If the recent outbreak of vape-related illnesses has taught the cannabis industry anything, it’s that we’re just scratching the surface of what we know about this plant and its compounds.
There is no main suspect in this rash of illnesses which has claimed 34 lives and made 1,604 people sick (as of press time, Oct. 28), according to the Centers for Disease Control and Prevention (CDC). Early reports pointed toward vitamin E acetate, a cutting agent used safely in nutraceutical and topical formulations but that has not been studied or approved for use in vape concentrates. But CDC investigations have not identified a single product linking all cases, except that most (not all) patients report a history of using THC products.
These recent reports have highlighted the need to take a closer look at how concentrated cannabis compounds, even in their purest form, respond to 21st-century methods of extraction and high-heat consumption. Terpenes, the natural aromatic compounds that drive both scent and effect characteristics in cannabis, are some of the volatile variables that should be considered as the industry seeks a better understanding of extraction and its impact on consumption.
A Closer Look at Terpenes
Terpenes are natural compounds found in many animals and plants. They comprise the largest class of natural products, with 75,000 known, structurally diversified compounds. Multiple studies have attributed a large range of pharmacological properties, such as anti-cancer, anti-microbial, anti-fungal, anti-viral, anti-hyperglycemic, analgesic, anti-inflammatory and anti-parasitic to this big family of compounds. Terpenes have been an important source of medicinal products for millennia and continue to have employment in the fields of medicine, pharmacy and general biology.
As of 2017, more than 560 unique chemical constituents have been identified in cannabis, with more than 100 unique cannabinoids and more than 150 individual terpenes reported. Data presented in a 1996 paper titled “The Volatile Oil Composition of Fresh and Air-Dried Buds of Cannabis Sativa,” by Simit A. Ross and Mahmoud A. Elsohly, “show that fresh bud oil is mainly composed of monoterpenes (92%), with 7% sesquiterpenes and approximately 1% made up of other chemical classes such as simple ketones and esters.”The authors also found, “not unexpectedly, drying the plant material resulted in overall reduction in the percentage of the oil recovered. Most of the loss appears to take place during the first week of drying. … [Drying] the plant material results in a significantly greater loss of monoterpenes than sesquiterpenes. However, qualitatively speaking, none of the major components of the oil (>0.1% of the total) completely disappeared in the drying process.”
Regarding most of the terpenes available in the market today, multiple sources are available:
- Organic food-grade terpenes (derived from plants and fruits)
- CO2-extracted, fractionalized terpenes (derived from cannabis)
- Steam distillation, hydrodistillation and steam/hydrodistillation (utilizing cannabis)
- Thin-film distilled (utilizing cannabis)
Each of these terpene-extraction and isolation methods carries its own potential problems.
The Science of Distillation and Extraction
The cannabis-derived terpenes sold to extractors are not what consumers—and sometimes manufacturers—think they are. Hydrosols are not pure cannabis terpenes in composition, but rather a byproduct derived from distillation. Most true essential oils are produced by distillation.
The term distillation is derived from the Latin word distillare, which means “trickling down.” In its simplest form, distillation is the evaporation and subsequent condensation of a liquid and typically produces artifacts of the original composition caused by oxidation, thermal degradation (i.e., heat), chemical degradation and chemical conversion.
The term essential oil is a contraction of the original quintessential oil. This definition stems from the Aristotelian idea that matter is composed of four elements, namely fire, air, earth and water. The fifth element, or quintessence, was then considered to be the spirit or life force. Distillation and evaporation were thought to be processes of removing the spirit or life force from the plant. This is also reflected in our language since the term “spirits” is used to describe distilled alcoholic beverages such as brandy, whiskey and eau de vie. The last of these (from French: “water of life”) again makes reference to the concept of removing the life force from the plant.
There are multiple distillation processes used, but in all of them, water is heated to produce steam, which carries the most volatile chemicals (terpenes are classified as volatile organic compounds) and essential oils of the plant material with it. Then, the steam is cooled in a condenser, with the resulting distillate collected in a separate container. Whether using steam distillation or hydrodistillation or a combination of the two, the resulting hydrosols are basically the same and are equally problematic.
Steam vs. Hydro Distillation
Steam distillation is the most efficient form of distillation and the most versatile. (For an in-depth explanation, I suggest reading “Hydrosols or Distillation Waters: Their Production, Safety, Efficiency, and the Sales Hype” by Martin Watt.) Although many oils are produced by steam distillation, they all lack the vibrancy of the oils collected without being exposed to heat, as sensitive compounds could be thermally degraded and/or hydrolyzed.
