Extraction of cannabidiol, or CBD, from hemp is the first step in producing concentrated medicines.
Cannabinoids like CBD are produced and stored by the cannabis plant in the tiny, frosty-looking trichomes that dust the flowers and sugar leaves of the plant. Typically these cannabinoids are extracted by immersing the plant material in a solvent which liquifies the trichomes. The solvent is then filtered of plant material* and then distilled to remove the solvent leaving behind the cannabinoids, terpenes (important, odor-causing components) and some plant fats and waxes.
This initial concentrate has different names depending upon the process. By far the most common is BHO - butane hash oil - named such because butane is the solvent used. BHO is common because it is cheap and pretty simple to do, but it’s also quite dangerous (many household explosions/fires owing to people not understanding how to handle these materials), and the product produced requires further processing to remove unwanted plant materials.
Probably a more accurate name for this class of concentrate would be AHO - alcane hash oil - because any number of the alcane hydrocarbons (butanes, hexane are most popular) can be used as the solvent.
At Boltz to Nutz Farm we do not use any alcanes hydrocarbons for extraction, though we do use ethanol extraction for those phenotypes that cannot be effectively pressed.
After BHO, the next most common solvent used for extraction is carbon dioxide. Not in the gaseous form however. In order for CO2 to act as a solvent to those trichomes, it must be in its supercritical, liquified state. This means keeping it under significant pressure to prevent it from changing to its gas phase.
CO2 extraction is much slower than hydrocarbon extraction, but it’s considerably safer for the operator and free of any concerns of trace solvent in the end product.
Like BHO, however, CO2 extracts require further processing to remove unwanted plant materials.
That “further processing” I’ve mentioned for both BHO and CO2 is a process called “winterizing.”
Winterizing is a process where the extract is diluted with another solvent, typically ethanol, to form a tincture and then chilled to and held at a very low temperature for period of time so that plant fats and waxes “crash” out of solution. It’s a bit like the fat on gravy turning solid in the fridge, except these solids are still mixed in the tincture instead of floating on top.
With the fats and waxes solidified, the tincture is then filtered (while cold) of these unwanted plant materials.
Ethanol can also be used as the primary extraction solvent, provided it's kept cold (below -40 F) if kept in prolonged contact with the biomass. Unlike BHO or CO2, ethanol will also extract water-soluable components of the plant, including chlorophyl which is undesirable, if allowed to warm.
It’s important to note that unwanted/undesirable plant materials are not always unwanted. Both RSO and FECO are full spectrum medicines that intentionally keep the plant fats and waxes and even chlorophyll for their medicinal properties.
For our primary lines at Boltz to Nutz, we use "solventless" rosin pressing to extract the plant oils. In this extraction technique the biomass placed inside a nylon mesh bag with a specific mesh size determined by the final use of the extraction. Finer mesh means less plant material will be extracted along with the target resins, however overall yield will be lower.
These filled mesh bags are then pressed between hot metal plates. The heat and pressure force the plant resins to liquify and then flow through the mesh for collection. The product of this type of extraction is called rosin and it does not, in general, required winterization, except when the end product is meant to be vaporized and inhaled. In that case, removal of plant waxes is useful.