Butane Honey Oil, or BHO, is the essential oil from the cannabis plant, extracted using Butane as a solvent. It can be extracted from fresh material or from cured material as a Concrete or a Oleoresin. A concrete or an oleoresin that has been winterized to remove the waxes, lipids, and fats, is known as an Absolute.
Butane Honey Oil extraction refers to the method used to extract the essential oils from cannabis, and there are multiple theories on the best way to accomplish this, as well as what material is best to use.
Perhaps the first question is why use a BHO technique to extract the resins, instead of just boiling the material in alcohol to get the greatest amount of extracted material?
The answer to that is that because butane is relatively non polar, it doesn’t extract the water solubles like chlorophyll and plant alkaloids. Butane produces one of the cleanest extractions, albeit typically at a lower yield than polar alcohol.
Using closed loop extractors, we average slightly more than 20% oil by weight from bud, but as low as 5.7% absolute and as high as 28.1% absolute.
The first wash will usually extract 75 to 80%, leaving the balance for the second after repacking the column. The second extraction will be more sedative and less heady. If you use a hand microscope, you can easily see when the trichome heads are gone and the stalks look like wet fur.
We’ve only tried a few processes here at the pharm, and used to cover simple flow through columns, and using a thermos bottle, but now cover only closed loop systems, because of the number of brothers and sisters ignoring my caveats to not extract indoors.
We currently use a closed loop system for BHO, and I cover that process on separate threads named The Terpenators, where I will detail building our Mk I through second generation automated systems.
Before we discuss how to extract the essential oils from cannabis, let us talk about the plant material to be used. That immediately brings to mind the qualifying question, “What do you want to use it for?”
Oil that is to be vaporized, is normally treated differently than oil that is used orally or topically, because it doesn’t need to be decarboxylated. For cannabis concentrates to be orally and topically active, it does require that the THCA and CBDA be converted to THC and CBD, by a heating or drying process. I will cover that issue under a separate thread on Decarboxylation, so as to not clutter this post.
Besides the cannabinoids, which are Di-Terpene alcohols and di-alcohols (diol), there are also other terpenes in cannabis essential oils, which add to its smell, flavor, and medicinal entourage effect. Some of these terpenes are highly aromatic alcohols, phenols, ketones, aldehydes, ethers, and esters, which are aromatic because they freely give off molecules at even ambient temperatures.
Heating the plant material or the oil to decarboxylation temperatures will evaporate off most of these smaller aromatic Mono-Terpene and Sesqui-Terpene molecules, before the larger and heavier cannabis Di-Terpenes are affected. Decarboxylated oil is smoother to the taste, but basically tastes like hash, with the floral undertones gone.
Gone also are the medicinal and entourage effects from those terpenes. The price we pay for decarboxylation, so we shouldn’t decarboxylate casually, and should first consider the end use before picking the process.
One of our process limitations, is that though non polar, n-butane has slight water solubility. At 20C/68F, it is only 0.0325 by vol/vol, but not zero and is still enough to pickup undesirable water solubles. 1 liter, or 1000 ml X 0.0325 = 32.5 ml of water.
With water, comes water solubles, which includes chlorophyll and plant alkaloids, that detract from the taste, so the dance is to maintain the volatile terpenes, while studiously avoiding the water solubles.
Freezing the water is one method that works well, but it is important that the material be dry when it was frozen and that it is not exposed to high humidity while frozen, or ice will form over the trichomes, preventing their extraction.
Another method is to simply remove most of the water. This will produce pristine extractions, but doesn’t preserve the terpenes. If the material is to be decarboxylated anyway, that is of little concern, because we will lose them anyway.
We also have the issue of purging out the remaining butane, while preserving the terpenes. Again, there are a number of ways to do that, but I will address only a few of the ways that have worked for us here. Those are light heat, high heat, and thin film vacuum.
So, besides decarboxylation, what are some of the things to consider selecting a process and how should the plant material be prepared?
In our experience, for best flavor and taste, freshest material works best (less than 3 weeks old), whether it is fresh frozen material or dried. Older cured material loses the nuances of the floral undertones and just tastes like hash. That means that the degree of drying and curing is also critical, if your goal is to maintain maximum terpene content.
