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Cannabis extraction has grown to be a field of great importance within the modern cannabis industry. Extracts of cannabidiol (CBD) have become an enduring part of the medical cannabis space, and whole-plant cannabis extracts of tetrahydrocannabinol (THC) have led the recreational cannabis market to develop everything from vape oils to candy edibles.
The extraction stage can be key to the form and the application of the final product. For example, a CBD extract that’s meant for medicinal use will usually be made in such a way that naturally enriches the total CBD content and takes the form of an oil-based product, free from contaminants, that can be easily ingested. This is different to what you might desire when making vape oil for the recreational market, where the vaporization and inhalation requires increased purity and a complete absence of any trace residual solvents.
In the past, options for cannabis extraction were extremely limited. For thousands of years, hashish (a substance made from the sticky trichomes on the surface of the cannabis plant) was made by hand rubbing or sieve rubbing dried cannabis plants to form bars of the sticky cannabis resin; nowadays this process is often aided using high-pressure compression machinery.
The adoption of high-tech industrial machinery and chemical apparatus is allowing the cannabis industry to break free from the extraction methods of the past to experiment with new and exciting approaches. This has allowed new forms of cannabis extract, such as oral tinctures, vape oils, and wax concentrates to enter the market.
The three most popular extraction techniques to be adopted by the cannabis industry are alcohol extraction, hydrocarbon extraction, and supercritical CO2 extraction; but there are several niche alternatives that are beginning to gather attention from industry leaders.
The traditional ‘Big Three’
Alcohol extraction, also commonly referred to as ethanol extraction, is one of the most efficient extraction methods for processing large batches of cannabis flower, and can be done in hot, cold, or room temperature conditions.
Hot alcohol extraction is generally accomplished using the Soxhlet extraction technique. This method cycles hot alcohol solvent through the solid cannabis flower, stripping the cannabinoids and terpenes from the flower in the process. However, the method can be difficult to scale up to large batches, and often extracts unwanted chlorophyll and plant waxes from the cannabis flower due to the polarity of the alcohol solvent that requires several post-processing clarification steps to fix. Cold alcohol extraction helps to avoid this problem, as the cooler temperatures make it a little harder for the unwanted polar plant waxes and chlorophyll to dissolve in a polar ethanol solvent.
In terms of overall scalability, ease of post-processing, and energy efficiency, room temperature ethanol extraction appears to win out over its hot and cold counterparts. Likened to using a “giant tea bag and teacup,” the process involves submerging cannabis flower in a vat of room temperature ethanol solvent. Once the cannabis “teabag” is removed, the resulting ethanol/cannabis oil solution can be gradually heated to remove the solvent and leave behind a high-purity cannabis oil containing the most common cannabinoids.
Hydrocarbon extraction, normally achieved using butane or propane, is able to extract a greater variety of terpenes from the cannabis material than the alcohol extraction method. For products such as vape oils or oral tinctures, where the cannabis extract is unlikely to be masked by other flavors, preserving these terpenes helps to give the extract flavor and aroma.
This improved extraction comes as a result of the low boiling point of butane, which is around -0.5°C or 31°F at standard pressure. After cold butane solvent has washed over the cannabis plant material and extracted its oils, the butane solvent can be easily cold-boiled off to leave an oil with more of a “whole plant” character, as more of the temperature-sensitive terpenes will be retained.
However, like the alcohol method, hydrocarbon extraction cannot be so easily scaled up to deal with large single batches of cannabis material. While the low boiling point of butane, and the even lower boiling point of propane, is advantageous when you want to remove the solvent without removing any other organic compounds, these volatile and flammable solvents present a safety hazard to workers. Hydrocarbon extraction is a very hands-on process and is rarely automated, meaning that there is almost always a human worker in close proximity to the extraction vessel. In the interest of safety, hydrocarbon extraction is done on a much smaller scale, though the speed and efficiency of this extraction method means its overall output still makes it suitable for large-scale operations.
Supercritical CO2 extraction
Supercritical CO2 extraction is still considered by some to be somewhat of a newcomer to the cannabis industry, but it’s already a popular choice. The method itself has been around for decades, and is already commonly used in other industries for the processing of products such as coffee, tea, vanilla, and perfumes.
In brief, the method involves using specialist pressure and temperature control equipment to turn gaseous CO2 into a supercritical fluid. When passed over cannabis material, the fluid can easily extract plant waxes and oils from the cannabis.
“Every extraction method has unique advantages and drawbacks,” explains Lo Friesen, the founder and CEO of the Seattle-based cannabis company Heylo, which uses a tailored version of the CO2 extraction technique.
“Our proprietary method, which we call RawX, aims to retain as much of the plant’s original chemical profile as possible. This stems from a philosophy that the best cannabis extracts are the ones that are the ‘closest’ to the actual flower. The method has two fundamental steps: source high quality material, and respect it at every stage of extraction.”