One of the many disadvantages of water or steam distillation is oxygenated compounds such as phenols. Phenols have a tendency to dissolve in distilled water, so their complete removal by distillation is not possible. Essential oils with high solubility in water and those susceptible to damage by heat cannot be separated through steam distillation. The compounds also must be steam-volatile for steam or water distillation to be feasible. Therefore, essential oil obtained by distillation does not represent the natural oil as it originally occurs in plant material.
Another disadvantage of steam or water distillation is that complete extraction is not possible, and that certain esters are only partly hydrolyzed, and sensitive substances like aldehydes, which are highly reactive, tend to polymerize or form undesirable byproducts. Proper extraction of essential oils occurs only by the process of expression or solvent extraction.
Before discussing the basic principles of essential oil production, it is important to understand that the essential oils people have in bottles or drums are not necessarily identical to what is present in the plant. With a few rare exceptions, it is wishful thinking to consider an essential oil to be “the soul” of the plant, and thus an exact replica of what is present in the plant. Only expressed oils that have not come in contact with heat or aerial oxidation may meet the conditions of a true plant essential oil. The chemical composition of distilled essential oils is not the same as that of the contents of the oil cells present in the plant or with the odor of plants growing in their natural environment.
A great example is rose oil. A nonprofessional individual examining pure natural rose oil, even in distillation, will not recognize the plant from which it was sourced. The alterations caused by hydrodistillation are remarkable: As the plant material comes into contact with steam, it undergoes many chemical changes. Hot steam will decompose terpenes, and aldehydes and esters may be formed from acids generated during the vaporization of certain essential oil components. Some water-soluble molecules may be lost by solution in distillation water, thus altering the oil’s fragrance profile.
Distillation produces essential oils and a byproduct called floral water, or hydrosol, hydrolate, herbal water and essential water, which are aqueous byproducts of distillation. They are colloidal suspensions (hydrosols) of essential oils as well as water-soluble components obtained by steam or hydrodistillation from plants and herbs. Distillates are used for flavorings, pharmaceuticals and cosmetics. Herbal distillates are produced in the same or similar methods as essential oils, but the appropriate term for the resulting product, essential water, is more descriptive and appropriate.
In the past, these essential waters were considered a byproduct of distillation. Today, they are considered co-products. The science of distillation is based on how different compounds vaporize at different temperatures. Unlike other extraction techniques based on the solubility of a compound in either oil or water, distillation will separate a multitude of compounds from the plant matter (although some will be lost in the water). The distillate will contain compounds that vaporize at or below the temperature of distillation. The actual chemical components of any distillate have not yet been fully identified, but distillates will contain some essential oil compounds as well as organic acids and other water-soluble plant compounds.
Compounds with a higher boiling point will remain behind and will include many of the water-soluble plant pigments and flavonoids. Herbal waters contain diluted essential oils. In addition to aromatic chemicals, these distillates also contain many more plant acids than pure essential oils, making them skin-friendly.
Cosmetics and toiletries manufacturers have found many uses for herbal distillates, but floral water (hydrosols) are unfit for human consumption via inhalation. (Do not vaporize, smoke or “dab” hydrosols.)
Challenges with Food-Grade Terpenes
As of yet, it is impossible to re-create the odor and flavor of the 150+ terpenes that exist in various cannabis cultivars or cultigens using food sources such as fruits and plants. It’s also unclear how many of these food-grade terpenes are safe to inhale—the data does not exist regarding vaping or dabbing.
The CO2 extraction process typically utilizes dried plant material, where a percentage of terpenes are lost to evaporation. Then, processors extract the dry material using pressurized CO2 gas. Any remaining moisture in the plant material contributes to the formation of carbolic acid and a phenol, an aromatic organic compound that tends to homogenize the odor and flavor of whatever terpenes remain. Some extractors super-dry their material, destroying and evaporating even more terpenes.
Steam and/or hydrodistillates are not whole terpene compositions. Some are simply hydrosols being sold for $10 per drop. These hydrosols contain minimal percentages of terpenes and only a small percentage of the available 150+ terpenes available in cannabis. Steam and/or hydrodistillates produce destroyed, converted artifacts of the original terpene composition from the original plant material, which includes any true distilled terpenes, as well.
Thin-film distillation units can process and distill many forms of extract ranging from cold-fluid extraction to CO2 extraction to ethanol extracts and so on. But terpenes are lost and converted by heat in this distillation process, creating artifacts and fractions. Therefore, it is impossible to produce a distillate that has the odor and flavor of the original plant material.
