Supercritical fluid extraction (SFE) is the process of separating components from each other by use of a particular type of solvent. These types of solvents are labelled “supercritical” by virtue of the fact that when they are exposed to extreme temperatures and pressures, they display structures that fluctuate between intermediate states of solid, liquid, and gaseousness. When in this state, supercritical fluids are capable of breaking down structures where they can then be separated, or fractioned. Among the variety of supercritical solvents used for this process, the most common by far is CO2.
There are several reasons why CO2 is particularly useful within botanical extractions, namely with cannabis: CO2 is a naturally occurring compound. It exists all around us and our bodies produce it. As far as non-polar solvents are concerned, CO2 is among the safest. In fact, the FDA has labelled CO2 safe for industrial extractions, making it a much less controversial solvent than petroleum based hydrocarbons such as butane or propane. The conditions that allow CO2 to change from a fluid state to a supercritical state can occur without having to exceed temperatures above 90°F, meaning there is less risk of compromising the natural volatile compounds found in cannabis. CO2 is also unique in that its solubility will change with pressure, allowing for fractioning of the many different types of biomolecules available in cannabis strains. CO2 extraction can be used to pull various cannabinoids from the plant such as THCA, CBD, CBG, THCV as well as terpenes and other compounds.