Oil from buds is tastier than oil from even sugar trim, because most of the terpenes are produced by the buds, and that is where they are the most plentiful. Tasty is usually not a word used to describe oil from fan leaves or stems, though effective may be.
The absolutely most flavorful BHO extract to me personally and to the test panels thus far, is fresh picked buds, that are immediately frozen to tie up the water, and extracted while still frozen. It produces an oil that abounds in whimsical flavors darting about and the word most often used to describe it by panel members, was the word “fresh.”
Next most flavorful, from a BHO standpoint, is material that has only been cured 5 to 7 days, and is at the small stem snap stage, where you might jar it if you were curing it to smoke.
Part of the formula is of course the degree and methods used to purge out the remaining butane. While there are a number of ways to do that as well, I will address only a few of the ways that have worked for us here. Those methods are low heat, high heat, and thin film vacuum.
Lastly, selecting a suitable butane source is a key step, in that all butane sources aren’t created equal. n-Butane boiling point (30.2°F -1°C) is a simple alkane, with four carbon atoms linked together in a row, with the remaining possible carbon bonding sites taken up by hydrogen atoms. Iso-Butane is three carbons in a row with the forth carbon attached to the middle carbon in a “T” like conformation. This conformation change also alters the boiling point (10.94°F/ -11.7°C) and also the specificity.
The simple alkanes all are gaseous at room temperature and atmospheric pressure. They are removed from crude oil before it is further processed, by simple heating. The simplest is Methane, which is only on carbon and four hydrogen atoms, followed by Ethane with two carbons, Propane with three, and Butane with the four.
Pentane is the next simple alkane, the first to be liquid at room temperature and the first to have zero water solubility. From Pentane on, the simple alkanes are named from the Greek alphabet, and are Hexane, Heptane, Octane, etc, on through the light naphthas, oils, waxes, and asphalts.
The formula for all simple alkanes, is the number of carbon atoms times two, plus two, because each carbon atom has four possible bonding sites. A mnemonic device for remembering the first four alkanes, which were named before the Greek system was applied, is Mary Eats Peanut Butter.
After removal from the crude oil, the gases are typically de-sulfurized using steam and a catalytic reactive bed, and fractionally distilled into the four basic gases. As fractional distilling separates the gasses by specific gravity, the principal contaminants in n-Butane at that point, will be Iso-Butane, a branched molecule isomer of n-Butane, as well as n-Propane, and Cyclo-Propane, plus low levels of heavier, longer chain molecules than C-4, and which are often referred to as Mystery Oil.
Neither of the butanes or propanes are particularly toxic at any sort of reasonable levels, nor is C-5 Pentane, but C-6 Hexane is and a third party forensic lab analysis of canned butane reveals the presence of molecules as long as c-18 as contaminates at the parts per billionth level.
We advise pre-distilling your butane to remove any mystery oil, prior to extraction. It is easy to remove from the butane, but hard to remove from the concentrates afterwards. See https://skunkpharmresearch.com/vacuum-distilling-butane/
The following for instance is taken from a typical MSDS sheet for n-Butane. The Rat LD-50 (50% dead) is 658000 mg/m3 4 hours. That is breathing a 65.8% pure butane atmosphere and asphixiating.
Section 11. Toxicological information for n-Butane; Diethyl; Freon 600; Liquefied petroleum gas; LPG; n-C4H10; Butanen; Butani; Methylethylmethane; UN 1011; UN 1075; A-17; Bu-Gas.
Carcinogenic effects No known significant effects or critical hazards.
Mutagenic effects No known significant effects or critical hazards.
Reproduction toxicity No known significant effects or critical hazards.
No specific information is available in our database regarding the other toxic effects of this material to humans.
Chronic effects on humans May cause damage to the following organs: central nervous system (CNS).
Other toxic effects onhumans
Butane LC50 Inhalation Vapor
Rat 658000 mg/m3 4 hours
Product/ingredient name Result Species Dose Exposure
Products of degradation: carbon oxides (CO, CO2) and water.
Section 12. Ecological information
Products of degradation :
Environmental fate : Not available.
Environmental hazards : No known significant effects or critical hazards.
Toxicity to the environment : Not available.
