When do you decarb?

Hi all, short time lurker, first time poster. Just wanted to thank you all for letting me be a part of your fine forum. Now that that’s out of the way:

When you’re doing a run of distillates, it seems like it’s possible for ethanol to decarb cannabis on its own, and there are people doing decarb at various stages, including in the rotovap itself. I’m planning on doing chilled ethanol extraction, taking that extract and running it in a rotovap, and then chucking it in a hot plate as needed for any residuals (although canada’s residual solvent limit is currently 5000 ppm, I imagine the industry standard is far lower, so I would want to keep it down as low as possible while still performing in a cart).

So if you’re just planning on extracting thc with chilled ethanol, running it in a roto, and tossing it in a hot plate as necessary, is there any particular point in the process where it should be decarboxylated? Is that something that happens along the way? What are the advantages of doing it pre-extraction? in the rotovap? in the hot plate?

OT: After this sort of process, is there any way to reclaim your ethanol afterwards? I have been reading that aziotropes make it difficult to take the terpenes themselves out of the ethanol with this sort of extraction, but even if I were to reclaim most of them, I would imagine the extraction capacity of my ethanol would still be reduced. am I wrong in saying that I should be using fresh ethanol for nearly every extraction? And that I will be losing a lot of goodies this way? If one wanted to do full strain profiles in an extract, is it best to go with initial CO2 extraction so you can easily get your terps?

Thank you for your insight.

EDIT: Ethanol Azeotropes - Attn: EtOH cannabis extractors!
Reading for me or anybody like me.

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You can and should re use your ethanol after extractions. If you are not using heptane denatured ethanol you can check the purity of the recycled ethanol with a hydrometer and decide when you want to toss it (use it for cleaning, etc.) or purify it.

You’ll recover most of your ethanol on the rotovap.

If you are going to make distillate you should decarb before running it thru the short path. An easy way is to evap as much ethanol as you can on the rotovap, then transfer to a glass or steel container with at least 2x the volume of oil that you have, and decarb that on a hot plate with stirring at 140C for an hour or so or until you stop seeing bubbles. Place some spatulas in the vessel to create more surface area to help the bubble/foam layer pop so that it is less likely to overflow.

You can also decarb in the rotovap, but you should then use something with an appropriate boiling point in the bath.

I’ll help you out with any other questions to the best I can, but pretty much anything you can possibly ask has been answered on here if you use the search bar. Welcome to the forum!


So no plan on distillation?

Adding terpenes back?

Pardon me if Im misinformed because Ive been under the impression that a rotovap was the distillation apparatus in that case. is the rotovap not doing as much work as I expect? I’d love to add my terpenes back but Im not sure about getting them into a re-addable state after doing a QWET.

I’ll be using nondenatured 190 proof at least, so this is good news. You wouldn’t happen to have any resources regarding some sort of critical threshold when the ethanol less appropriate for reuse? EDIT: I will probably figure this out on my own, as long as I know that purifying it is more or less a trivial process

Thank you for this. Like I mentioned to cyclopath, I was under the impression the rotovap procedure acted as distillation, but clearly it seems like I’m misinformed. So after the rotovap and hot plate decarb, there’s then another step in a short path?

I’ll help you out with any other questions to the best I can, but pretty much anything you can possibly ask has been answered on here if you use the search bar. Welcome to the forum!

Thank you kindly, sometimes it’s difficult to answer specific questions, so I end up with things like the question in the OP; if there’s some general FAQ or other megathread type resource where I can find answers to dumb questions, I would love a link. Otherwise, I will just dig as well as I can.

From my last experience decarbing post wash, the heating created lots of brown gunk. I am presuming that is what is removed via spd?

For the spd less folk like me, decarbing pre wash seems make much better tasting oil. The gunk that forms during post wash decarbing is not easy to filter out at my low tech levels. But just a guess, decarbing biomass in an oven is not 100% and there is cbda in the extract, which I don’t think is exactly a bad thing, but it makes you fall short on the efficiency of your extraction.

I have never used anything but heptane denatured. With that I’ve never taken any out of commission. I just keep using it and topping it off. So far no noticeable yield decreases.

But get yourself a hydrometer and measure the proof of the solvent as you go. When it gets below 160 proof, I might start worrying about it affecting yield. Not sure tho.

Yeah to make distillate, you extract, evaporate solvent, decarb oil, and then distill under vacuum (short path distillation). Whether or not you do that depends on what you want your end product to be. For example shatter is not distilled, nor is EHO (ethanol hash oil) which is possible to use in carts, though a bit trickier than distillate alone.

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No, a rotovap is not a distillation apparatus. You will need to look at short path distillation equipment if that is your goal.

Well that’s nice, now I feel like a dumbass. But it’s okay! So, can I actually even make a vapeable end product just with the hot plate and the rotovap? What’s the major advantage of doing the distillation afterwards?


The only stupid question is one you needed to ask in order to understand, and didn’t ask because you didn’t wanna sound stupid.

You can still make a cartridge, but it’s more difficult, especially if you didn’t winterize. It won’t be near the potency of a distilled product

It’s a common misconception because people refer to reclaiming their solvent as “distilling” from the oil. You get your solvent (etoh in your case) back, and you’re left with your crude oil.

The plan is absolutely to winterize, or at least, to do the extraction at dry ice temperatures and see what effect winterizing has. From what I’ve read, doing the extraction at those temperatures leaves it pretty clean from waxes and such.


This makes sense, the distilled part is what you collect, so the rotavap definitely wouldn’t distill the crude, just the ethanol. rotovap is still distillation equipment, but not for what I’m trying to distill.


So you’re going to chill the alcohol to -78c and then do the extraction? Followed by filtration?

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That’s the plan, yeah. Then the filtrate would ideally be good to go into the roto if I didn’t need to do anything else with it beforehand.

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Yep. That is not winterization, but may well get you to an almost cart ready crude.

If going that route you might Decarb under pressure to retain terps?


It is a distillation apparatus, but as you’re now aware, not for distilling your cannabinoids, or making the product known in the cannabis trade as “distillate”.

If you need terps, because you cooked yours off on a hot plate, then you have to purchase them. Sources for those can be found here too.

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I guess winterization is specifically when you let an ethanol extract sit at temperature to let your impurities precipitate out? doing a filtration right after a cold extraction would be a shortcut to that process? if I’m off base here let me know. And I’m going to check out the link here. i can’t speak your guys’ praises enough. thank you all for your help.

If you extract cold you don’t pick up much in the way of waxes. If you concentrate that primary extraction, then get it even colder, you might drop some fats and waxes that you can filter out.

Right now you are simply filtering out the plant matter (particulates).

Check out the bucket tek thread & get yourself a panda with a sock in it.