lots of output all at once followed by temperature spike

[RumRaider]

Hi,
I can't find the answer to this anywhere else and am hoping someone can help.

I was running a 4 Gallon fruit based wash through a brewhaus 8 gallon reflux still (on full reflux, hooked up per manufacturers instructions). I had just cleaned it by rinsing and then distilling a few gallons of water through it. Things were progressing as usual (this was only my 4th run overall so "as usual" is a relative term). I was getting 1 drop to several drops of foreshots per second and temp reading was stable around 178F. After a few minutes i realized the rate of drops was fine but the drops were smaller in size than usual and it was taking a long time to collect a small amount of output. I turned the heat up very slightly thinking it might speed things up a bit. The temp went up to 184F but the output went ballistic! Immediately the output was a steady and FULL stream and the jar filled up FAST, the still just burped out distillate at an incredible rate (it started with maybe 3OZ in the jar and finished at about a full pint in just two big burps) and then went back to normal. I quickly changed jars and went back to 178F and a more normal output. I figured "fine, i learned a small temp change can have big results" and pressed on. Then it happened again several times without me doing anything. The temp would slowly drop to as low as 169F, there would be a big surge (burp is the best term i can come up with) in output, followed within 1 second by a temp run up which would peak at about 181F. Then it would return to normal (174-178F and one to a few drops per second) for awhile then repeat the cycle: temp decrease, big burp with temp spike and return to normal. Again, i didn't do anything to the heat after that first time, it just happened on its own several tmes. I made cuts in pint jars and when i finished i had tossed a pint of foreshots and was left with 5 1/2 pints of hearts and tails. I then tested using an alcometer and the jars were 75%, 62%, 58%, 45%, 38%, and the last 1/2 pint jumped back up to 62% (triple checked it).

My questions are:
What caused the "burping" (and is there a better term than "burping")?
My prior runs had higher %ABV (started at 92% after tossing foreshots), could the burping problem also have lowered the %ABV of my output?
How could that last 1/2 pint have gone up in percent ABV?

Any insight would be much appreciated as i'm baffled and worried that the burps are also a safety concern

[rad14701]

You're trying to control temperature instead of product flow rate... Stop it... Go back and research how to run your still properly...

[RumRaider]

You're trying to control temperature instead of product flow rate... Stop it... Go back and research how to run your still properly...

I'm trying to contol both as they are related. I've read the posts that say temp isn't important but for a beginner it is a helpful indicator. Not sure what you mean about not running my still properly, I'm running it per the instructions and what i learned here, is there more specific advice or some thread someone can point me to instead of just saying "research".

[rad14701]

Why you can't control a still with boiler temperature
Do I need a thermometer on my pot still?

[Prairiepiss]

+1 on the links Rad provided.

Now I would like to point you to the CM mod thread in my signature. Within that thread there is a mod for the cooling flow of your still. I would suggest doing this. It will give you much better control over your still.

You said you were running it as the manufacture said to. Here is something I have found about running with the cooling like they suggest. When the cooling water for your reflux condenser comes from your product condenser. It will not have a steady temp. If the heat input changes and you get more vapor flow it heats the water up going into the reflux condenser. When it gets hotter water it allows more vapor past. This vapor increases the temp even more. So again it jumps even more. I had a heck of a time trying to control my still because of this. Then I did the mod in that thread. This gives you a steady coolant input temp to both condensers. So one won't control the other. You will be controlling it. With this setup I found you could adjust either the coolant flow or the heat input. Without temps or product output running away from you.

Just so you know my still is a cm still similar to yours. I have never used a thermometer in it. So it can be done.

[RumRaider]

OK thanks, i now realize that the wash will boil when it reaches its boiling point (and every wash will have a different boiling point). And, temp is simply an "after the fact" piece of info that is not something useful to guide my distilling decisions. I also realize that flow rate is what should dictate heat input. I guess i can extrapolate that this particular wash boiled at a lower point than my previous washes and that more water was output which lowered the %ABV on this batch relative to previous batches. Perhaps the spike in %ABV on the last jar of this batch was because the "burps" were loaded with water and i didn't get a "burp" in the last jar. Is this at least the beginning of what you wanted me to figure out?

I still don't know why it "burped". That much output all at once is not something i want to repeat.

[RumRaider]

+1 on the links Rad provided.

Now I would like to point you to the CM mod thread in my signature. Within that thread there is a mod for the cooling flow of your still. I would suggest doing this. It will give you much better control over your still.

You said you were running it as the manufacture said to. Here is something I have found about running with the cooling like they suggest. When the cooling water for your reflux condenser comes from your product condenser. It will not have a steady temp. If the heat input changes and you get more vapor flow it heats the water up going into the reflux condenser. When it gets hotter water it allows more vapor past. This vapor increases the temp even more. So again it jumps even more. I had a heck of a time trying to control my still because of this. Then I did the mod in that thread. This gives you a steady coolant input temp to both condensers. So one won't control the other. You will be controlling it. With this setup I found you could adjust either the coolant flow or the heat input. Without temps or product output running away from you.

Just so you know my still is a cm still similar to yours. I have never used a thermometer in it. So it can be done.

Maybe the coolant flow is why i got the "burps". I read those links in your signature block before and the one on CM mods i've gone over several times. I've insulated the condenser and have the second water pump on hand so i can seperate the flow to the product and reflux condensers. I'll do the water re-routing on my next run. I don't have the talent or equipment to weld a replacement cap on top of the tower or to make a center ring but i've got both ideas in my head and my eyes open for some cork. Thank you, I appreciate you guys sharing your expertise!

[rad14701]

Somehow I managed to overlook the fact that this is a reflux column... In that case there are other more relevant topics which would be better than the ones I posted previously... Sorry for any confusion caused by my oversight...

[RumRaider]

Somehow I managed to overlook the fact that this is a reflux column... In that case there are other more relevant topics which would be better than the ones I posted previously... Sorry for any confusion caused by my oversight...

No sweat, i'm a bit smarter for having read those "why chasing temps doesn't work" threads.

What are the more relevant topics though?

[Prairiepiss]

Something else I forgot to mention and wanted too. It's possible that the column is packed too tight. Allowing more reflux to stand in the column. Or flooding. It could be building up to a point and then getting pushed out all at once. That would explain the sudden burp when more heat was applied.

But I would change one thing at a time. That way you know if that one thing fixed it or not. If you do more then one thing you won't really know what fixed it.

[RumRaider]

Something else I forgot to mention and wanted too. It's possible that the column is packed too tight. Allowing more reflux to stand in the column. Or flooding. It could be building up to a point and then getting pushed out all at once. That would explain the sudden burp when more heat was applied.

But I would change one thing at a time. That way you know if that one thing fixed it or not. If you do more then one thing you won't really know what fixed it.

Glad you said that. I ran across a hint of this in some other threads i read. It would make sense as i just cleaned it and was of the opinion that the packing should be rather tight. it also fits in with your earlier post about the temps in the condensers because if the packing is holding more liquid the higher heat would cause the viscious circle of heating you described and cause the burp.

[RumRaider]

Just a followup for anyone battling the same problem: it was the packing. I've made a few more runs and what works for me is 2 rolls of copper mesh (was 4). And, I roll them into a sort of cone shape rather than like a log. I put them in the column with the small ends of the cones at the bottom. I still get 89% ABV on my reflux runs and it is steady, no burping! I also feel like the cone shape helps keep the refluxed drops in the middle of the column instead of down the sides (I could be wrong about that but that's my thinkin')
Thanks to all who posted!
RR