Vacuum Purging BHO

How to vacuum purge BHO?

BHO extractions are becoming more and more popular today. In this Blog, we have already seen different BHO extractors and explained their functioning and advantages and disadvantages when making marijuana oil.

In this post we will focus on how to purge the solvent from this appreciated liquid gold, which offers us new experiences and opens new horizons in the world of marijuana concentrates and their recreational and medicinal uses.

Once the BHO extraction (with purified butane gas) is done, we have to purge any remaining trace of butane present in the extract. First, we will make a light purge with a bain-marie (water bath). During this process, we can observe how a large number of bubbles are formed and then burst, releasing the gas retained. In this first purge we remove an important amount of gas from our BHO, but it is not enough to get a marijuana oil 100 % clean of impurities.

In these pictures you can see the steps followed before the vacuum purge, so you can see the state of the BHO after this first and important bleeding performed with bain-marie (water bath). Always purge the gas next to a window or directly in an open area.

BHO purge with bain-marie at 35º
BHO purge in a water bath at 35ºC

In the following picture, taken a few minutes later, we can see how almost all the gas used for the extraction has evaporated. However, the remaining resin concentrate still contains butane, so we must vacuum purge it to leave it completely free from impurities.

Foto 2 - Most of the gas is purged but the BHO even contains gas
Most of the gas has evaporated, but the BHO still contains gas

At this point, we can pop the remaining bubbles with a dabber to release the maximum amount of gas contained in the extraction.

Foto 3 - The first purge with bain-marie done with success
Bain-marie purge successfully performed

One of the easiest ways to know if the BHO still contains gas is, after the first water bath purge, taking some BHO with a dabber and approaching a flame to the oil  (Warning: do not approach any flame or spark before or during the water bath purging process, and do not approach any flame to the Pyrex tray until all gas has been purged). If we see or hear small sparks coming from our BHO, then our extract still contains gas and must necessarily be vacuum purged to ensure a final product without any trace of gas. Vacuum purging is advised by all professionals in any extraction with solvent.

More examples of gas purge of BHO in water bath

First gas purge of the BHO
First gas purge of the BHO

Bit the gas evaporates and it remains the BHO
The gas slowly evaporates

Here the gas of the BHO extraction is almost completely evaporated
The butane contained in our BHO extraction is almost completely evaporated

Bubbles releasing Gas
Bubbles releasing butane

To correctly vacuum purge our marijuana oil we need the vacuum extraction kit. Ours is composed of:

  • A Rothenberger vacuum pump
  • 2 Oil canisters for the maintenance of the vacuum pump
  • 1 Connecting pipe to connect the vacuum pump and the desiccating chamber
  • 1 Vacuum purge chamber with stopcock

Once we have all the necessary equipment ready, it's time to set it up and start vacuum purging our BHO extractions.

The vacuum compressor for the BHO purge

Rothenberger pump for the vacuum extraction
Rothenberger pump for the vacuum extraction

This is an essential element to purge out the gas from our oil, since it is the power source that will generate the air suction in the vacuum chamber.

The Rothenberger vacuum pump has a final vacuum of up to 34 bar with a pumprating of 170 L/min (6 CFM). Motor rating is 3440 RPM with two-stage rotary vane pump to get greater efficiency. Oil capacity is 330 ml.

This vacuum pump has enough power to remove all small gas bubbles trapped in the marijuana oil in a very effective and fast way.

Technical features of the Rothenberger Roairvac 1.5:

  • Weight: 11.5 Kg
  • Final Vacuum: 34bar
  • Pumprating: 170 L/min - 6CFM
  • Voltage: 230v
  • Oil Tank: 330ml
  • Motor: 2-stage rotary vane pump
  • Motor rating: 3440 rpm
  • Standard Connector SAE 1/4"
  • Compatible Connectors: 5/6" - 3/8"

Vacuum connecting pipe

Tube for the vacuum extraction of the BHO
Connecting pipe for vacuum purging BHO

This connection tube is another of the three elements necessary to perform the vacuum purge. It?s composed of a rigid body coated with a protective plastic layer. This tube features high pressure resistance during the vacuum process, without getting blocked by the suction power generated by the pump.

It?s important to emphasize that this tube must be specifically designed for the use with vacuum, otherwise it?s possible that it bends or twists without properly performing the vacuum extraction.

At both ends, we find two adapters with a screw to connect the pump with the vacuum chamber without air leaks for a rapid and effective purge.

