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Cannabis terpenes have been a hot topic in the industry for the last several years. Gone are the days of flavorless distillates causing sub-standard user experiences. Today’s more seasoned and educated extract consumer demands the effects, flavors, and aromas indicative of the original plant material—that means capturing the terpenes native to the source. As the head of research efforts at Green Mill Supercritical, the extraction of terpenes is one of the most exciting and promising areas of the cannabis industry.
There are hundreds if not thousands of terpenoid compounds that have been identified in cannabis, spanning different classes such as monoterpenes, sesquiterpenes, di-terpenes, and more. Due to their impact on flavor, effect, and efficacy, terpenes are increasingly sought by cannabis connoisseurs. Thoughtful consumers who care about the tastes and smells of the product they inhale — students of terpene science whether they think of it that way or not — are noticing the results of some extraction process or another. Shatter, Wax, Budder, Rosins, Resins, Diamonds, and vape products of all types, are extracted. The range and concentration of terpenes and cannabinoids within — the “profile” of the product — are determined to a large degree by what extraction process is used.
Terpene extractions are not novel, but new technology is enabling the production of a full spectrum terpene profile with none of the downsides typically found in most common extraction methods. Based on recent validation of this technology, it seems apparent that supercritical CO₂ is the superior solvent and method for the extraction and isolation of light volatile compounds from any botanical biomass. To help you make wise decisions as you try to find the products that match your discriminating tastes, here are the most commonly used extraction methods.
The centuries-old process of steam distillation is conducted by adding heat to a reservoir of water in a still. The heated water will then generate steam, which in turn is diffused through a matrix of botanical material to volatilize the light volatile compounds. These compounds are then carried through the still to a condenser where the water, water solubles, and terpenes can be collected and separated.
The major problem with steam-distilled terpenes is that you are adding a lot of thermal stress (temps as high as 100°C) to the thermally-labile compounds, potentially causing degradation. Although steam distillation has been the go-to method for terpene extraction for ages, it has some clear disadvantages in the pursuit of obtaining terpene isolation true to the source material.
Vacuum distillation is a process in which the boiling point of all compounds is lowered when a vacuum is introduced into the reaction vessel of the distillation system. A lowered boiling point should mean being able to run at a lower temperature to get the same results. But this turns out to be true only if you are targeting the lower boiling point monoterpenes. To target a full profile of both mono and sesquiterpenes, the heat again needs to be raised under vacuum.
As a marker, let us consider the sesquiterpene α-humulene, a C15 (atomic weight) terpene found in both hops and cannabis. The compound’s boiling point under normal atmospheric conditions is around 260°C. Even under vacuum conditions as low as 5mmHg, the compound still requires a temperature of around ~105°C to reach its boiling point. Concerns over the thermal degradation of lower molecular weight, thermally-labile monoterpenes still apply here.
Organic solvents (ethanol, propane and butane)
Ethyl alcohol is a poor solvent for terpene extractions because you cannot selectively extract and isolate the terpene compounds. An ethanol extraction pulls out both the terpenes and cannabinoids, requiring the solvent to be purged, which can cause a loss or degradation of the light monoterpenes from the overall profile.
The situation with the hydrocarbon gases, propane, and butane, is much better compared to ethyl alcohol as they are easy to purge post-extraction. This is why there is a prevalence of high-terpene hydrocarbon-extracted products in the cannabis market. Unfortunately, the hydrocarbon solvents are not able to isolate the terpene compounds alone, making it extremely inefficient (one reason consumer products are so expensive). The technology also uses a highly flammable solvent derived from fossil fuels.
Subcritical carbon dioxide
In recent years, liquid carbon dioxide, also known as subcritical CO₂, has been a popular solvent for terpene extractions in the cannabis space. Liquid CO₂ requires temperatures below 31°C. However, when conducting a liquid CO₂ extraction the solvent density will always be above 0.800 g/mL. The higher density means a liquid CO₂ extraction for light volatiles will always co-extract other compounds such as cannabinoids and waxes which will dilute the terpene fraction and affect the terpene extract quality, increasing viscosity and darkening the color of the extract significantly.