Decarboxylation under Vacuum?

I have lots of customers asking me about decarboxylation under vacuum. They are hoping to use the low temp processing capabilities to decarb at a lower temperature. I am not familiar with using vacuum to decarb at lower temps. Am I missing something here?


People do it in rotovaps all the time. You could just as easily use a vacuum oven though.


I guess I am looking for the answer from a Chemist’s point of view. Does the reduced pressure facilitate lower temp decarb?

Yes it does. This is also why you want as low a vacuum as possible when making distillate. It helps to lower the temperature that the cannanibinoid fraction becomes a vapor.


Do we have a time/temp/vac curve on the difference?

From this paper, my read is that the vacuum doesn’t substantially affect the decarb time. There are time/temp graphs about half way through. They look not dissimilar to ones from non-vacuum processes.

I’m not a chemist, but my understanding of decarboxylation is that we’re basically dumping enough energy into the material to beak the bond between the carboxyl and the cannabinoid. I think that means that the primary determinant will be the heat energy applied to the material, not the pressure of the environment.

It’s definitely possible I’m completely wrong on this one and will be happy to be corrected by someone smarter than me on this one.


You and me both!

From my experience with it, regardless of vacuum, decarb really starts around 135C. I’ve tried a few different time/temp ratios with and without vac and pressure, seems like if I don’t hold that 135-145 for a period of time determined by the volume, then I’ll still end up with THCA.


Yeah I’ve never observed it actually speeding up the process, it just allows you to do it at a lower temperature thereby limiting thermal degradation. That’s really the point of doing things under vacuum.

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What were the conditions? My experience is with dewaxed CO2 oil using a hotplate/stirbar as well as distilling in a shortpath. On the plate the reaction is obvious by the amber-ish bubbles that come off of it, in the spd its the smell. All the way down to 250 micron I won’t get the smell until 135-145.


what youre describing is the pressure/boiling point relationship, not an influence of pressure on decarboxlyation reaction rate. You’re right about the phenomenon being a contributing driving force of vacuum/molecular distillation, but its not applicable here.

Also, since decarboxylation of cannabinoid acids is not isentropic, Le Chatelier’s principle does not apply to the reaction. Meaning, decarboxylation at a high pressure should not impede the reaction from moving forward. Likewise, I would not expect low pressure to pull the reaction forward either.


Correct, the only reason I mentioned distillation was the thermal degradation piece. I can see no other reason to decarb under vacuum except for that and even that doesn’t seem to be a big deal given the temps and times we work with at atmosphere to decarb. It isn’t something we bother with though, we’re a CO2 shop so we decarb in a forced air oven before extracting.


Decarb in positive pressure… Now we’re on to something…


Terpene retention!


My takeaway from this paper was that decarbing goes on in the rotovap whether you want it to or not because of thermal degredation and depending on what’s decarbing and at what temperature, you lose up to 50% of what you started with in the process.

Also the paper was done under vacuum so all those results are for a little to no oxygen environment.

oh, and that paper has supplemental data too that’s not in the pdf and that you can download free for additional details.

Ok so I don’t think any said why I was taught u would…

Certain things can oxidize and/or get really dark when oxygen touches it during the heating process
Will help keep lighter color and the original look more…what I was told

Hope this helps

Here is a quick study from peer reviewed literature. It is not much but nowhere are they concerned about the pressure in a study concerned with kinetics. Only time and temp and various other factors but no references to pressure itself as would be the case in a boiling temp chart.

I cannot envision how lower pressure could initiate decarboxylation the same way I can envision vacuum lowering the boiling point of a compound.


Decarbing under vac makes sense when heading to distillate. You’re essentially combining decarb with terp strip/devolitilzation.

If decarbing for edibles or to reduce the viscosity for pens, then doing it under vac is not necessary, and in the case of pens, might well be counter productive.

ie you might even want to Decarb under pressure to retain terps?