Cannabis Extraction Processes
Traditional botanical extractions aim to provide the extracts in a readily usable form. Various methods have been used to create cannabis concentrates. It is important to understand the desired results and the reasons for using the extracts (e.g. medical, therapeutic or recreational). Within a cannabis processing plant, the extraction process (e.g. light hydrocarbon, ethanol, supercritical fluid or solvent-less) needs to be chosen. Regardless of whether the end product is a crude extract, a high-end consumable, or a pharmaceutical-grade formulation, an understanding of the physicochemical attributes (e.g. cannabinoid potency, viscosity, color, clarity or aroma) that drive that product quality will assist in making decisions about how to design a cannabis extraction process. When designing a cannabis extraction process, there are three key stages (preprocessing, extraction and purification) that will affect the properties of the resulting cannabis extract. Making decisions about those stages becomes much more straightforward when you understand the requirements of the end product.
The Basics of Cannabis Concentrates/Extracts
The main goal of cannabis extraction is to separate and collect desirable plant compounds (like cannabinoids and terpenes) from the plant matrix. Different extraction methods can be utilized to divide plant material into extracts (e.g. terpenes and cannabinoids) that deliver appealing flavors, scents and effects. The drying and storage of cannabis raw material can have an impact on the quality of the finished extract. If the goal is to deliver the traditional cured flavour of cannabis, then identifying the optimal temperature, humidity and moisture content will drive the development of that process step. The key is identifying how to undertake and measure the process step (e.g. moisture and terpene content). Another important preprocessing step is raw material size reduction. This step can improve the efficiency and quality of a cannabis extraction process. The goal of this process step is to decrease the particle size of the material to be extracted, resulting in an increased surface area available for solvent extraction. The goal of extraction processes is to deliver the bioactive components of the cannabis raw material as close to their natural state as possible in the finished extract while optimizing the efficiency of the extraction process. Several size-reduction variables (e.g. milling versus grinding, room temperature versus chilled, low-speed grinding versus high-speed grinding) may need to be compared. Understanding the extraction of target compounds (e.g. cannabinoids and terpenes) before and after the size reduction process will help to minimize degradation resulting from thermal or oxidative damage.
Solvent-based extractions (e.g. hydrocarbon, CO2 and ethanol) normally create concentrates referred to as “oils”. Some of these extraction methods are quite risky, expensive and difficult. Personnel should have the analytical skills and equipment to perform the extraction processes safely and effectively. Extractions need to be analysed with a professional testing laboratory to ensure the final product is safe for human to consumption.
Cannabis Extraction Methods
The heart of any cannabis processing plant is the extraction process which will impact on every physicochemical attribute of the cannabis extract being processed and will represent a significant portion of the capital outlay associated with the processing plant. Extraction methods include light hydrocarbon extraction, ethanol extraction and supercritical CO2 extraction.
Light hydrocarbon (e.g. butane and propane) extraction has commonly been used because of its low running cost and minimal equipment needed. This solvent system provides fast extractions and can be selective for cannabinoids and terpenes with limited co-extraction of other potentially unwanted compounds (e.g. chlorophyll and plant waxes) from the cannabis raw material. Light hydrocarbon extraction systems tend to be middle of the road in terms of capital cost but may demand a serious infrastructure investment (depending on local safety requirements) to create a safe working space. These extractions can be a risky because hydrocarbons burn very easily in the gas phase. A limited number of variables can be adjusted when producing a light hydrocarbon extract. The easy operation of hydrocarbon extraction systems means that the learning curve for operators is relatively simple. Because butane and propane are highly volatile compounds, post-processing steps (usually referred to as purging) may be required to remove the solvent from the extract. This purge step often involves heating the extract under deep vacuum conditions.
Ethanol extraction has become increasingly popular because of its speed of extraction, low capital cost and clear designation as a food-grade solvent. While ethanol is a less selective solvent than butane and propane, it will strip a wide range of compounds from the cannabis raw material. Ethanol extraction often needs to be coupled with post-extraction purification processes to remove unwanted co-extractives. As with light hydrocarbon extraction, solvent removal represents a significant time-consuming step. Ethanol evaporation requires more energy (compared to hydrocarbons), and the vast majority of volatile aroma compounds will be lost from the extract during solvent removal. If those compounds are not important to the end product, then this potential problem is a non-issue, but if your formulation is meant to leverage the entourage effect of cannabinoids and terpenes acting synergistically, then this may not be the ideal process. Ethanol extraction is time-consuming and risky because ethanol is highly flammable. This method may also present the challenge of co-extracting chlorophyll, which has a bitter taste. After the ethanol is evaporated, the concentrates are relatively safe to make and consume.
Supercritical carbon dioxide (CO2) extraction has risen to a place of prominence in the cannabis industry. Supercritical CO2 extraction relies on turning gaseous carbon dioxide into a supercritical liquid by applying temperature and pressure until a supercritical liquid form is attained. Its steep learning curve and high capital spend mean it is not the ideal choice for some, but the depth of tunability afforded by its solvent system gives the processor a level of control on the extract produced that no other process can provide. This tunability is due to a unique property of CO2 in the supercritical phase. By controlling the pressure and temperature of the extraction, the operator can alter the solvent characteristics of the CO2 and design a process to extract only the compounds that meet the goals of their end product. CO2 extracts do not require further solvent removal because it simply evaporates from the extract as it is collected from the extractor. This means that the operator can capture nature identical aroma profiles from their raw material. Cannabis extraction with CO2 can remove flavoursome cannabis compounds from the plant matrix with a clearer cannabinoid extract and higher yields. CO2 extracts are safer to consume even though the process of making them can be costly.
Analysis is important in the development of an optimized hydrocarbon extraction process. If simple efficiency and throughput is the aim of process optimization, it is critical to determine which vacuum pressure and temperature combination results in the fastest removal of the solvent from the extract to achieve a product that meets the regulatory specifications. To determine this, a residual solvent analysis must be performed on finished samples to determine how much solvent remains. If the result on a sample comes back above the regulatory specification, the process developer will need to increase the purge time, increase the temperature of the purge, or pull a deeper vacuum. Delivering a high level of terpenes may be critical both to the bioactive and organoleptic properties of the extract. This challenge adds complexity because the methods for improving purge efficiency (increased time and temperature) will also result in greater loss of terpenes. The residual solvent content and the terpene content should be analyzed at different temperatures and pressures throughout the purge process to understand how long it will take to produce material within specification.
Post-extraction purification can range from simple filtration (often referred to as winterization) to more complex processes (e.g. distillation or chromatography). Again, end product requirements will drive these decisions. Winterization leverages melting point differences between the various components in an extract to precipitate unwanted waxes at a reduced temperature. Distillation can purify extracts by selective evaporation and collection of fractions with high cannabinoid potency (and desirable color and low levels of undesirable components). Preparative-scale chromatography can purify the compounds in an extract based on their affinity to the stationary phase within a chromatography column. This process will provide high levels of cannabinoid purity (upwards of 95% pure). Crystallisation is a further process step which is used to prepare homogeneous preparations of cannabinoids In crystal form and purity.
The task of process development in the cannabis industry can be complex. The key to effective process development is having a complete understanding of the physicochemical attributes and the end product, and relying on analysis to provide feedback
Author Dr Craig Davis