Vacuum purging chamber with stopcock

Acrylic desiccating chamber for BHO
Acrylic vacuum chamber for BHO

This is the third indispensable element to purge our BHO. This acrylic vacuum chamber has a stopcock and great resistance to implosion. This tool is composed of two semi-spheres, being one of them the base and the other one the lid with the stopcock, which should be open to allow the vacuum process. Inside the lower, inner semi-sphere, we find a support plate where we have to place the BHO that we want to purge.

How to vacuum purge a BHO extraction

We have all the necessary equipment to purge the BHO that we have obtained with an extractor, an unbleached coffee filter, gas free of impurities and of course, the high grade raw material: buds full of large resin glands.

The first step is to connect the required equipment. The ideal is taking advantage of the liquid state of the BHO after the first purge - performed with bain-marie - to ease the removal of the gas bubbles that are trapped inside the oil. The more solid the oil, the harder will be to remove the impurities contained in the concentrated cannabis resin.

Gathering the BHO with a spatula
Collecting the BHO with a spatula

Foto 12 - BHO before the vacuum purge
BHO before the vacuum purge

We recommend using low temperatures - around 35ºC - for the first purge (water bath) to remove the maximum possible amount of butane without affecting the organoleptic properties of the oil, since aromatic terpenes evaporate faster as temperatures rise.

Once all devices are ready to use, put the BHO on a baking paper or silicone pad inside the vacuum chamber. Now, and after checking that all components are correctly connected, we can turn on the vacuum pump.

The pointer of the barometer will always mark the pressure inside the vacuum chamber; when it reaches zero, the vacuum is created and the BHO starts purging.

The BHO purging in the desiccator chamber
BHO purging inside the vacuum chamber

After reaching the vacuum phase we can see almost immediately how the oil slowly transforms its appearance, developing craters caused by the emergence of bubbles created from the pressure of the compressor. These bubbles will burst and crystallize simultaneously during all the vacuum process taking form of a crystallized sponge, with an exponential increase of its volume.

At the time that we stop the vacuum we can observe how the appearance of crystallized sponge decreases and returns to its initial state, but being less fluid than before starting to purge.

We should repeat this process approximately 4 times (or more) for about 10 to 20 minutes, always remembering that this period of time can vary depending on different factors, such as the amount of butane present in the BHO after the first water bath, the amount of BHO to purge or the room temperature (the lower the temperature, the more difficult to remove the bubbles).

As we have no way to know the exact period of time required to completely remove all butane, we must use as reference the BHO itself. When its appearance doesn?t change at all and it stays in the form of a crystallized sponge even under vacuum, we have successfully performed the purging process and we can proceed to consume or store our oil.

BHO after the vacuum extraction
BHO after the vacuum process

The BHO obtained can have different shapes and textures. If it looks like a compacted volcanic rock we can save it as is because it doesn?t contain humidity and can be stored for a long time. On the other hand, if it remains in the form of a crystallized sponge, we can compact it and give it a round shape to store it easier in nontoxic and non-adherent silicone containers or in an essence jar with protection against UVA rays, so it can be consumed when you want.

Compacted BHO after the vacuum purge
Compacted BHO after the vacuum purge

BHO without gas remains
BHO without butane traces

Other samples and forms of BHO

BHO according to their type
Different strains/techniques produce different types of BHO

It is important to highlight and remember that during a BHO extractions we are using butane gas, and we must be extremely careful when we deal with any volatile product that can be set on fire with a simple spark produced by a lighter, by the brushing of one metal with another metal, by heat sources, electronic devices, certain types of clothes, etc.

Remember that performing these extractions in an open place, preventing any butane accumulation, is absolutely essential. We also want you to remember that gas is heavier than air, so it will always stay below air and can settle on the floor if you don?t take the above mentioned precautions. You should always avoid basements since that the gas can be accumulated and explode.

So, if you enjoy making and using your BHO, always take extreme care during the process !

The articles published by Alchimiaweb, S.L. are reserved for adult clients only. We would like to remind our customers that cannabis seeds are not listed in the European Community catalogue. They are products intended for genetic conservation and collecting, in no case for cultivation. In some countries it is strictly forbidden to germinate cannabis seeds, other than those authorised by the European Union. We recommend our customers not to infringe the law in any way, we are not responsible for their use.

