What are cannabis concentrates?
Cannabis concentrates are the cannabinoids of the cannabis plant that have been extracted using one of the extraction methods described below. They are usually made by covering cannabis plant material with a solvent. After the solvent has extracted the cannabinoids from the plant material, the solvent is evaporated away leaving behind the extracted concentrated cannabinoid oil. They are significantly more potent than cannabis flowers and their applications as medicine have proven to be diverse and effective. The extraction of cannabis concentrates is a complex and potentially dangerous process. The methods required for proper extraction are so precise that individuals who produce cannabis extracts of especially high quality are considered extract artists. The science of cannabis concentrate extraction depends on the solubility of the cannabinoids and other active ingredients of the cannabis plant. A variety of suitable solvents is available for extracting the active ingredients from cannabis, but each of which has strengths, weaknesses, laboratory infrastructure requirements and production-scaling considerations. Because cannabinoids are not water-soluble, they must be dissolved in a solvent if they are to be extracted properly. Solvents are the chemicals used to remove the cannabinoids from the cannabis plant. When cannabis flowers are submerged in these solvents, the cannabinoids, terpenes and other active ingredients are dissolved into the solvent. The remaining solid plant matter is filtered away and the liquid solvent and cannabinoid mixture is purged to remove all solvents, leaving the cannabinoids and other active compounds from the plant.
While no solvent is perfect for cannabis extraction in every way, butane extracts and supercritical CO2 extracts account for the production of a vast majority of currently available concentrates. Butane is non-polar, which allows extraction of the desired cannabinoids and terpenes from cannabis without the co-extraction of undesirables (like chlorophyll and plant metabolites). The low boiling point of butane makes it easy to purge from the concentrate at the end of the extraction process. However, butane is highly combustible. While supercritical CO2 has been praised for its relative safety in terms of toxicity as well as for its low environmental impact, a lengthy purification process will be required to remove co-extracted constituents (e.g. plant waxes) that can detract from the final cannabinoid and terpenoid profile of supercritical CO2 extracts. Ethanol can be as effective as CO2, as efficient as butane, can be safe to handle, and is Generally Regarded as Safe, or GRAS. Because ethanol is a polar solvent, it will mix with water and will dissolve water-soluble molecules like chlorophyll.
Extraction methods with non-hydrocarbons
Dry Sieve is the most naturally and unobtrusive form of cannabis extraction. It has a low yield due to the meticulous process involved in removing the cannabinoid containing trichomes from the plant matter. There are many grades of dry sieve from a farmer sieve containing plant contaminant, to what is often referred to as kief (a mixture of glandular trichome heads, stalks, and plant material), up to Fullmelt Dry Sieve which generally contains just the trichome heads. There are multiple ways to achieve dry sieved products, but a single silk screen or a series of silk screens can be utilized in conjunction with agitation to separate trichomes from the plant material.
Water extraction is very much like the dry sieve process. It can be used in conjunction with screens to carry mechanically separated trichomes through multiple micron level screens. Water hash is made using agitation to gently break off the trichome heads from the plant material.
CO2 is arguably the least-toxic form of cannabis concentrate extraction, CO2 (carbon dioxide) has become more popular as an extraction method because of its low environmental impact and non-existent toxicity. However, CO2 extraction systems are considerably more expensive than butane or hexane systems. CO2 functions as a solvent when it is heated or cooled and pushed through the flower at high (supercritical) or lower (subcritical) pressures. The majority of the cannabis CO2 extractions are done in the subcritical phase. Subcritical CO2 extraction gives a lighter coloured extract (fewer waxes and resins), and retains significantly more volatile oils compared to supercritical CO2 extraction. However, creating quality CO2 extracted concentrates is incredibly difficult without the proper equipment rated for the appropriate pressures. Carbon dioxide is a gas at standard temperatures and pressure. It forms a liquid at pressures above 73psi, and its critical point is 33.1oC. Many plant waxes and fatty acids are soluble in supercritical carbon dioxide, and these need to be removed by winterization during the refinement process.