The MSDS LD-50s on Iso-Butane, Propane, Cyclo-Propane, and oleaginous waxes are as follows:
n-Propane; Dimethylmethane; Freon 290; Liquefied petroleum gas; Lpg; Propylhydride; R 290; C3H8; UN 1075; UN 1978; A-108; Hydrocarbon propellant. LC50 Inhalation Gas: Rat >800000 ppm 15 minutes
Cyclopropnane; Trimethylene; Trimethylene (cyclic); UN 1027; No LD-50 established;
Iso-Butane; 2-methyl-; Trimethylmethane; 1,1-Dimethylethane; 2-Methylpropane; isoC4H10; i-Butane; Isobutane mixtures; UN 1075; UN 1969; R 600a; tert-Butane; A 31;Methylpropane; Propane, 2-methyl-isobutane LC50 Inhalation Vapor Rat 658000 mg/m3 4 hours
Oleaginous Waxes– Paraffin, no notable toxicity or LD-50 available
n-Butane is used for any number of things, so it is processing beyond this point, or sharing storage tanks with other contaminated sources that may create health concerns. While n-Butane is non-toxic enough used as a food propellant, if it is to be used as a stove fuel, it will in most cases have an odorant added for leak detection, as n-Butane has only a very light sweet petroleum odor.
Ethyl Mercap is most often added for that purpose, and is the familiar rotten egg smell is detectable at the astonishing low concentration of under 3 parts per Billionth! Hexane (Gasoline) by comparison, has an odor threshold of around 30 parts per millionth, or about 10,000 times more is required for us to smell mercaptoethanol.
The MSDS for Ethyl Mercaptan shows 4420 ppm/4 hour(s) inhalation-rat LC50; 682 mg/kg oral-rat LD50, with the target organs being the central nervous system. Not super toxic, but tastes and smells of rotten eggs, so that point may be mute.
Butadiene may be added to stove fuel as well, and is of serious concern. While the following typical MSDS example shows relative low toxicity, take a look at the carcinogenic effects.
LD50 Oral Rat 5480 mg/kg -LC50 Inhalation Vapor Rat 285 g/m3 4 hours
LC50 Inhalation Vapor Rat 285000 mg/m3 4 hours
LC50 Inhalation Gas. Rat 128000 ppm 4 hours
Mutagenic effects No known significant effects or critical hazards.
Reproduction toxicity No known significant effects or critical hazards.
No specific information is available in our database regarding the other toxic effects of
this material to humans.
CARCINOGENIC EFFECTS: Classified 1 (Proven for humans.) by IARC, 1 (Known to
be human carcinogens.) by NTP, + (Proven.) by NIOSH, 1 (Proven for humans.) by
European Union. Classified A2 (Suspected for humans.) by ACGIH.
MUTAGENIC EFFECTS: Classified 2 by European Union.
May cause damage to the following organs: the reproductive system, mucous membranes, upper respiratory tract, skin, eyes, central nervous system (CNS).
Here is another n and Isobutane toxicology division of the Texas Commission on Environmental Quality.
Of note, is that the FDA has rated n and Isobutane as GRAS, or Generally Recognized As Safe.
Food and Drug Administration, HHS
§ 184.1165 n-Butane and iso-butane.
(a) n-Butane and iso-butane (empirical formula C4H10, CAS Reg. Nos. 106– 97–8 and 75–28–5, respectively) are colorless, flammable gases at normal temperatures and pressures. They are easily liquefied under pressure at room temperature and are stored and shipped in the liquid state.
The butanes are obtained from natural gas by fractionation following absorption in oil, adsorption to surface-active agents, or refrigeration.
(b) The ingredients must be of a purity suitable for their intended use.
(c) In accordance with §184.1(b)(1), these ingredients are used in food with no limitations other than current good manufacturing practice. The affirmation of these ingredients as generally recognized as safe (GRAS) as direct human food ingredients is based upon the following current good manufacturing practice conditions of use:
(1) The ingredients are used as propellants, aerating agents, and gases as defined in § 170.3(o)(25) of this chapter.
(2) The ingredients are used in food at levels not to exceed current good manufacturing practice.
(d) Prior sanctions for these ingredients different from the uses established in this section do not exist or have been waived.
