Cannabidiol (\(\text{CBD}\)) is a naturally occurring compound found in the Cannabis sativa plant. It is one of over a hundred phytocannabinoids. The \(\text{CBD}\) used in consumer products is extracted from industrial hemp, a variety of Cannabis sativa legally defined as containing less than \(0.3\%\) of the psychoactive compound \(\text{THC}\) by dry weight.
\(\text{CBD}\) resides within the plant’s resin, concentrated in microscopic glands called trichomes, primarily on the flowers and surrounding leaves. Since the compound is locked within this raw plant material, a precise chemical process is needed to separate the desirable compounds from the bulky plant matter. Extraction concentrates the \(\text{CBD}\) into a usable oil or isolate form, allowing for the formulation of tinctures, capsules, edibles, and topical products.
Preparing Hemp for Processing
The journey of \(\text{CBD}\) begins with preparing the raw plant material, or biomass. Industrial hemp is cultivated for high cannabinoid concentration in the flowers and leaves. Once mature, plants are harvested and must undergo thorough drying and curing.
Removing moisture is necessary because excess water interferes with solvent efficiency during extraction and increases the risk of mold during storage. The harvested material is dried until its moisture content is below \(10\%\). This preparation ensures the stability of the biomass before processing.
Before extraction, the dried biomass is typically milled or ground into a coarse powder. This mechanical reduction increases the total surface area exposed to the chosen solvent. Maximizing the surface area achieves a high extraction yield, allowing the solvent to efficiently penetrate the trichomes and dissolve the cannabinoids.
Industrial Scale Extraction Techniques
Once the hemp is prepared, industrial processors employ various methods to wash the cannabinoids and other compounds away from the plant matter. These techniques are selected based on factors like cost, safety, scalability, and the desired quality of the final extract. The result of any initial extraction method is a highly concentrated, dark, viscous substance known as crude oil.
Supercritical \(\text{CO}_2\) Extraction
Supercritical \(\text{CO}_2\) extraction is a favored method for producing high-quality \(\text{CBD}\) oil. This process uses carbon dioxide brought to a state above its critical temperature and pressure. In this “supercritical” state, \(\text{CO}_2\) acts like both a gas and a liquid, allowing it to diffuse through the hemp biomass while dissolving compounds.
The \(\text{CO}_2\) acts as a “tunable” solvent because small adjustments to the temperature and pressure can precisely target specific compounds, such as \(\text{CBD}\) or terpenes, while leaving behind unwanted materials like chlorophyll. After the supercritical \(\text{CO}_2\) passes through the hemp, it carries the extracted compounds into a separator chamber. The pressure is then released, causing the \(\text{CO}_2\) to revert to its gaseous state and evaporate completely, leaving behind a solvent-free crude oil.
Ethanol Extraction
Ethanol extraction is a widely used method, valued for its low equipment cost and high throughput, making it suitable for large-scale operations. This technique uses food-grade ethanol, a polar solvent, to wash cannabinoids and other compounds from the ground hemp material. The biomass is typically soaked in chilled ethanol to dissolve the resinous material.
Cold ethanol, often used at temperatures as low as \(-40^\circ\text{C}\), is preferred to reduce the co-extraction of undesirable polar compounds like chlorophyll. Chlorophyll can impart a bitter taste and dark color to the final product. Ethanol is a highly efficient solvent that dissolves a broad spectrum of compounds, including waxes and lipids. After soaking and filtration, the ethanol is removed from the solution using specialized evaporators, leaving behind the crude \(\text{CBD}\) oil.
Hydrocarbon and Oil Extraction
Hydrocarbon solvents, such as butane and propane, are used in some extraction processes, though less commonly for high-purity \(\text{CBD}\) production than \(\text{CO}_2\) or ethanol. These non-polar solvents efficiently dissolve cannabinoids and terpenes but require rigorous safety protocols due to flammability. The solvent is typically evaporated off at low temperatures, resulting in a potent extract.
Simpler oil extraction methods, utilizing common cooking oils like olive oil or coconut oil, are sometimes used on a small scale. In this process, the hemp is heated to activate the cannabinoids before being infused into the oil. While these methods are simple and safe, they are not scalable for industrial production because the resulting oil is less concentrated and the solvent cannot be easily removed, limiting its use in many product types.
Post-Extraction Purification Steps
The crude oil contains a mix of cannabinoids, waxes, fats, and residual solvents. To create a clean, consumer-ready product, the crude oil must undergo several purification and refinement processes. These steps determine whether the final product will be a full-spectrum extract, a broad-spectrum extract, or a pure \(\text{CBD}\) isolate.
Decarboxylation
Decarboxylation is the first common refinement step, converting non-activated cannabinoid acids into their neutral, active forms through heating. In raw hemp, \(\text{CBD}\) exists primarily as cannabidiolic acid (\(\text{CBDa}\)), which contains a carboxyl group. Heating the crude oil, typically between \(100^\circ\text{C}\) and \(140^\circ\text{C}\), removes this carboxyl group as carbon dioxide and converts \(\text{CBDa}\) into the \(\text{CBD}\) compound.
Winterization
Winterization removes undesirable plant waxes, lipids, and fats co-extracted with the cannabinoids. The crude oil is mixed with a solvent, usually ethanol, and chilled to extremely cold temperatures, often below \(-20^\circ\text{C}\). At these low temperatures, the waxes and fats solidify and precipitate out of the solution.
The chilled mixture is then passed through a series of filters, which physically separate the solidified impurities from the cannabinoid-rich liquid. Once filtered, the remaining ethanol is removed from the solution using evaporation, leaving behind a dewaxed and cleaner oil. This step is particularly important for products intended for vaporization, as waxes can be harsh when inhaled.
Distillation and Isolation
For a higher-purity product, the oil proceeds to distillation, which separates compounds based on their boiling points under vacuum pressure. Specialized equipment, like a wiped-film evaporator, heats the oil, causing different compounds to vaporize at different temperatures. The vapors are collected separately, resulting in a highly concentrated extract that can reach \(80\%\) to \(90\%\) total cannabinoid content.
Further purification leads to \(\text{CBD}\) isolate, the purest form of the compound. This involves dissolving the distilled oil in a solvent and creating specific conditions, such as cooling or stirring, to encourage \(\text{CBD}\) molecules to crystallize. The resulting crystals are washed and dried, yielding a white, odorless powder that is \(99\%\) or more pure \(\text{CBD}\).