Carbon dioxide (CO2) is an excellent choice of solvent for extraction of natural compounds. The technology has been used successfully in commercial applications for over 40 years, including hop extraction, herb and spice extraction, oilseed extraction, and coffee decaffeination. CO2 is non-flammable, non-toxic, cheap, and readily available in large quantities at high purity. The extraction process is carried out at near-ambient temperature preventing damage to heat-sensitive compounds, and small changes in process temperature and/or pressure can result in large changes to solubility.
For these reasons, the cannabis industry has adopted CO2 extraction as an ideal method for cannabis oil processing. Cannabis is an extremely complex plant containing over 550 unique chemicals identified to date, including cannabinoids, terpenes, phenols, flavonoids, fatty acids, pigments, and other miscellaneous compounds. Typically, the cannabinoid and terpene fractions collectively make up approximately 10-30% of the mass of buds. Though the larger residual fraction contains many beneficial compounds, it is the cannabinoid and terpene fraction that the industry is focused on for extraction and purification.
In a typical CO2 extraction, extraction parameters can be tuned to produce crude oil that contains 45-80% cannabinoids and terpenes. The remaining portion will consist of co-extracted components from the feedstock that are either highly soluble in CO2 at the given processing parameters; or, have low solubility but are easily accessible and co-extracted with limited mass transfer resistance. A process called winterization can be employed to remove the co-extracted fraction. In this process, the extracted crude oil is mixed with another solvent and exposed to cold temperature to precipitate some amount of the undesirable co-extracted solids. The solids are then separated from the liquid through a filtration process, yielding what is known in the industry as a “winterized oil.” Depending on the desired outcome of the process, the oil may be further processed or purified or formulated directly into retail products.
Winterization can be a time-consuming process and can be a rate-limiting step in some cannabis processing operations. Because of this, many manufacturers are touting equipment that can eliminate the need for this additional process. However, these claims generally cloud the truth by avoiding discussion of the pros and cons.
Can winterization be minimized or eliminated? The answer is yes, but a better question to ask is should it be? Read on for some tips on reducing winterization in CO2 extraction.
You get what you put in.
In general, extracting feedstock with a high content of desirable constituents will yield an extract with a high content of desirable constituents (provided these constituents are easily extractable). In other words, starting with high-potency, terpene-rich cannabis feedstock will yield a crude extract containing a high cannabinoid and terpene content. Conversely, starting with a low potency low terpene feedstock (i.e. trim or industrial hemp) will yield an extract with a higher content of non-cannabinoid, non-terpene material that will likely require winterization.
Reducing particle size will increase the mass of feedstock that can fit into a given volume (increase density) and increase the extraction efficiency by reducing the distance the solvent must travel to reach the center of a particle. However, reducing particle size ruptures plant cells and exposes their interior contents to the solvent. This increases the likelihood of coextraction of undesirables, which require removal using winterization.
One of the benefits of CO2 extraction is tuneability; solvent power is affected by changes in CO2 temperature and density. Thus, extraction parameters can be tuned to favor the extraction of a compound or groups of compounds with similar chemical properties. For example, Perrotin-Brunel et al (2010) examined the solubility of pure THC in CO2 and found that at extraction pressures lower than 2175 psi, THC solubility decreased with increasing temperature (density-dependent), and at pressures higher than 2175 psi, THC solubility increased with increasing temperature (temperature dependent).
Many cannabis processors choose to use cold (<60 F), low pressure (<1200 psi) liquid CO2, as terpenes are highly miscible under these conditions. Liquid CO2 is very dense, having low selectivity and high solvent power towards high molecular weight compounds. Further, the solubility of major cannabinoids in CO2 at these parameters is low, so more solvent contact is needed and thus, more time is required if cannabinoid extraction is the goal.
Alternative Separation Methods.
There are alternative methods of separation that do not involve traditional winterization techniques. As with many technologies used in the cannabis industry, many have been adopted from other industries. Decantation, for example, can be used to separate immiscible liquids with different densities. In the food industry, a centrifuge is used to separate cream from skimmed milk. Another example would include nanofiltration, which can filter fats from oil without the need to first freeze and precipitate the fats as solids.
Not all products require winterization.
Perhaps the goal of the manufacturer is to make a “broad-spectrum” oil that contains all the components, plant fats and waxes included, originally extracted from the plant material. Such an extract would most closely resemble the chemical makeup of the original plant material. Raw crude extract can either be packaged as-is or diluted with a carrier oil to achieve a desired cannabinoid concentration. Typical products would include capsules, tinctures, and syringes.
Extraction without winterization is possible, but its application to business processes is reliant on the feedstock, preparation, and parameters. Alternative extraction methods provide some options, while product options provide more. However, in the typical day-to-day world of CO2 extraction, companies need to be sure that their end goals are compatible with the requirements and outcomes of a winterization-free process. If somebody tells you that winterization isn’t required, be sure you are clear on the intended results.
If you need more information on extraction, with or without winterization, the Vitalis science team is able to help. Work with a team of experts that can back up their claims with science and data; a team that consistently assists customers in understanding the nuances of extraction and processing.
Perrotin-Brunel, H. et al. 2010. Solubility of Δ9-tetrahydrocannabinol in supercritical carbon dioxide. The Journal of Supercritical Fluids 52: 6-10.
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