HELP - Short Path Conundrum

Hello All !
So I have been a long time reader of this forum and have learned a lot. I have been doing extractions and short path distillation for roughly 1.5 years. conceptually I understand all the scientific principles we are applying in this process , but I am running into an odd issue and hopefully someone out there can help.

My issue is that our distillate test scores have dropped and I am having trouble bringing them back up. Historically , I would produce main body around 88-90% THC with total cannabanoids in the low 90% range.
Now , we are producing main body in the low to mid 80% range with cannabanoids in the high 80%. More puzzling is the fact that our Tails tests scores have routinely had higher thc and cannabanoid percentage results than the main body. Some of the runs have had crude going in at about 80% THC and the main body wouldn’t be much higher, maybe a few percentage points, but the tails would still be higher than main body. I was wondering if anyone out there has experienced this issue or if there are any theories as to what may be happening ??
Happy to answer any and all questions !

When are you switching your head, main, and tails flask?

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perhaps you are not fully devolatilizing your heads, and some terps and other junk are ending up in your main body. try letting the system dwell for a few hours longer at your heads temp range before you pop the main body and see if it brings up your score.

has there been any other changes in your method prior to distillation? ie filtration, winterization, LLE etc etc

whats your vacuum depths like from run to run? consistent?


My first assumption is isomerization
Of some kind
Changed any product brand
Solvent or powder any thing diffrent than before ?


The heads flask stays on until we reach a vapor temperature around 180/190°C. I have tried a SOP style procedure for the short path, but running multiple runs with the exact same temperature ramping , spin, and collection sizes yielded wildly different test results so I have gone back to the “ art of short path” where my determining factor for the end of heads is not just vapor temp, but seeing the reflux from heads disappear and the vapor temp rise , let a little main body run to be sure it’s cleared out then put the main body on. Main body runs at 220 mantle temp and vapor temp around 205 and usually holds constant. Main body collections have been smaller in an attempt to raise test scores , but clearly haven’t been working. I run a 2L short path with ~1400 ml crude loaded for the run. Main body will be about 500-600 ml and tails ~400 ml

Do you switch heads mains and tails on visuals ? Or on temp probe /vac

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I elaborated more on my other response above , but it’s a combination of visual indicators and vapor temp. Unfortunately I do not have a vacuum gauge currently hooked up. I switch from heads once I see the reflux stop and the vapor temp rise above 180/190° C. I’ll let a small amount of main body run, maybe 10-20ml, just to be sure all of the heads are cleared out before I begin collecting main body

how quickly are you ramping up temps?

also grab yourself a bullseye when you get the chance, best $600 youll ever spend


Well then almost sure a leak in your vapor parh is isomerizing
See higher levels of cbc in your coa s?


Whats your que for tails color of distillate ?

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Roughly 50-60 minutes after beginning my short path I’ll switch to main body.

Here are some really odd trends in the test results. CBC will be present in the crude, almost non-existent in mainbody ( usually <LOQ ) , and none detected in tails. THCV and CBD concentrations Decrease from main to tails (usually none detected by tails). CBN and CBG concentrations rise from main body to tails also. CBN obviously from the thermal degradation.

Lost on this one
What are the ratio s diffrances that are diffrent compared to your crude
Wich cananinoids you lose and wich increase compared to crude ratio wise ?
Damn mirical you did so well so long :grin:

Super simple suggestion, but have you tried utilizing another lab for analytics? Or reached out to your testing lab and spoken with their Manager/Director to discuss if they have recently switched their standards provider?

Just a thought, instead of beating yourself up on your hard earned skills first, try to reach out to them and see, hopefully it’s that simple. It’s happened to me before.

Best of luck!

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if the cannabinoids are higher in your tails than your mains, you clearly stopped early (those are not your tails!)

If you’re stopping based on mantle temp, then you have a new leak, which is changing there your mains/tails transition is. (also your heads/mains, so you’re contaminating your mains with heads and lowering potency).

@RockSteady has it right. get a gauge.

@TrueScience is also on point, although in this case it’s probably not the labs fault.

Edit: if following the same parameters multiple times gave you results all over the map, a leak seems like an even better fit to that data (given no gauge).


In my experience, on first pass, the end of main body is the most potent portion of the run because of heads fully clearing. On second pass it reverses and the tail end of mains is the least potent portion due to degradation.

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@cyclopath has a valid point and I appreciate him pointing that out. Something that wouldn’t really make sense in your case. It’s great getting to have an open forum like this, I love it.

You might also look into the use over time of the pump and the chance that you may be experiencing loss from wear and tear.

A great lesson I learned a few years ago from a engineering friend of mine, involved the loss of “ultimate” vacuum in some pumps we were running. We had recently moved our lab from seal level to over 4500 ft. due to such a massive elevation changes we had in moving to a new lab site my pumps and distillations were no longer running as expected. You will lose 2 inches of vac per 1000 feet in elevation @Tynstein. Get a gauge and try checking out those insides. Sometimes its as simple as a gasket or o-ring.

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Has the volume of crude you charge your bf with changed? I notice higher volume charges have higher vapor temp levels to get to mains/tails than lower volume charges. In my 2L rig, if I load 500ml my mains start at 158c (28 microns). But if it’s loaded with 900ml of crude, my mains will pop around high 160’s, low 170’s. I typically go by visuals with the head temp as a rough guide. Once I start getting a steady stream with a coil, I know It’s almost time to switch over to mains. Then the stream will start dripping again, and I’ll switch. Given, this is with a condenser at 92c and a cow style receiver, so YMMV.

Edit: Vac levels are important as well. They’ll start dropping once mains start to pop. As for tails, I find that a low volume BF charge will cause significant smearing. What I thought were my tails from head temp readings often end up being as strong as my mains. Even more potent than my mains if I shut the run down early. I don’t have too many data points to confirm this pattern, so I usually just try to avoid low volume bf charges.


Do you mind elaborating more on this part? I’ve always switched from heads to main when the distillate starts getting thick, stringy, and coils. But my numbers are not where I want them and my disty always has a smell, so I figure I’m having heads contamination. I’ve never noticed the distillate go back to dripping (rather than coiling) after it initially starts coiling unless I take a heat gun to the condenser or something.

I’m not sure how to use vacuum depth to indicate when to swap so I rely on vapor temp and how distillates consistency. So for you, you will see disty coiling at the end of heads - presumably this is cannabinoids? And you don’t switch until it starts dripping again? Is the change from coiling back to dripping just a function of more distillate vaporizing and condensing causing the stream to heat up causing the distillate to get hot enough to drip again rather than coil?