes on (because the passive reflux is getting less and less efficient as the dome gets hotter), I have been thinking of adding my reflux condenser to the "swan's neck" to help cool the head down a little. Not going full reflux, more like how some of the Scottish Whisky stills have neck cooling to slow the vapor flow a bit.
I've also thought just having a short stub neck, dropping the reducer altogether, and lead the vapors straight to the PC. This would primarily be a configuration for stripping runs. But I learned from Alan Bishop that having too small of an outlet from the expansion chamber could put too much pressure on the top of the onion, ultimately breaking it. In my case, I'm more concerned the center of gravity get's out of whack and the whole thing looks like it could tip over any second.
There you have it. Options are fun challenges. I am running a spirit run tomorrow for my wheated Bourbon and I am thinking of baptizing the onion with it, using the first, swan's neck configuration. Wish me luck!
Modular stills have a great advantage with that they allow the distiller to change the configuration of the still depending on needs and whims. The column can easily be made taller or shorter, coldfingers and reflux condensers can be fitted or removed, plates and bubblers can be added. etc. with the use of tri clamp connections. The still can grow with the owner's ambitions and love for the hobby. The fact that I could from one run to another switch from pot still to reflux still by exchanging one or two modules is why I decided to buy one of these stills. For anyone looking for a still, to buy or build, this type is the one I recommend. I am writing this because the content of this thread is based around having the luxury of a modular still.
Copper pot still head expansion chambers, so called onion heads or copper helmets, are classic features in old style pot stills. There are different views on how much added value they provide compared with a column riser in pot still mode, but they do increase the vapor to copper interaction thus "cleaning up" the alcohol somewhat and they provide some passive reflux refining the vapors exiting the onion/helmet, raising the ABV of the ethanol coming out of the PC somewhat. I am not proposing that onion heads will make a huge difference in pot still mode but they will make some difference and they look absolutely fantastic. It's the classic look of a pot still/alambique/alambic and I have always had the ambition to get me one for my still.
Last week my copper onion head arrived and I have spent the last days cleaning it, running the vinegar, steam and sacrificial runs. Now I am ready for the fun part: including it in my rig. With several modules available to me, I can chose between different configurations. There are two that I especially are looking at and I wanted to bounce these, plus one more, with you to hear your thoughts about them.
This has been my current set up in Pot Still mode. A 15cm (6") 4-to-2 inch reducer (missing in the picture), connected to a 45cm (18") long 2" copper spool and then the elbow to the PC. Its' total height is 70cm (27.5") from boiler to top of elbow. The copper spool is the only module in my set up that is made from copper.
The copper onion head is 30cm x 30cm in size with a volume of 12L, connected via 4" tri clamp ferrules on each side. I've also added a 4" spool of 15cm (6") to connect the boiler with the onion.
Here are my thoughts how to configure the pot still head.
1. My first choice is a "swan's neck" configuration: the 15cm 4-to-2 inch reducer connecting the onion with the elbow that goes to the PC. Overall height from boiler to elbow is 70cm (27.5"), the same as in my current set up. This config should work well both for stripping runs as well as spirit runs. I am expecting a lot of flavors to be passed over but the onion head in tandem with careful control of the heat source will help in separation of the fractions during the spirit run, especially in the first half of the distillation.
2. My second choice is a "long neck" configuration, a wee bit inspired by my Scottish ancestors' whisky pot stills: the 15cm 4-to-2 inch reducer connecting to the 45cm (18") copper column before the elbow to the PC. All in all a height of 115cm (45") from boiler to elbow. To be honest I am not expecting a huge difference from the first configuration and I am only thinking of using it when running spirit runs. When running slow in a spirit run I could perhaps get a tad more passive reflux and higher proof compared to the no.1 config. I am thinking this could be a set up to use for Rums and Whiskeys where I want a slightly "lighter" flavor profile. However, maybe the biggest benefit of this configuration will be the added copper contact to the vapors? The disadvantage is that the tower gets so tall and I need to stand on a chair to mount the top modules...
What do you guys think? Am I overthinking it (again)? I am not taking it so serious myself either but I would like to hear your feedback.
On top of that, I am toying with two more ideas. As I'm not entirely sure what to expect in terms of separation vs smearing, and I do know the smearing increases with stills using onions as the distillation goes on (because the passive reflux is getting less and less efficient as the dome gets hotter), I have been thinking of adding my reflux condenser to the "swan's neck" to help cool the head down a little. Not going full reflux, more like how some of the Scottish Whisky stills have neck cooling to slow the vapor flow a bit.
I've also thought just having a short stub neck, dropping the reducer altogether, and lead the vapors straight to the PC. This would primarily be a configuration for stripping runs. But I learned from Alan Bishop that having too small of an outlet from the expansion chamber could put too much pressure on the top of the onion, ultimately breaking it. In my case, I'm more concerned the center of gravity get's out of whack and the whole thing looks like it could tip over any second.
There you have it. Options are fun challenges. I am running a spirit run tomorrow for my wheated Bourbon and I am thinking of baptizing the onion with it, using the first, swan's neck configuration. Wish me luck!
It doesn't foam on a spirit run 
Should I be running around with my hands waving in the air in panic - 1,5cl trapped in a pool under the level line of the spigot? 