The process by which cannabinoids and terpenes found within cannabis are recovered from the plant material. There are a variety of machines, solvents, and techniques that can be utilized to extract cannabis compounds.
I prefer concentrates made using mechanical separation, as no solvents are used during the process.
My favorite wax is made using a chemical extraction technique that utilizes supercritical CO2.
Mechanical Separation vs. Chemical Extraction
Extraction of cannabis components can be performed using either a mechanical (physical separation) or chemical (solvent extraction) process. The physical separation has historically been used in India and the Middle East to make hashish, while solvent extraction was introduced in the late 19th century by North American pharmaceutical companies in order to make reproducible doses of cannabis extracts. Parke, Davis and Co., now owned by Pfizer, developed a cannabis fluid extract in 1896 that stayed on its physicians' catalog until 1937.
The mechanical extraction process employs pressure and/or physical action to remove the whole trichome. Chemical extractions differ by utilizing a chemical solvent to dissolve the trichomes from the plant.
Mechanical separation methods use centrifugal action, gravity separation, and filtration to separate the trichome glands from the plants. The most common methods are the following:
- Sieving the ground plant by hand or in a mechanical tumbler composed of screens delicately removes the exposed trichomes, resulting in a powder called kief. Kief can be smoked or vaped either on its own or mixed with flower in a bowl, joint, or bong. Kief can also be further refined using the below warm press method or pressed into hashish for long-term storage.
- The Ice-water method, in which plant material, ice, and water are combined in a vessel and agitated until the trichome glands break off the plant and sink to the bottom. This method often results in what's known as bubble hash, which, in line with its name, bubbles when burned. Like kief, ice-water hash can be smoked on its own or with flower. Particularly high-quality hash can also be dabbed, while lower-quality hash can also be pressed using the below method.
- Cold and warm press methods, known as making rosin, use heat and pressure to remove the cannabinoids and terpenes from the plant. Very similar to an oil press, heat and pressure are applied (upwards of 40,000 lbs. of force) to the plant material until the resin glands are excreted from the plant material. Rosin is primarily dabbed or consumed using a dab pen.
Most mechanical methods are inexpensive to set up and operate, but a rosin press can be costly. These methods often lack the efficiencies required for commercial-scale production. The greatest hazard in mechanical separation comes into play when dry-ice (frozen carbon dioxide, or CO2) is used to create kief. If using the dry-ice method, exercise caution to avoid freezer burns.
Solvent-based extractions are the most efficient methods in removing trichomes from the cannabis plant and are the preferred method for the commercial cannabis industry. Trichome glands are non-polar compounds and therefore require a non-polar solvent to remove them from the plant. The main solvents employed are butane, propane, ethanol, and supercritical carbon dioxide.
While these solvents are toxic, flammable, and asphyxiants, they are generally recognized as safe (GRAS) by the U.S. Food and Drug Administration (FDA) and have been used in the pharmaceutical and food industry for decades. With the proper lab design of a closed-loop system, and with engineering and administrative controls in place, the chemicals can be used safely for extraction.
Solvents are used in liquid form to essentially “wash” the plant of its therapeutic compounds, after which the solvent must be removed from the solution before it is safe to consume. Processors seek solvents that have extremely low boiling points in order to maintain the full spectrum of compounds removed without denaturing or boiling them off during the process of removing the solvent from the solution.
Solvent-based extractions typically take place under relatively low pressures (15 to150 pounds of pressure per square inch, or PSI) and temperatures (-40 to -70 degrees Fahrenheit, or -40 to -56.67 degrees Celsius), but new methods, using supercritical fluids, utilize much higher pressures (1,000 to 9,000 PSI) and temperatures (35 to 215 degrees Fahrenheit, or 1.67 to 101.67 degrees Celsius) to dissolve the essential compounds.
Supercritical Fluid Extraction (SFE)
Supercritical fluid extraction (SFE) utilizes a fluid that has been heated and pressurized above its critical point, where it exhibits both gas and liquid properties. In this phase, the liquid's solubility increases, which allows it to move through the plant material like a gas, but dissolve trichomes like a liquid. Due to its relative low-cost and availability, supercritical carbon dioxide (CO2), has been the preferred solvent for SFE products.
Types of Chemicals
There are several types of solvents and chemicals that work for extracting cannabis properties, with varying efficiency and productivity. If the goal is to strip all cannabis compounds from the trichomes, a light petroleum gas-based solvent such as butane is preferred. CO2, on the other hand, is a selective solvent and is utilized for extracting selective compounds like terpenes and certain cannabinoids. When CO2 is repeatedly passed through plant material in a closed-loop system, it gradually gets to all of the cannabinoids.
Ethanol and propane are often used in industrial-sized extraction systems and each of the aforementioned solvents and chemicals basically does the same thing, but based on their natural properties, you may want to use one over the other. When setting up a chemical or solvent-based extraction system, be sure to do your research and choose the extractor best suited to your needs.
It's a matter of personal preference if plant material is milled, or ground, prior to being loaded into the material column. After the material column contains the cannabis, a vacuum pump removes all oxygen from the system. The solvent column is then chilled to -40 degrees Fahrenheit (also -40 degrees Celsius) and the material is soaked with a liquid solvent. Once the solvent is reclaimed with the cannabis compounds extracted, the residual solvent is removed via a vacuum oven under enough heat to return it to gas form. The solvent then travels back to its original column, creating the loop in a closed-loop system.
- Cured Nugs: Because cannabis nugs hold the greatest concentration of trichomes over the rest of the plant material, cured nugs create what's known as “nug run” concentrates. Nug run extractions vary from shatter to budder to sauce and have greater aromas, flavors, and more potent effects than when cannabis trim is utilized.
- Trim: Made up of trimmed plant material, usually greatly consisting of the sugar leaves that cup the buds, trim run concentrates will have fewer terpenes and cannabinoids than nug run or live resin extracts.
- Live resin: – When creating what's known as live resin, extractors must freeze a freshly chopped plant right away, either using liquid nitrogen or a freezer. Once the material is fully frozen, its essential properties are extracted. This method is highly rated for its preservation of aromatic, flavorful terpenes and produces the most potent, aromatic concentrates available on the market.