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 percent 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.
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.
Written By: Skunk Pharm Research,LLC.