Concentrated cannabis resin as well as isolated THC, CBD, terpene and other cannabinoid distillates function as a valuable tool in the medical world; allowing manufacturers to formulate products with precise dosages for patients in conveniently ingestible forms. As pharmaceutical cannabis gains acceptance for its efficacy, demand for extracts of many varieties will increase. But not all extraction processes are created equal. In this ongoing series, we will explore in depth the different types of extract, and the methodologies and science behind emerging and traditional technologies for extraction.
Full-Spectrum Extract vs. Distillate
In the world of medical cannabis, “full-spectrum extract”, or FSE, simply refers to concentrated cannabis resin. The extraction is done with the goal of keeping all of the cannabinoids and terpenes found in the original resin intact. FSE can be made using one strain of cannabis exclusively or a blend of cultivars, much like coffee or wine. Several studies have recently revealed that full-spectrum extracts are more effective in alleviating certain symptoms than treatments based on single compounds (either THC or CBD alone, for example) . Patient testimonial also supports this phenomenon, which scientists believe is due to both the presence of more medicinal chemicals, and the beneficial synergistic interaction of the chemicals, which is called the “entourage” effect.
Typically, cannabis resin contains around 113 different cannabinoids and hundreds of different terpenes. To produce an “isolate” or “distillate”, of a specific compound found in the resin, FSE is used as the starting material, and taken through a short path or wiped film distillation process. A technique called Partition Centrifugal Chromatography can also isolate some of the lesser known cannabinoids which are found in very low concentrations, for scientific research. This month we focus on methods of obtaining FSE using solvents. Any of the FSE extracts produced with these methods, as well as by Supercritical CO2 extraction, can be used as starting material for distillations of THC, CBD, CBG, d-limonene, α-pinene, etc. A future edition of “All About Extraction” will focus on making distillates from various “crude” extracts.
Solvent vs. Solventless
Many solvents can be used to extract the medicinal compounds from cannabis. Below, we will examine hydrocarbon and ethanol solvents, and reserve the rich topic of using Supercritical CO2 as a solvent for its own in-depth examination in a future article. The chemical properties of the substance determine how well it extracts the desired compounds as well as potentially undesirable ones. A solvent dissolves the plant resin, loosely binding to the cannabinoids and terpenes, and also to other compounds contained in the resin like waxes, lipids, and chlorophyll. A “polar” solvent, one which has an uneven distribution of electrons, attracts compounds which are also polar, and a “non-polar” solvent, with a more symmetric electron distribution, attaches more easily to molecules which are also non-polar. Cannabinoids and terpenes are large organic molecules, which have a few polar groups, but also contain lots of carbon-hydrogen symmetric bonds which are non-polar. The non-polar interactions tend to dominate based on the size of the molecules.
Extraction done without solvents can utilise either dry-sieve, press, or water-based techniques, including microwave agitation and sonication. None of the target compounds in the cannabis resin dissolve into water, so it is not considered a solvent. Water is extremely polar, and the medicinal compounds in cannabis are mostly non-polar, with only slight polarity. In next month’s issue, we will discuss solventless extraction techniques, from traditional artisanal methods to the latest technologies.
A popular method of extraction is to use a hydrocarbon solvent, such as propane, butane, or hexane, or a combination of these. Consisting entirely of symmetric carbon-hydrogen bonds, these compounds are extremely non-polar, binding easily to THC, CBD, terpenes and other cannabinoids. They also bind to the acid forms of cannabinoids such as THCA or CBDA, present in high concentration in freshly harvested material, although not as effectively as ethanol. Hydrocarbons have very low boiling points, and are usually in gaseous form at room temperature and atmospheric pressure, meaning they are extremely prone to combustion when exposed to heat. This is why one must always perform the extraction using a closed-loop system in a laboratory with an active exhaust hood, with no sources of heat or sparks.
Pressurised and chilled liquid hydrocarbon is injected through the plant material, dissolving the resin; the solution is then filtered through a small micron screen before going through vacuum vapour pump, which collects and condenses the hydrocarbon solvent for reuse. The resulting oil is placed in an evaporation device for further solvent purging: a vacuum chamber oven, or a Rotary or Falling Film Evaporator (FFE).
Because lipids and waxes are also non-polar, they too are extracted by hydrocarbons, along with the cannabinoids and terpenes, so the resulting concentrate is not a clear substance: it typically looks like and is referred to as “wax” or “budder”(like “butter”). Chlorophyll is also mildly extracted because it has a non-polar hydrocarbon tail, possibly contributing a slight green or dark colour to the extract. To achieve a clear, light coloured concentrate product, the extract is put through an additional process called “Winterization”. First, the wax or budder is placed into a food grade ethanol bath at room temperature. As the alcohol bath is cooled down to between -50 and-80°C, the waxes, lipids, and chlorophyll solidify in the cold ethanol while the THC, cannabinoids, and terpenes remain in aqueous form. This process usually takes 24-48 hours. The solution is then put through a micro-filter, allowing only the ethanol, THC, cannabinoids, and terpenes to pass through, filtering out the frozen solid compounds. The filtered solution is then put through a rotary evaporator or FFE to remove the remaining ethanol solvent.
Cryogenic Ethanol Extraction (CEE)
Ethyl Alcohol, or Ethanol, (C2O5OH) has been used historically as an effective solvent to produce cannabis tinctures and oils. Ethanol’s chemical structure makes it a unique solvent, capable of binding to both polar and non-polar compounds, because it contains both a polar hydroxyl group (OH) and also a non-polar ethyl hydrocarbon group. Because it is a small molecule, its polar and non-polar solvent capabilities have similar strengths. Scientific experimentation shows that ethanol and other alcohols extract THC, CBD, THCA, CBDA, terpenes and other cannabinoids and flavonoids more efficiently than hydrocarbon solvents .
With a boiling point much higher than most short chain hydrocarbons (78.37 C compared to Butane at -1 C), the risk of volatile explosions using ethanol is very low. However, at room temperatures, waxes, lipids and especially chlorophyll and other plant pigments dissolved much more readily into ethanol than into non-polar hydrocarbon solvents, yielding a dark, murky or green coloured concentrate.
Recently developed, Cryogenic Ethanol Extraction involves lowering the temperature of the ethanol to between -60 and -80 C, and then injecting the cold fluid over the plant material. The super cold ethanol still attracts cannabinoids, terpenes, and other medicinal compounds, however lipids, waxes, and pigments such as chlorophyll are solidified and much harder to extract. Thus, cryogenically processed ethanol extract does not require the second “winterization” stage to produce a clear, “shatter”- like extract.
The most efficient CEE technology is a closed loop system which utilises pressurised bursts of ethanol over the plant material in a vacuum chamber. The bursts are repeated several times over the same material, resulting in an extraction efficiency (EE) of 96-98% of the THC contained in the stock material with this method . Although this is the highest THC extraction efficiency of all known methods, the system behaves such that as extraction efficiency increases, the more chlorophyll is also present, and the medicinal purity of the product is lowered. Scientists continue to work on improving this crucial aspect of the process. Ethanol is recovered and purged from the concentrate using a Rotary or Falling Film Evaporator.
Both hydrocarbons and ethanol can produce high quality, full-spectrum extracts, maintaining the approximate composition of cannabinoids and terpenes found in the original flower material. Each solvent has its advantages and drawbacks, as discussed. Advances in technology and innovation in methodology continue to lead extraction scientists towards increasing the purity and and pharmaceutical precision of these valuable medicines.
By Sama’a Djomehri
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