The Advantages of Heat-Free Extraction
Headspace technology is a unique method allowing for the capture of the volatile constituents of oil cells, providing additional information about the plants. Clive Christian, a British perfume company, describes headspace technology as “a process used to capture the odor compounds present in the air surrounding an object. This provides perfumers with the data needed to re-create a synthetic scent from something in nature that isn’t extractable via traditional methods.” In other words, this method has made it possible to detect the volatile components of the plant’s “aura.”
I suspect the phytochemical percentages cited in Ross and Elsohly’s 1996 paper would be very different if researchers looked at modern-day cultivars using a heat-free extraction and analytical method, such as cold headspace trapping. Existing data comes from U.S. cannabis labs that often lack more effective terpene testing capabilities, such as cold headspace trapping. (Cold headspace trapping is almost exclusively used in the fragrance industry.)
The chief benefit of hydrocarbon, ethanol and CO2 extraction is that a consistent temperature can be maintained during the process. This allows extracted oils to have a more complete odor profile. For example, very delicate aromatics like jasmine and linden blossom cannot survive the process of distillation. To capture their magical aromas, processors use a solvent extraction process.
The most aromatic extractions occur at or below ambient temperatures, which prevents thermal degradation of the compounds. The solvent extraction process uses the selectivity of the solvent with no heat application, oxidation, degradation conversion or destruction of the original composition.
Terpenes and the Future of Pharmaceuticals
Effective drug development depends on multidisciplinary collaborations, such as those among botanical, phytochemical and biological disciplines. Worldwide sales of terpene patent-based pharmaceuticals in 2002 were approximately US$12 billion (“Terpenes and Derivatives as a New Perspective for Pain Relief: A Patent Review Expert Opinion”). With the real medicinal value of cannabis compounds, such as cannabinoids and terpenoids, just beginning to be explored, expect a multibillion-dollar cannabis pharmaceutical industry to emerge someday.
So, are terpenes safe?
The extracts of cannabis, both cannabinoids and terpenes, are very complex, and very little is known regarding consumption in concentrated form. I believe that cold-solvent extraction yields far superior products than steam or hydrodistillation with respect to terpene extraction, isolation and preservation. Also, I think terpenes derived from pure cannabis are higher in quality, and represent a fuller terpene profile and composition than simple hydrosol or floral water. Hydrosols, again, are not fit for heated inhalation.
That being said, I have not yet found correlating data that unequivocally states that elevated or concentrated levels of terpenes are healthy to inhale, and too many questions remain to make safe assumptions about concentration levels and toxicity thresholds of each terpene. Again, these questions are in regard to pure terpenes, not hydrosols, which contain only small percentages of terpenes.
It should be possible to relate the intake of high doses of the substances to observed toxicity, yet efforts to evaluate the safety of a natural product based on its chemical composition and the variability of that composition’s phytochemistry for the intended use are in their infancy. The chemical constitution of a natural product is fundamental to understanding the product’s intended use and factors affecting its safety.
Recent advances in analytical methodology have made intensive investigation of the chemical composition of a natural product economically feasible and even routine. High-throughput instrumentation necessary to perform extensive qualitative and quantitative analysis of complex chemical mixtures and to evaluate the variation in the composition of the mixture is now a reality. In fact, analytical tools needed to chemically characterize these complex mixtures are becoming more cost effective, while the cost of traditional toxicology is becoming more cost intensive.
Based on the wealth of existing chemical and biological data on the constituents of essential oils and similar data on essential oils themselves, it is possible to validate the safety of a natural mixture based on its chemical composition. By looking at the interaction between one or more molecules in the natural product and macromolecules, such as proteins and enzymes, we can understand the biological response, regardless of whether it is a desired functional effect, such as a pleasing taste or a potential toxic effect, such as lung damage.
The most disturbing issue regarding the sale, formulation and heated inhalation of concentrated essential oils and hydrosols is that there is no correlating data supporting either a pro or con for use related to inhalation at elevated temperatures in part or as a whole composition of a matrix of terpenes. A healthy threshold must be established for the industry to confidently sell its products without worrying about getting patients and consumers sick. As it stands, people who are dabbing or inhaling hydrosols for which they pay $10 a drop are being used as test subjects.
From all substantiated data above, it’s clear that cold-solvent extraction—such as the cold expression of fresh, undried plant material—produces the highest-quality terpene extracts and that hydrosols and formulations of a few food-grade terpenes can’t completely recreate the flavor or odor of living plant characteristics. (A mixture of many cannabis terpenes also has an inevitable color tone. Purified compounds and mixtures of a few, such as hydrosols and floral waters, can be clear in color, but mixtures of many terpenes have color.)
Research and recent lessons learned are reminders that we as an industry should be mindful of how we present our products to ensure we’re not misrepresenting the contents or the safety of our patients’ and consumers’ favorite products.