Story by Mat Lee
With all the talk of closed loops, BHO, RSO, supercritical CO2, ZHO, PHO, EHO and the other fun acronyms people give to the kind of oil they are extracting, I thought it would be a good time for an extraction primer.
I will start this off by saying that I don’t recommend anyone open blast or closed loop extract unless they know what they are doing and have the proper safety measures in place. They alsoshould make sure they are abiding by state law regarding extractions. This stuff can be very dangerous if not fully respected. It can also be safer than your drive to work when done properly and with the right equipment. This article is for informational purposes only.
Now that that’s out of the way, let’s define some terms and concepts. This will provide a better understanding of what is actually going on inside of the extraction chamber.
We will start out with closed loop Butane Honey Oil (BHO) extractions and then talk about supercritical CO2 extractions.
So what is a hydrocarbon? It’s a compound made up of hydrogen and carbon. Hydrocarbons are the solvent of choice for the majority of extractors out there.
What is a solvent? Basically, a solvent is any substance used in an extraction to isolate a compound or group of compounds from a specific matrix. Water, butane, propane, hexane, ethanol, and CO2 are all considered solvents. The example I like is brewing coffee. Water is the solvent that extracts caffeine and other stuff from the coffee beans. The coffee beans are the matrix.
Many different solvents can be used to extract cannabis oil. The more popular ones are butane, CO2, propane, and ethanol. Water is also a solvent, but that’s more for making hash, which is a kind of concentrate, but not something I personally consider good for dabbing. (Although, of course, some forms are.)
BHO is obtained by packing a column full of fresh or dried plant material or kief, then introducing a hydrocarbon in liquid form, usually butane in one of its various different structures, such as N-butane and isobutane.
The main difference between isobutane and N-butane is the structure of the carbon chain. N-butane has a chain of four carbon atoms in a row, while isobutane has three carbon atoms in a row, with the fourth attached to the C-2. It’s confusing and doesn’t really matter to most people doing extractions, but I think it’s interesting. If you stand up and put your arms up and out like a Y, then invert that—that’s basically what isobutane looks like.
To extract in a closed loop, introduce the hydrocarbons into the chamber with the plant material, either by soaking it or just quickly rinsing it over the cannabis. Then, allow it to drain into a collection vessel. After that, start reclaiming the hydrocarbons and get them pumped back into your recovery tank. This completes the loop.
Open blasting is using glass tubes packed with plant material and then blasting butane froma can through the material. Of course all of the butane is just hanging out there, or getting blasted into the atmosphere, so you can see why it’s frowned upon. Open blasting is very unsafe not only for the people doing the blasting, but for anyone who happens to be around.
Moving hydrocarbons around is mainly a matter of temperature differentials. If you heat a tank of butane slightly and cool the chamber the plant material is in, the solvent will be inclined to move to the colder vessel. Heating it just speeds up the process. But remember, heating hydrocarbons will build up pressure, so know what you’re doing and have the right gear if you are going to attempt this. Which I should say again, I do not recommend.
Once the oil has been collected, it will need to be purged in a vacuum oven of some sort. This is where a lot of the magic happens, not to mention eliminating the solvents in the oil. Depending on the temperature, vacuum, and duration of the purge, you will end up with completely different materials. You’ve heard the terms “shatter,” “wax” or “butter” before? This stage determines the consistency of the material. The quality of solvent, flower, and purge time all figure into what the final material will look, smell and taste like.
Some people go with a long, slow purge under vacuum to try and keep as much of the natural terpene content in the material as they can. Remember, terpenes are quite volatile, so if you get your material too hot, you lose a lot of what gives oil its taste and smell.
Others prefer the hot and fast method, which not only purges out all of the solvent, but a lot of the more volatile terpenes, as well as decarboxylating the THCA by converting it to THC and releasing carbon dioxide in the process. Usually when this is done, other refinement steps are occurring, and terpenes are being reintroduced to give it some flavor. The method you use will depend on your goal for the final product.
You also can winterize the material, which basically uses ethanol to remove the lipids and waxes from the extract. Of course if you do this, you should have a good way of concentrating down your boozy material. Letting it sit out in a dish evaporating isn’t very efficient or time-friendly.
Now let’s review supercritical CO2 extraction. Basically CO2 can be heated or cooled to act as a solvent, using different pressures. When under high pressure the CO2 goes into a supercritical state. This means that it basically has the properties of a liquid while still technically being a gas. It will expand in the container and go through solids like a gas, but with the density and ability to dissolve compounds like a liquid. When low pressures are used, it is considered a subcritical CO2 extraction.
Subcritical tends to extract material that is lighter in color and with a higher terpene content than supercritical. When done right, these extractions produce a higher terpene content than normal BHO extractions, but the gear required to do them is much more expensive, with what seems like a slightly higher learning curve. If you see a vape pen cartridge with material in it that has a darker red tint, that is usually CO2 oil.
Another form of BHOis live resin. It can be a lot of things, but in my experience it’s called live because the plant material used in the extraction is as fresh as it can possibly be. If done right—keeping everything as cold as possible to preserve the natural terpene profile of the plant—you can produce something that, unless you’ve tried it, you wouldn’t believe.
Rosin, a solventless extraction method, is hotly debated in cannabis forums all over the internet. Some say it is, some say it is not an extraction. For the sake of this primer we’ll say it is. Rosin uses existing moisture in the plant material, heat, and pressure, in order to gush the oil right out of the bud. There are numerous methods for doing this using anything from a hair straightener and some parchment paper, to task-specific heated machine presses. It definitely produces some tasty stuff if you have the right bud and technique, and I recommend this method to anyone trying to make a little oil for themselves. Do this before you make the move to open blast. It’s much safer.
There’s definitely a garbage in, garbage out effect with extraction. The more garbage material going in, the more equipment and engineering education you’ll need to make a good product. When I say garbage, I mean trim, old moldy bud, or stuff with 10% or less THC content in it. You’ll get a nice extract if you put in the time to refine the oil, but it will take a lot more time refining than if you had started with better input material. Fresh buds in an ice cold chamber will always make better live resin or shatter than old crappy buds.
In the end, be safe and smart when working with flammable solvents. Be diligent and enjoy the fruits of your labor.