“With CO2, that means for us processing under relatively low pressures and temperatures over a long period of time and minimizing the amount of post-processing that’s done after extraction. In some cases, we don’t require any post processing, so the oil that comes out of our CO2 system can go directly into vape cartridges.”
The most common criticism leveled at CO2 extraction is that the high upfront costs that come with the scientific equipment needed can be prohibitive for start-ups or small businesses. But at Heylo at least, Friesen and her team believe this investment was worth it to find a method that suits their philosophy.
“While CO2 requires a higher initial capital investment, the advantages this method offers made it the obvious choice for long-term viability.”
“Unlike alcohol or butane, CO2 is a highly tunable solvent, meaning you can pull unique compounds from botanicals at different pressures and temperatures. This opens the door for a ton of creativity in the extraction process, which was attractive to us. CO2 is also safer than many hydrocarbon techniques which use flammable and toxic solvents like butane.”
Novel methods and new advances
While the three methods listed above are the most commonly used cannabis extraction methods, there are several more novel processes that are nudging their way into the cannabis extraction space, either as improvements to existing technologies or as new extraction methods in their own right.
Movers and shakers: Ultrasound-assisted extraction
Ultrasound-assisted extraction is a relatively straightforward strategy that can be used to enhance the efficacy of alcohol extraction methods. The process harnesses sound energy, in a process known as ultrasonication, to form microbubbles in the solvent medium. These microbubbles will collapse violently within a few microseconds of their formation, creating tiny localized hotspots that can reach temperatures of around 5000 Kelvin and pressures above 500 bar. These extreme conditions produce powerful hydro-mechanical shear forces that can disrupt the cell walls of botanical materials, allowing the plant’s natural oils to dissolve into an alcohol solvent more readily.
This can help to combat the problems caused by the polarity of ethanol and other common alcohol extraction solvents in cannabis extraction. Naturally, because of its polar nature, ethanol more readily dissolves undesirable water-soluble molecules such as chlorophyll rather than the non-polar cannabinoids. By using ultrasound assistance, the non-polar cannabinoids from within the cannabis plant are more able to dissolve into the alcohol solvent; improving the extraction efficiency of the alcohol method and leaving behind a cannabis extract with enhanced levels of the main cannabinoids which is less likely to need extensive post-processing clarification.
Industrial-scale ultrasonication machines are already available commercially for the extraction of antioxidants and vitamins from herbs and plant matter, but as of yet the technology doesn’t appear to have been widely adapted for the cannabis industry. Perhaps as the CBD and the cannabis extract industries grow more producers will be looking to optimize their operations in this way.
Take it for a spin: Hydrodynamic extraction
Ultrasound assistance can be helpful outside of ethanol extraction. Hydrodynamic extraction technology has recently been introduced to the cannabis industry, which utilizes a combination of temperature, pressure, and ultrasonication to create full spectrum cannabis extracts from whole fresh cannabis flower.
In the hydrodynamic extraction process, fresh cannabis flower is frozen and then broken down directly using ultrasonication and hydro-dynamic forces. This produces a nanoemulsion that contains all the cannabinoids, terpenes, and other oils from the cannabis plant in an aqueous phase. Centrifugal separation, followed by low-temperature vacuum distillation and drying steps, turn the nanoemulsion into a potent and highly bioavailable cannabis extract.
Because the entire process can be conducted at low temperatures and doesn’t require the use of additional industrial solvents, the final extract preserves a great number of cannabis’ aromatic compounds. This gives the product a strong flavor and aroma that closely matches the original cannabis strain used in the extraction; which may be of particular interest to those involved in making vape cartridge oils who want to give their customers that “whole plant cannabis” experience.
A sweet idea: cannabis honey
In a far cry from the expensive equipment used in other extraction methodologies, a new (and somewhat avant-garde) extraction method is turning to mother nature for help with the extraction process.
The Israeli cannabis technology company PhytoPharma International made headlines late last year when it announced that it had successfully produced a cannabis-infused honey made solely by bees.
Bees are insects, and so do not have the same mammalian endocannabinoid system that humans and other mammals have. When fed on cannabinoids, the bees’ bodies naturally pass on the compounds to infuse them with the honey produced by the colony. In essence, the bees’ bodies become a cannabis extraction machine.
The end result is natural honey that’s infused with ultra-low concentrations of active cannabinoids. Despite the low cannabinoid levels, studies done by PhytoPharma on the efficacy of its honey showed it to be highly bioavailable. Additionally, PhytoPharma reported that the honey was able to produce a positive medical effect, curbing the effects of fibromyalgia pain and PTSD-induced insomnia. While this method is not a typical large-scale industrial extraction method like the others listed above, it certainly appears to be a viable commercial cannabis extraction venture.
What is next for the industry?
Historically, improving extraction efficiencies has been a large driver behind the development and implementation of new extraction techniques. Now it seems that more bespoke extraction solutions that emphasize the protection of aromatic compounds or promote bioavailability are also starting to appeal to segments of the cannabis extraction market.
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