Extraction methods with hydrocarbons.
Butane & Propane. Hydrocarbon extraction is the fresh-squeezed juice of the concentrate world. Hydrocarbons (butane and propane) are arguably the most efficient solvent for cannabis extraction. Butane is a low-pressure system where extractions occur at 0-30psi. The most commonly used solvent in cannabis extraction is butane. Butane has a low boiling point (-0.5°C), which is helpful when cold-boiling the residual solvent from the concentrate solution. This process leaves behind the temperature-sensitive terpenes. Many extraction technicians prefer to blend their butane with propane to create a gas mixture that will strip additional terpenes and purge more efficiently than butane alone. The boiling point of propane is -42°C. These solvents are non-toxic, non-polar and they dissolve oils very efficiently without creating other unwanted by-products. Butane and propane dissolve all cannabinoids and terpenes. These solvents are cost-effective, meaning large amounts of money are not spent on supplies for extraction, but instead on growing quality cannabis to be extracted. Butane and propane purging following concentrate extraction is comparatively easy because of their lower than room temperature boiling points. Hydrocarbon extraction should only be done in a proper lab setting. Butane is flammable and there is the lack of automated options (like CO2 and ethanol systems). Automated hydrocarbon extraction systems will improve in quality and decrease in price as their safety features and internal monitoring systems become more reliable. Butane extracts do not usually need to be winterized and filtered because little chlorophyll and lipids/waxes are extracted at the low temperatures used.
Hexane. Like butane, hexane is a solvent that can be used for cannabis concentrate extraction. Hexane is completely insoluble in water, but it boils at a higher temperature than butane. Although the general process for hexane extraction is similar to that of butane extraction, it requires significantly more care due to the fact that hexane is considerably more toxic, extremely flammable and potentially explosive.
Acetone. Easily available as a solvent and degreaser, acetone evaporates rapidly and it is a popular solvent and is recognized to have low acute and chronic toxicity if ingested or inhaled. Acetone has been internationally rated as a GRAS (Generally Recognized as Safe) substance for food use and is produced and disposed of in the human body through normal metabolic processes. Acetone has a boiling point of 57°C. The most hazardous property of acetone is its extreme flammability (flash point is -20°C).
Isopropyl Alcohol. Isopropyl alcohol is a commonly used solvent for creating cannabis concentrates using a quick washmethod. Where hexane is not water-soluble, isopropyl alcohol is highly water-soluble and will dissolve undesired plant materials (chlorophylls and waxes) along with the sought-after cannabinoids. QWISO (Quick Wash Isopropyl) typically requires under a minute to produce a very high-quality oil. In order to eliminate plant waxes from the isopropyl concentrate solution, a quick wash method is used as opposed to soaking (which is used with non-water soluble solvents like hexane). It takes significantly longer to properly purge concentrates extracted with isopropyl alcohol due to the solubility in water.
Ethanol. Ethanol extraction can be conducted under warm or cold conditions. An example of a warm ethanol extraction processes is the Soxhlet technique. This technique essentially boils ethanol in a flask, condenses the alcohol, which then drips through the packed flower material, stripping the cannabinoids and terpenes during the process. The advantage to this approach is that the extraction is time efficient with a relatively low solvent-to-feed ratio. Because the warm-ethanol extraction technique generally extracts chlorophyll/waxes and decarboxylates the cannabinoids (due to the heat involved), additional dewaxing and clarification steps are usually required. The warm ethanol extraction processes can only generate a limited number of products because any acid-form cannabinoids are decarboxylated during the extraction. Using ethanol under cooler conditions allows terpenes and acid cannabinoids to be efficiently extracted. The literature suggests that cannabinoids are soluble in ethanol at a 1:1 ratio (meaning that 1g of THC is soluble in 1mL of ethanol). Ethanol cannot be tailored to separate cannabinoids or terpenes during the extraction phase to work into a predetermined product pipeline. Overall, ethanol extraction is an effective process most suited to high-throughput, bulk-processing laboratories that focus on a few products.
Author Dr. Craig Davis