[48 FR 57270, Dec. 29, 1983, as amended at 73 FR 8607, Feb. 14, 2008; 76 FR 59249, Sept. 26, 2011]”
n-Butane may also be further refined to increase its purity, or to make it suitable for use in butane lighters. R-600 Refrigerant and Instrument grade n-Butane are examples of higher purity n-Butane suitable for extractions, and are distributed by suppliers like Praxair and Airgas. As those sources are expensive and not usually available to non commercial customers, in support of federal guidelines listing it as a controlled substance used in the manufacture of illegal drugs, some folks use butane made for butane lighters.
Each manufacturers blend is slightly different, with n-Propane usually added as a propellant, because below the freezing temperature of water, butane is a liquid instead of a gas.
They also further refine the n-Butane to remove more of the low level “oleaginous waxes” aka Mystery Oil, which clog the small orifices in expensive butane lighters. This is often shown on lighter butane cans as a number followed by an X. IE: 5X.
Here Madison Avenue has gotten a foot hold, and even 7X butane is available for even more money, though there is no advantage over a good 4X for the purpose of extraction.
One refiner has started labeling the brand names that they produce, Near Zero Impurities, guaranteeing under 50ppm impurities. An independent test showed that they in fact are under 50 ppm, and even under the 15ppm testing cutoff, as were competitors brands not touting near zero impurities.
If using lighter butane, the safest course is to use tried and proven brands, but if forced to improvise, first obtain a MSDS sheet from that specific manufacturer, showing the contents. Reject any containing mercaps or Butadiene.
Ingredients less than 1% need not be shown on the MSDS sheet, unless they present a health risk at the levels present, so they are not all inclusive, but a good place to start.
Here is a link to a study by Skyhighler ranking the different lighter butane brands by residual MO content:
Butane is highly flammable, so let us next talk about safety. First and foremost, always perform the extraction outside in a well ventilated area. Have a fire extinguisher handy, as well as a blanket to roll up in, should the unthinkable happen.
It goes without saying that smoking around a butane extraction is asking for a disaster, but I have literally grabbed the hand of folks starting to light up because they “forgot” where they were at and what they were doing. May I suggest that you leave your lighter and smokes somewhere else when you are doing extractions.
Same with your cell phone!
Wear no synthetic fabrics, including your socks, because static electricity sparks probably ignite more butane unintentionally than bone headed smokers.
We use a fan to disperse the butane rapidly so as to keep it from pooling. Butane is heavier than air and will collect in low spots given its own devices. We use a plastic fan so that no sparks are created by a piece of gravel or other hard material passing through the fan blades.
In dry cold conditions, we add a grounding strap to our cans, so as to not draw static electricity sparks between the can and the column.
See https://skunkpharmresearch.com/butane-safety/ for more butane safety detail.
Material prep will of course depend on the application, so lets cover that subject generally.
Fresh buds should be dry of standing water and cut into small pieces, before being stuffed into a column and placed in a -32C/0F freezer for 48 hours to solidify. Fresh frozen buds produce the most aromatic extraction.
Second best for for maximum terpene retention are buds broken up after 5 to 7 days hanging, or as soon as the small stems break freely. They should be jarred immediately to retain freshness and run as soon as possible to prevent molding.
When extracting dried buds for vaporization, or bragging rights, the material is broken up just loosely enough to extract, but not enough to expose excessive broken cell boundaries. That can be done by hand, or with a nugget buster. Here is an example of a nug buster design that I scored off Roll It Up forum, but alas I can’t remember the author: The wire cloth can be obtained from Howard Wire at http://howardwire.com/square_mesh.html
Buds for decarboxylation and most pristine appearance, should be placed on a cookie sheet and baked in a 94C/200F oven until just frangible, when rolled between the finger and thumb. They can then be ground or scrubbed through a pasta strainer to remove the sticks and stems. Or ground up and should be jarred after grinding, to keep moisture pickup low.
The material shouldn’t be bone dry as it will become too frangible, nor should a coffee grinder be used, because of the fines that it produces, that have to be subsequently removed.
We also dry our trim and leaves until frangible as above and scrub ti through a pasta strainer, using a leather gloved hand and firm pressure, so as to minimize the amount of fine particles generated.
Another more commercial version is a cement mixer and dry ice chunks to break up the material for extraction.
So now that we have covered some of the basics, lets move on to the different processes:
Simple Flow Through Column:
Simple flow thorough columns are sometimes used in a technique called open blasting, and we once had a section covering that technique, we have elected to remove it because of the number of brothers and sisters blowing themselves and others up blasting indoors, despite our dire warnings and instructions to the contrary.
