Have any Questions?


Jun 08, 2022 View:

Dephlegmator and Condenser Equilibrium

Yesterday we fired up our still for the first time (200gal of 9.5% fermented agave) and went to work. For nearly 5 hours the kettle temp (182F), the dephlegmator temp (164.8F) and the condenser temp (162.5F) all held constant. Then out of no where a weird thing started happening. The still temp rose to 190F and then held there. When that happened our dephlegmator and condenser started to do this dance where the temp on the condenser would go up to 170F, but the dephlegmator temp would be in the mid 160s. THen the condensor temp would start to fall and the dephlegmator temp would rise. This continued until we stopped operation for the evening, about 2 hours. Any one have an idea as to why? We made no adjustments to anything when this started...soon as we noticed it we tried adjusting input and output on the dephlegmator to try and get the temps to settle, this just made the swings worse. After about an hour of messing with it, we put everything back to where it was and this little rhythm started and was very predictible, just not what we thought was supposed to happen.

We have a pot still with 4 plate column on a stand next to the still, and then condenser next to that, all in line. This is our first time using a column and dephlegmator so we are sure we may not be controlling it correctly. We assumed that once we set everything so that we were getting a constant flow and stable temps, that it would work like a pot still, where the temp gradually increases and the proof decreases over time, without any adjustments to heat or cooling (this is what all our previous experiences with a pot still were like). Any feedback or insights would be greatly appreciated.

Oh yeah, we are 100% manual control now. No automation at all.


The kettle temp should slowly increase as the abv drops.  I usually start about 185-190 and slowly increase to 200 as the boiler becomes depleted.  Can't help you on the deflag as I don't run one, I run a vm still head.   the abv will slowly drop if I don't make any changes to reflux rate.  

I would guess the surging might be from the column not draining all the way back to the kettle?  I assume there is a drain from the column back to the kettle.   I would start looking in that area.  

I am at 6000ft, so water bp is about 200.  

Reply:35 minutes ago, Storm King Distilling Co. said:

With a large charge, we can easily keep our still at the same temperature for several hours on a heavily refluxed GNS/vodka run, in part because our thermometer is in the headspace of the kettle. This is visually looking at an analogue thermometer - not the same as actual temperature changes since small increments are difficult to observe.

Are you flooding one or more of your plates? What you are describing would match up with a plate being flooded then clearing, releasing a bolus of gas which would raise your condensor temp which would  cool again if the plate flooded again and so forth.



Attached are a pic of our setup and our current reflux (nothing looks flooded). You can see the digital thermometers on top of the dephlegmator and the top of the condenser (this is basically the vapor temp after making two turns out of the dephlegmator). The two temps are currently 30 degrees different. Again, yesterday for most of our run they were within a few degrees of each other and we were collecting about 1qt every 2.5mins at 70-80% abv. The kettle temp was reading an analog thermometer and it was roughly 82-85 for a long time. We collected roughly 27 gallons.


Also, all day today the alcohol coming out of the parrot has been doing so in fairly big bursts with little temperature changes on dephlegmator and top of the condenser. The still is staying constant at around 192F and everything looks normal inside. No pressure buildup in the system that we can see or tell.


When you say big bursts, do you mean that you are getting pressure surges that make your hydrometer jump?


Yeah, the hydrometer will bounce around a lot then can feel air pushing through the vents that our parrot has when this happens. One thing we just thought of is that our charge in the still was not large enough. We had to ferment in our still for our first batch because our pump has been delayed, we went a little low to make sure we didn't have any of the ferment bubble up into the helmet. So the still is a 1000L and we made a batch of 200gal, so we are about 65 gallons short.

Also, the last time we turned the water on and restricted flow out on the condenser (putting pressure on the water inside) our proof dropped to near 0. We suspect there is a pinhole leak in the condenser (not sure how that would create two temps that are 30 degrees off from each other and only 4ft apart). If there is a leak it is extremely small because there is no apparent drop in proof if water is in the condenser, but without pressure.


I would like to do a conference call with you and my Master Distiller.  There will be no charge for our help.  What would be a good time for us to call you on Monday?  You can email me privately [email protected]



I have a possible explanation.

If your pot temperature is 182f that indicates your ABV in your pot is close to 50%abv but you said 9.5%  (see graphs of boiling point vs. ABV at sea level)

 If the temperature sensor in the pot is above the liquid I have observed that it reads lower than if it is submerged.

As your run progressed you have a higher % of solids and there may have been a buildup of foam that eventually reaches the temperature sensor and suddenly your temperature reading goes up because the foam temperature will be close to the liquid temperature.

