The goal of cannabis extraction is to create a product with a high concentration of cannabinoids. Simple, right? In reality, getting cannabinoids like THC and CBD from Point A, where they’re inside the plant, to Point B, where they’re in a concentrated form is a highly technical process. Keep in mind that it requires properly engineered equipment and highly knowledgeable, skilled experts. This is high-level chemistry, not cooking. Any extraction process must be executed correctly to produce an end-product safe for human consumption—and the results should always be tested and confirmed by an independent third-party laboratory.
In laymen's terms? Think of a molecule like a lock and a solvent like a key; you want to find the perfect key.
Supercritical CO2 Extraction
Carbon dioxide, or CO2, is a gas found in the atmosphere. In order to create a solvent, it must undergo something called a “supercritical” phase. This means that you must compress and heat this gas in order to change it into a liquid form—that’s why the process is called a supercritical CO2 extraction.
This technology is not unique to cannabis extraction, but has been around for years as a standard extraction method for food. It’s used to produce carbonated soft drinks, as well as to remove caffeine from coffee beans in order to make decaf coffee. As the cannabis industry began to scale globally nearly 10 years ago, scientists repurposed supercritical CO2 into the industry.
Because of the recent boom in the hemp industry, this method of extraction is now the most common and advised way of extracting CBD from hemp. For CBD extraction, it is considered the gold standard, because carbon dioxide is a non-toxic substance that doesn’t leave any residue behind, a safety imperative when consuming any CBD product.
Compared to other solvents (such as ethanol) carbon dioxide isn’t the most effective solvent to extract the cannabinoids. Cannabinoid structures are contained within the plant’s trichomes—the mushroom-like “hair” shape on the outside of leaves of the plant that contain all the cannabinoids, terpenes, and flavonoids. The purpose with any of the solvents is to dissolve the trichome structure and isolate those molecules. Supercritical CO2 is less effective than some of the other solvents.
Remember our lock and key analogy?
Carbon dioxide isn’t the best key. In fact, it’s a bit like jamming a screwdriver into the lock. It’s going to work, but it requires a lot more patience and dexterity. Effectively, you are passing a solvent (CO2) that does not have the best solubility with the trichome structure of the plant, which means that it needs to be repeatedly passed over the trichome structure to extract all the cannabinoids, terpenes, and flavonoids. This is more time-consuming than other solvents and can take several hours.
At atmospheric temperature, CO2 is a gas. Liquid CO2 cannot exist at atmospheric pressure, and as mentioned earlier, it has to be heated to reach the supercritical phase. This means that liquid CO2 is at a higher pressure than CO2 in its gas form. Because we are pouring this liquid CO2 over plant matter, we are working with much higher base psi, or the amount of force expressed in pounds of force per square inch.
When it comes to CO2 extraction, you need equipment that is going to be able to withstand pressures of anything from 1500 to 5000 psi, specifically engineered to withstand the demands of large scale extraction. Aspects of the equipment such as shell thickness, valves, nuts, and bolts need to be tested and proven to withstand high pressure. Because of the high cost of this equipment, extracts produced by this method are more expensive than other solvent-based extractions.
Hydrocarbon Extraction: Butane & Propane
We want to find the perfect key to unlock all our molecules. When it comes to cannabis extraction, we have not found a better key than butane and propane. These are both non-polar solvents with a low boiling point, meaning that they are going to bind to all your cannabinoids, terpenes, and other desirable aspects of the plant. This is why end-products such as shatter have a beautiful vivid golden color and a rich terpene smell. Live resin, budder, and wax are also concentrate-types used to describe different textures, and they are all products of hydrocarbon extraction. Using butane and propane, you can make many different types of products.
Although hydrocarbon extractions pull the best terpene and cannabinoid profiles out of the plant, they also present a couple of issues. They are the most flammable solvents—more flammable than ethanol and carbon and require a high pressure (though not as high as CO2) meaning there is a cost to engineer the right equipment. With CO2, pressure rates reach as high 5000psi, whereas with butane and propane pressure rates tend to be between 50-150psi. Because of this, hydrocarbon extractions present a safer work environment than CO2.
For extraction on a larger scale, hydrocarbon is very costly and difficult to engineer. It’s not really feasible for large scale hemp extraction, so most extraction facilities process hemp using the CO2 method. This is also why we have seen more facilities move towards ethanol.
Alcohol Extraction: Ethanol
From a chemical standpoint, ethanol is a great key to unlock the cannabinoids, but it is an extremely polar solvent. It binds to the cannabinoids and terpenes in the same way hydrocarbons do, but will also bind to undesirable compounds within the plant, like chlorophyll.
In order to bypass this, extractors can chill the ethanol and bypass the undesirable matter, but to chill the ethanol on a larger scale is expensive and requires properly engineered equipment. Factors like mass balance and post-processing procedures need to be considered. It is far more complex than simply pouring ethanol over plant matter, and you need a thorough understanding of how cooling the solving will impact a number of different variables along the process. Due to a lack of regulation, individuals with a lack of understanding of how ethanol interacts with other compounds are extracting cannabis, creating an end-product left with harmful contaminants that can have adverse effects on an individual’s health. Processing at scale with ethanol can be done, but you need a strong team of experts that understand how to navigate these variables.
From a fundamental standpoint of scaled extraction, ethanol is less flammable than hydrocarbons, doesn’t need to be pressurized like CO2 and customers are familiar with ethanol. However, if ethanol extraction is done incorrectly, it can have some of the most damaging health effects due to contaminants.
Ultimately there are not right or wrong ways to extract cannabis, but any extraction process must be properly executed by a team of experts and tested to ensure the end-product is fit to ingest.
Cannabis Extraction 101
Common terms to know.
Solvent: something able to dissolve other substances
Molecule: a particle made up of two or more atoms that are chemically bonded
Trichome: the fine outgrowths or appendages on plants.
PSI: a metric used in chemistry when describing the amount of pressure expressed in pounds of force per square inch.
Polar solvent: a polar solvent is a liquid with molecules that have a slight electrical charge due to its shape