As the cannabis industry matures, terpene isolation from cannabis plant material has become a primary issue. So far, there have only been two practical applications: steam distillation, which is time consuming and smaller in scale, or CO2 extraction, which requires expensive equipment and an experienced operator. Solvent-free microwave-assisted extraction solves these problems with a cost-effective, efficient solution. The process requires nothing other than water, takes roughly 1 h per run, and yields tetrahydrocannabinol (THC) free, strain-specific terpenes from a variety of starting materials. Throughout this article, I discuss the capabilities of microwave-assisted extraction and how the cannabis industry can utilize it.
The terpene yield by weight seen on cured OGKB 2.0 plant material was 1.59%, again beating the tested analytical value of 1.46% seen on the cured flower. The isolated terpenes were then sent out to a third party analytical laboratory for terpene and potency profiling. The results were similar to the fresh frozen sample sent out, yielding nondetect on cannabinoid levels and a total terpene content of 68.35%. This material produced clear terpenes that can be seen in Figure 3, as most material does; however, varying shades of yellows and oranges have been seen in our laboratory throughout different varieties of cannabis. (See upper right for Figure 3, click to enlarge.)
What About the Cannabinoids?
While valuable, terpenes are only part of the equation in the economics of cannabis. The plant also has a value in the cannabinoids it produces. These molecules are still intact in the plant material after having the terpenes extracted. As seen in Table V, the total potential tetrahydrocannabinol (THC) in the post extraction fresh frozen plant material closely matches the values pre-extraction. (See upper right for Table V, click to enlarge.) Both of the samples tested were chosen at random. One considerable difference is that tetrahydrocannabinolic acid (THCA) is almost fully decarboxylated post-microwave assisted extraction. The plant material is varying shades of brown, a product of the Maillard reaction, and has an extremely high moisture content. We first attempted to simply freeze the material immediately after it was removed from the microwave then extract it using butane, similar to the production of live resin. However, the yields were found to be well below expected values. It was thought that the excess moisture in conjunction with freezing the material was a factor in the yield loss, so a forced air oven was then used to completely dry the microwaved material prior to solvent extraction. This change in process provided the mathematical yields expected after solvent extraction. A sample of the resulting crude oil was sent out for potency testing, further purified into THC distillate, and then sent out for potency testing again. The results can be seen in Table VI. (See upper right for Table VI, click to enlarge.) This process was done to ensure that there were no unexpected side effects in THC production on post-microwave assisted extraction, such as isomerization or potency degradation. No negative side effects were seen throughout processing.
We Have Terpenes, What Now?
The terpenes isolated can be used in numerous applications. They have a place in aromatherapy and topicals, but our facility uses them almost exclusively in the production of vape carts. We have found that by using cannabis-derived terpenes as the diluting agent for high potency distillate we have been able to produce a vape cartridge completely derived from cannabis that provides an unparalleled flavor profile, an example of which can be seen in Figure 4. (See upper right for Figure 4, click to enlarge.) These terpenes can also be added in higher amounts to other concentrate products (such as shatter or live resin) to produce what is known to the industry as a high terpene full spectrum extract (HTFSE, Figure 5). (See upper right for Figure 5, click to enlarge.) This type of extract sacrifices some cannabinoid potency to achieve an extremely high terpene profile, creating a unique effect and flavor.
Cannabis extraction methods are numerous and ever evolving, with innovations in equipment and technique almost daily. One of those innovations is microwave-assisted extraction. I hope that this article helped shed light on this technique and the possibilities it provides in terpene isolation within the cannabis industry. With new states coming online and opportunities to further research the properties and effects of the cannabis plant continue to open up, the need to efficiently isolate these compounds is only going to increase.
I would like to thank Chris Wren and the team at Medizin Las Vegas for cultivating some of the best cannabis in the world; Levon Shilling and Ryan Boyle from Milestone Srl for their continued support; and DB Labs for their thorough and accurate sample analysis.
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Stephen Markle is the Vice President of Production for Planet 13 in Las Vegas, Nevada, and is responsible for all concentrate and infused product manufacturing. Markle has over seven years of experience as an analytical chemist in the nutraceutical and cannabis industries. Direct correspondence to: [email protected]
How to Cite This Article
S. Markle, Cannabis Science and Technology 2(4), 50-57, 76 (2019).