Regarding a possible leak in your condenser the symptoms you gave make that very likely. If your condenser water is exiting the pipework to a drain well below the condenser then there will be a slight vacuum in the condenser. A hole in the coil/jacket will "suck" some of your alcohol vapor or condensate into the cooling water and you wouldn't notice anything except low yield. As you applied back pressure on the condenser water it would push cooling water into the alcohol side and your ABV drops as observed. Easy to check with cooling water on and still switched off.


the poster is about 5800 ft, so that will drop the boiling points.  I am at 6k and 185 is not uncommon for a starting boiler temp for a 10% wash.   Same with head temps, 140 proof is about 182 deg.  


That pretty well kills my theory then. I didn't see any mention of  altitude and that is why I mentioned sea level for the common boiling point curves


Couple things to check.

Calibrate all your thermometers, together, and verify they are all working correctly.  You've mentioned enough quirky things about temperature to warrant a check.  Jiggle them/tap them/shake them when confirming to verify there is nothing odd.  When you replace them, do not put them back in the same positions, note what came from where, and where you put it (unless there is some reason you can't do this). 

Verify your steam pressure is solid, wavering steam pressure can very easily create variable output rates, and impact vapor temps.  If your boiler cut-in/cut-out is wide, it's going to drive you nuts, on a faster run.  Likewise, steam trap issues can also be a big gremlin.

Verify your water pressure/flow rates are not varying through the run, varying flow rates will also cause variable output rates, dips, jumps.  When flow rate to the reflux/dephlegmator drops, it's very common to see a jump in flow.  We've heard lots of funny stories about toilet flushes causing problems, running water in other parts of the distillery (hoses, wash down) reducing flow rates and impacting the still.  During your run, you'll probably be sitting around 1psi, give or take.

Check for that leak in the condenser.  Proof falling to zero is very very odd unless you are dumping water.  Just test this with the still not full or not running.  Turn the condenser water up, restrict output, and check to see if you are dripping from the dephleg or out the parrot (just take the parrot off).



Guys, confirmed likely pin hole leak in the condenser, only leaves water when under pressure. Have a call in to Still dragon to provide a fix. As for our boiler, I will take a look and report but I believe we have our high fire coming on only if it gets below 2psi and then we have the actual cut off at 7or8psi +/- 2psi. Our internal kettle temp is about 10 inches of the bottom so no issue with that temp. The digital thermometers read 64 and 65 (one is about a foot higher than the other) under normal day time conditions, which is about the air temp in the distillery.

The werid thing for us was that we had everything dialed in and 160proof juice was flowing for 4 hours, and then everything started going up and down. 

What we think happened was that because we left the flow through the dephlegmator untouched was that we sucked all easy ethanol out and then when the bouncing started it was because the still was working so hard to produce enough ethanol that it would build it up then finally release it in a surge.

Yesterday when we went to finish the run it was doing this surge thing for.a.few hours then went from 90 proof to straight up tails at 20 proof in no time.


Thank you all for your input, and thank you Paul for taking the time to give me a call. I spoke with Stilldragon as well on Monday and based on volume and the stats I provided we came to the conclusion that the amount of alcohol I collected would be about right, at 160 proof. Basically we were running the dephlegmator without changing the temp so the still was working hard for 4 hours pumping and collecting very high proof spirits and then all the weird stuff started happening because there wasn't much alcohol remaining. Having never run a dephlegmator before I guess I was expecting the temp to gradually change on its own and didn't realize that if we don't reduce water input or decrease outflow, then we can keep that proof coming out very high. Next time we will keep it at that same temp to make the heads cut then increase a little bit because I am not sure that the Agave spirit should be 160. Also, the tails cut was hard to make with everything coming out that high, should be easier if we lower the proof a bit (it went from tasting awesome to 10% and oily in a few seconds, so want to avoid the drastic shift). StillDragon is also sending us a new condenser so props to them for excellent customer service.


You should see the boiler temp change as the alcohol is depleted.  That will be a good sign that you are getting to the end of the run.   I will start about 185 and end up at 200.  I am close in altitude so you should get similar numbers.  


Bluefish, exactly. When we went back and looked at the data that we collected, prior to panicking, we had very minor increases in internal kettle temp, then it made a visible jump to roughly 192, then climbed. We suspect that that jump would have been a good "tails" signal. Unfortunately we didn't make that tight cut, but overall flavor seems really good still, so maybe we are ok.

Reply:On Saturday, February 24, 2018 at 2:50 PM, Storm King Distilling Co. said:

@Storm King Distilling Co. Thanks for posting the solution after you figured it out. Did the same thing yesterday. Ran too much water to the deph while pulling hearts. Towards the end of the hearts cut the plates would all stack and then a flood of distillate would come out, and the plates would unstack.  Then repeat again. My finished hearts cut ended up being 180 proof running through 5 plates, when it usually ends up being around 165 proof. I also have a pinhole leak in my condenser. Sounds like we have a lot of common problems. Learning something every day.