AUTHORED BY: GENESTER WILSON-KING, MD FACOG & SARAH RUSSO
Terpene Extraction: A General Overview
Terpenes are extracted from cannabis in two main ways. They can be carbon dioxide (CO2) extracted or steam distilled (hydrosols). Both methods capture volatile oils (i.e. essential oils) which are a complicated mixture of compounds with a low boiling point and primarily composed of low molecular weight terpenes. Here’s a breakdown of the different methods.
This process has a wide range of parameters to extract material. There are two phases of extraction using the CO2 method. Phase one extracts the terpenes and essential oils. Phase two draws out the rest of the plant constituents including cannabinoids, lipids, and other components. [1,2,3]
It is typical for most CO2 operators to begin processing (phase one) cannabis material via subcritical measures. The subcritical state consists of lower temperatures and pressures. This is to separate the essential oils (low molecular weight molecules) from the rest of the plant. 
The next phase of extraction consists of increasing the temperature and pressure, forcing the solvent into a supercritical state. This will extract the remaining cannabinoids and other compounds of interest.
The diagrams below illustrate the process. Temperature is on the X-axis and pressure is on the Y-axis.
Graphs courtesy of Travis Simpson
Figure 1 shows the different phases of the plant as it goes through CO2 extraction. Solid materials are seen at lower temperatures. As the temperature and pressure increase, it changes to the supercritical phase. Figure 2 shows that during the subcritical state, the temperature decreases but pressure remains the same. Also, the subcritical phase can occur if the pressure decreases but temperature remains the same.
The following flowchart illustrates the phases:
Flow chart courtesy of Travis Simpson
To give an analogy, subcritical is like making tea with cold water. Additionally, cold brew coffee pulls different compounds than hot water. Hot water extracts more tannins into the brew. So the benefit of using various extraction phases will give the ability to extract a wider variety of compounds from botanicals. 
According to Travis Simpson, a Phytochemist and Herbalist, in the subcritical phase, CO2 is more selective toward low molecular weight constituents similar to steam distillation. Carbon dioxide extraction can also be operated in a supercritical phase (higher energetic state, higher temperature and pressure) to extract larger molecular weight constituents such as cannabinoids, lipids, and potentially flavonoids. As CO2 goes into its supercritical phase, it is able to capture a larger constituent spectrum. CO2 captures a greater diversity of oxygenated terpenes such as nerolidol and eucalyptol. [1,4]
The most common plant essential oils on the market are generally created by distillation. Steam distillation is exclusive for the capturing of essential oils. The process utilizes boiling water to generate steam. The steam is passed through the plant material and carries the essential oils in the vapor stream to a condenser where it is liquified. The essential oil separates and floats on top of the water. Some of the oxygenated terpenes remain in the water and produce a mixture known as a hydrosol. 
There is a difference in the composition of essentials oils depending on the method of extraction. Well researched literature states steam distillation produces a higher concentration of hydrocarbon terpenes such as myrcene and beta caryophyllene.  In addition, steam distillation can be done with fresh plants as opposed to dried. The extraction can be performed in the field which avoids having to transport the plant material for processing. [2,3,5]
No matter the extraction technique, it is important to ask about the conservation of terpenes of any cannabis product you buy. Ask the producer what method they use and how they ensure that the source terpenes from the cannabis plant are being preserved in the final product.
- Simpson, Travis. (2020, August 1) Personal interview.
- Morrow, Kenneth. (2020). Terpenes, Hydrosols and Essential Oils: A Primer. Cannabis Business Times. Accessed on 7/1/2020
- Ziegler, H. (Ed.). (2007). Flavourings: production, composition, applications, regulations. John Wiley & Sons.
- Medicinal Plants.US. (2011) LOW-MOLECULAR-WEIGHT TERPENOIDS, PHENYLPROPANOIDS, AND VOLATILE OILS. Accessed on 07/28/2020
- Dhifi, W., Bellili, S., Jazi, S., Bahloul, N., & Mnif, W. (2016). Essential oils’ chemical characterization and investigation of some biological activities: A critical review. Medicines, 3(4), 25.
Genester Wilson-King, MD FACOG is a Board-Certified Obstetrician and gynecologist with over 25 years of clinical experience providing compassionate and research-driven care to patients. After years of working as a full-service OB/GYN, she founded Victory Rejuvenation Center (VRC), a private holistic and preventive medicine practice that provides life-transforming management modalities and customized medicines to patients. She is the Medical Advisor to Treadwell Farms.
As the Medical Director of VRC, Dr. Wilson-King provides services that help her patients age gracefully and achieve holistic well-being. She focuses on plant-based medicine, integrated health, nutrition, supplements, cannabis education, and hormone balance.
Dr. Wilson-King is Co-Vice President of the Society of Cannabis Clinicians (SCC). The SCC is an educational and scientific society of physicians and other professionals dedicated to the promotion, protection and support of cannabis for medical use. Dr. Wilson-King co-authored the Best Practices Guidelines for Cannabis Use in Pregnancy and Breastfeeding, and Cannabis Use in Women – Special Considerations (in progress). She is also on the Board of the Doctors For Cannabis Regulation (DFCR), the first and only national physicians’ association dedicated to the legalization and regulation of cannabis for adults. Advancing the DFCR’s commitment to addressing the disproportionate criminalization of cannabis use among communities of color and the nation’s poor, she regularly provides expert opinions for legal cases involving cannabis.
Dr. Wilson-King is a nationally recognized advocate, clinician, and educator for cannabis and hormone and wellness therapies. She presents on cannabis use in obstetrics and gynecology, hormone therapy for PMS, various stages of menopause, and for applications in nutrition.
Sarah Russo is a longtime plant enthusiast and globetrotter. She got her degree in environmental studies and social justice, with a focus on plant medicine from the Evergreen State College. She is a freelance writer, consultant, and project manager with over 13 years of experience in the cannabis and herbal medicine space. Her main objectives are fighting for the right to use plants, implementing social justice approaches in the cannabis industry, as well as encouraging sustainable agricultural practices. She is currently based on an island in the Mediterranean. Sarah is a content creator for Treadwell Farms.