co2 extraction

Effective CO2 Extraction: Supercritical vs. Subcritical

by | Jun 4, 2019

co2 extraction

Written by Keilah Keiser

Not long ago cannabis extraction conducted via highly flammable hydrocarbons used to be a risky, small-scale affair—the kind of thing amateur chemists performed in their garages and backyards, with notoriously explosive consequences. And while people still do dangerous extractions, legalization has spawned safer production methods, including CO2 extraction.

In the modern era of cannabis consumption, extracts have become more popular than ever. However, it’s not just popularity that’s changing the game for cannabis. Patients and recreational users are increasingly concerned with purchasing reliable, consistent, and safe methods of cannabis extracts.

Whether vaporizer pens, salves, edibles, or elixirs, chances are if it’s a quality cannabis product, it’s been produced using some form of carbon dioxide (CO2) extraction technology—a non-toxic, environmentally-friendly way to create potent concentrates saturated with cannabinoids and terpenes geared towards the modern consumer. Yet, CO2 extraction is a broad term that houses a couple of different methods under its umbrella. Below, we look at two different CO2 extraction processes, supercritical and subcritical extraction, and how they are changing the game for cannabis extracts.

LIQUID CO2 extraction

How Does CO2 Extraction Work?

CO2 extraction uses pressurized carbon dioxide to pull specific compounds from a plant. It’s the most expensive, effective, and safest extraction method because it removes the many dangers that come with solvents.

Although relatively new in cannabis concentrate processing, this technology is anything but green to the botanical extraction and food industries. In fact, carbon dioxide has been used as a standard extraction method for years from producing carbonated soft drinks and removing caffeine from coffee beans to crafting essential oils.

Today the use of CO2 for cannabis extraction is quickly positioning itself to be one of the leading technologies in the industry. Retailers (more now than ever) are labeling their concentrates by extraction method, detailing whether solvents were used and to what extent— igniting an effort to eliminate the use of petroleum-based solvents such as butane or propane and moving towards more modern supercritical and subcritical CO2 processes.

But what exactly is the difference between subcritical and supercritical extraction?

Supercritical CO2 Extraction

At standard temperatures and pressure, CO2 is a gas. However, when heated above 31.10C (critical temperature) and 1,071 psi (critical pressure), it exudes both the properties of a gas and a liquid, becoming what is called a supercritical fluid, and the start of the supercritical CO2 extraction process.

This supercritical liquid acts as a solvent and can slide into porous materials in addition to dissolving them. So, in the application of cannabis, the supercritical fluid passes through a chamber containing raw cannabis material, gently dissolving the membrane of the trichomes to capture their active compounds. Next, the compound-enriched solvent passes into another pressurized separation vessel. As pressures and temperatures fluctuate, compounds such as cannabinoids and terpenes are fractionated away. Finally, the remaining CO2 is transferred to a condenser vessel where the temperature and pressure allow the fluid to stabilize back into a gas.

While supercritical extractions produce a greater yield and take less time than subcritical extractions, they are too harsh for some terpenes—resulting in a loss or a transformation of these compounds.

co2 extraction

Subcritical CO2 Extraction

Subcritical CO2 extraction is the same kind of process; only it requires less pressure and lower temperature (non-supercritical liquid) than supercritical CO2 extraction. This process is longer, less efficient and produces smaller yields, but it retains and protects fragile constituents like essential oils, terpenes and other sensitive chemicals within the plant, which is highly desirable when producing full-spectrum cannabis products.

These temperature and pressure differences result in very different cannabis products. Supercritical systems produce a substance with the consistency of peanut butter. Higher temperatures and pressures used in supercritical systems can extract much larger molecules such as omega 3 and 6 lipids, chlorophyll and waxes which can then be removed through a process called winterization—leaving behind just cannabinoid oil. Subcritical CO2 extraction produces a substance with a consistency closer to molasses, which, as mentioned above, preserves additional cannabinoids besides CBD.

Which is Best: Supercritical or Subcritical?

Up until recently, supercritical CO2 extraction was the most commonly acknowledged method of CO2 extraction, but as more emphasis is placed on full-spectrum plant products and the role of terpenes in cannabis products, subcritical CO2 extractions have challenged common thought and practice. 

The argument being that the medicinal impact of the whole plant is greater than the sum of its parts—or what scientists refer to as the “entourage effect,” a hotly debated topic of the cannabis industry.