Comments in “Vacuum Purging BHO” (7)


Killer keithILGM Is an Alchimia client 2021-09-13
Folks seems as usual you seem to be in a hurry. You cannot bake a cake for ten minutes if you want it to be right. Same with our beloved "liquid gold"....extraction directly into my Pyrex round pie dish, pie dish goes directly into my "Slick-Vac-Seal" brand vac chamber, set my heat plate at 129degrees. (Remember the heat has to transfer through the floor of vac chamber,and, the thickness of the Pyrex dish, also start heat plate 45min. -1hrs. beforehand). NO MATTER WHAT I DO NOT PLAY WITH THE PRODUCT IN AND OUT OF PARCHMENT....why not just purge? I purge all my concentrate NO LESS THAN 24hrs. MINIMUM no question. Usually I got 24-30 hrs. Once I see clear goes pump, heat plate, and upstairs I go. At this point extraction can determine whether you get shatter, crumble,or, what I use...."Honey-Ball"!!! I do not care for the shatter because...just shatters. No heat during extraction from the dish can produce the crumble, I like to slowly warm dish over burner on oven quickly, and in small increments......heat and scrape, heat n scrape with a razor blade. Product builds up on blade#1 as you scrape since you've warmed it. Scrape off buildup of product on #1blade with your #2blade straight onto a PARCHMENT. Repeat the "heat and scrape" across the surface of pie dish until all oil has been collected and put in a pile on PARCHMENT paper. Fold around carefully warm from bottom just a it all together, roll it into a ball, then I stuff it in a concentrate jar I saved from dispensary.

Alchimia Staff

Tim Alchimia 2021-09-13
Some good advice here, thanks for the tips!


William 2019-11-22
When running the vac pump do you leave it run or shut it off during the whole process . I've heard that people leave the pump running for 24 to 38 hours. And then I've heard shut it off when you have pressurized the canister and release pressure in about a hour and repeat

Alchimia Staff

Tim Alchimia 2019-11-25
Hi William, thanks for your question. It's a matter of personal preference really, some extractors do as you suggest, getting up to vacuum and switching the pump off, while other will prefer to run the pump constantly for the entire purging process. From what I understand, the purge will be quicker if the pump is activated the whole time, but either method will do the trick. I hope that clears things up for you, all the best and happy extracting!


Mike A 2019-03-30
This guide shows some HORRIBLE practices, like blasting directly into a silicone dish, or letting the majority of the butane evaporate when its still in a pyrex, and then scraping it up. Jesus, you BHOtards give everyone a bad name. Ever wonder why there are GIGANTIC CHUNKS OF SHIT floating in the butane mixture in that green dish? It's because butane can leech into and dissolve silicone, so you're literally smoking your green dish every time you dab. Instead, ONLY blast into pyrex or stainless steel, and have parchment paper nearby that you can dump the butane/oil mixture into once it gets around the viscosity of warm honey. That way you have no nasty shit in it, and you can just put the parchment directly in the vacuum chamber. Once you let it firm up and then scrape it (or agitate it much at all, for that matter) it will create a nucleation point that lets moisture and air into the matrix, causing it to turn into butter. That's why your stuff looks like a sponge - because you scrape it. If you just poured it while it was still liquid and then let the last bit of butane evaporate off without messing with it, then you'd get nice, glassy shatter.


A dab maker 2018-12-19
Most of the advice here is unsafe. The pictures all have unsafe materials for purging, (silicone, parchment paper, etc..) And I can guarantee that the "finished" product that was in the picture, still had way too much butane in it.


A guy 2017-11-04
Mine always come out flat and same color .. looks like bottom pic of final product i n your blog...i was wonder how to get it more clear in color not purity or is that using co2 and will always come out more on the amberish color...ive always used butane and seems to have the same taste as well... whats the recommended temp using "skillet" while in first few steps mayb i have it to warm? Any tips on getting better taste im using good product not clipping....

Alchimia Staff

Dani Alchimia 2017-11-06
Hi A guy, Harvest time has some relationship with the colour of any extract, as well as processing, drying/purging and storing conditions (temperature, light, etc). Also, if you want to get clearer extracts I'd recommend to use fresh plant material (after 3-4 days od drying at most). I used to dab with a skillet some years ago, I simply heated it red-hot and then waited until it cooled down and looked grey again. That was the perfect moment to dab, at least for me. Hope it helped!


Mel 2016-08-28
What is the best way to seal a rip in the silicone gasket on the vacuum chamber?

Alchimia Staff

Dani Alchimia 2016-08-30
Hi Mel, The best thing you can do is purchasing another silicone gasket (you'll easily find it at any DIY store). Some people put vaseline or silicone vacuum grease between the gasket and the chamber to facilitate the process. Best of luck!


Michael 2016-06-14
Is it posiable that you Can combine a great komplet set with pump, chamber...... Actuely everything i need for the process. Thank you.

Alchimia Staff

Dani Alchimia 2016-06-15
Hi Michael, This BHO purging kit includes everything you need. All the best!

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