It is always the few, that ruin things for the us’n masses, but their actions paint us all with the same brush in the public eye. If you have no alternative to open blasting, you can find ample instructions elsewhere on how to do so.
Butane is relatively easy to purge from cannabis oleoresins or concretes, as it has a boiling point of around -.5C/31.5F, or right about the freezing point of water. Given enough time just sitting around, it will purge below our 5000 ppm smell sensory threshold, and even our far more acute sense of taste, either of which is a small percentage of the 658, 000 ppm, that the MSDS LD-50 tells us it took to asphyxiate 50% of the test rats in 4 hours.
We can speed up that purge, by using a dish with a large surface area, relative to the depth of the pool of oil. Usually small extractions, so as to keep the depth thin, are the easiest to purge.
Air movement over the surface speeds up evaporation, by whisking away the saturated boundary layer and providing the extra energy for the molecules of butane to escape the surface of the oil. Care must be exercised here, as any dust or lint in the air will end up in the oil, so usually a cheese cloth or similar porous cover is placed over it, before blowing over the top with a fan.
We can also speed it up with the application of heat. Any heat will speed up the evaporation, and one line of thought is to keep the heat low and around 60C/140F, using a hot pad after the hot water bath. A typical purge might take an hour and provides maximum terpene retention.
When adding bottom heat, you can also add a loose fitting lid, which will speed up the purging and keep out lint and dust.
For a faster purge, the temperature can be raised to above the melting point of the cannabis essential oils, or around 82C/180F, to give the butane molecules maximum mobility.
Instead of heat, vacuum may be applied to speed up the purge process. That is the process that we use when we wish to maintain the cannabinoids in their carboxcylic acid forms.
In thin film vacuum purging, we place about an 3/16″ of the oil in a 6″ Pyrex Petri dish, and place that in a vacuum chamber, which also contains a hot plate. That allows us to manipulate both the temperature and atmospheric pressure, so that we can achieve boiling at very low, or even ambient temperatures.
While we use 180F to vacuum purge a raw oleoresin, adding heat isn’t necessary when thin film vacuum purging raw oleoresins redissolved in ethanol. The alcohol will boil away under 28.5″Hg at ambient temperatures, as will the water that is left behind, even without adding any heat.
Vacuum ovens are the most popular way to purge anything more than a few grams of personal stash. This is a subject in and of itself and is covered in depth on our Purging in a Vacuum Oven page.
For our oral and topical meds, we exclusively used the bain marie collection vessel, and simply wiped the water off the outside, following the hot water purge, and set it in an electric fondue pot full of hot 121C/250F Canola oil.
The residual butane will boil off first, exiting in larger, multi sized bubbles, followed by the smaller equally sized CO2 bubbles from decarboxylation.
Depending on the use, we remove it from the hot oil when the bubble activity suddenly slacks dramatically off, indicating the 70% peak of the decarboxylation curve, or when it becomes quiescent, if we are looking for maximum sedative effect.
Click the link below for typical residual solvent and mystery oil scan:
Hot oil Pots:
We use electric fondue pots for decarboxylation and I prefer the Quisinart, for their sensitive controls and narrow dead band. We also have a couple of Rivals, which work well too, but whose controls aren’t as sensitive.
Some fry cookers may have sensitive enough controls, but most are designed to primarily run at 375F, and lack control sensitivity, as well as have a large dead band at 250F.
It is important to make sure that the container is sitting on something that suspends it up off the bottom of the oil pot, to eliminate direct transfer hotspots. We keep several jar lid rings in the bottom of our electric fondue pots for that purpose.
We never trust any controls however, and use a good mercury lab thermometer, a digital, or an infra red optical pyrometer to establish and control temperatures.
Air stills such as the MegaHome essential oil or water distiller work great for purging or decarbing without the mess of a fondue pot. They also allow you to recapture the alcohol from a winterization step as well.
Thermos extraction is an open extraction technique allowing an extended soak period at atmospheric pressure.
Because it is an open extraction process, and because of how many brothers and sisters are blowing themselves and other up ignoring the warnings and open blasting indoors, we have removed instructions from this site.