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The Process of Cannabis Purification

By Alexander Beadle

Published: Apr 25, 2023   
A gloved hand pours oil out of a beaker.

Image credit: iStock

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The cannabis extract market is already worth more than three billion USD and is projected to bring in more than 15 billion USD in revenue annually by 2023. But as an influx of new producers and new products come into the space looking to capitalize on this growth, the importance of proper processing and purification from a consumer safety standpoint is clear.

Even for established, vertically integrated companies, the variation between different harvests or individual plants can demand a rigorous and flexible post-processing procedure in order to make sure that the final product is as precise, accurate, and safe as possible.

In a recent Analytical Cannabis webinar, Sabrina Didado, founder and owner of Cosmic Harvest Hemp, outlined the current solutions being used for cannabis oil purification at the industrial scale.

Purification begins with planting and extraction

It may sound counterintuitive at first, but the cannabis purification process really begins long before there is a cannabis oil ready to be purified.

“Before thinking about any type of extraction or production, the starting material must be taken into consideration,” Didado said. “The water in the environment plays an important role when talking about product purification. The type of material, whether you’re starting with flower or trim, the variety or strain of the plant, the cannabinoid concentration, terpene profile, moisture content, the overall cleanliness of the flower, and so on is important when thinking about the end product.”

As Didado explained, cannabis purification means ensuring that all final products are free from contaminants that could pose a risk to consumers. This means testing the starting product for impurities, such as pesticides or microbial risks.

It also means thinking closely about the extraction method that is being used. Different extraction methods will have different extraction efficiencies, which will be of great importance to producers looking to make extremely high-purity cannabinoid isolates. But regardless of whether the final product is an isolate or a more broad-spectrum oil, using standard operating procedures and ensuring a sanitary laboratory environment will help to guard against excessive residual solvents or other sources of contamination that will require aggressive purification and clean-up.

Cannabis filtration

Filtration is normally the first purification step that is carried out on a product, immediately after the primary extraction has been completed. Using a variety of filter media, filtration ensures the final cannabis oil produced is free of any contaminants that might affect the oil’s color, clarity, or purity.

Winterization is a key process for many operators looking to create refined and pure cannabis oil. By mixing the non-polar crude cannabis oil with a polar solvent (such as ethanol) at sub-zero temperatures, the undesirable plant waxes, lipids, and fats will be pulled away from the crude oil and coagulate to form a solid layer at the top of the mixture. Vacuum-assisted filtration is then used to separate these undesirable waxy solids from the rest of the mixture. The winterization process can be repeated as many times as needed to fully dewax the oil before the ethanol solvent is evaporated off.

Many producers also choose to scrub the oil with media such as activated carbon or bleached clay as a final finishing step in the filtration process, which can help to remove unwanted sugars and pigments such as chlorophyll.

The wider purification process

To illustrate how cannabis purification occurs at the industrial scale, Didado outlined a hypothetical purification process that might be used by an extractor who is wanting to produce crystalline THC isolate for the medical market.

Starting with harvested flower, the processor would use a primary extraction technique to produce the cannabis oil. In this example, Didado considered a supercritical CO2 extraction process that yields an oil containing around 60% delta-9 THC. After the extraction step, winterization and filtering are done to remove the various plant waxes and natural impurities.

“This yields refined oil at around 75% delta-9 THC,” Didado said. But to turn this clean oil into the desired cannabinoid isolate, even more post-processing purification is needed.

“From here, distillation is performed, yielding a distillate at around 85% delta-9 THC. This distillate is then washed with a solvent to dissolve the delta-9 THC, and from there it’s chilled and crystallization of the delta-9 THC starts,” she continued.

After some additional washing and drying steps, this process will yield the desired pure isolate containing upwards of 97% delta-9 THC. But the process for a broad-spectrum oil or another product will look different.

“This is a multi-step process, as mentioned before, depending on the desired material. And while performing the separation, it’s imperative that no outside contaminants or substances interfere, this will obviously alter the purity of the substance,” Didado said. “Proper sanitation and cleanliness measures must be taken place at all times in your facility.”

Purification for terpene extracts

The versatility of purification is also highlighted by how producers deal with terpene extracts. Due to their volatility, these compounds are usually extracted from raw material before the cannabinoids are. Many producers will choose to capture these terpenes with the intent of re-introducing them back into a clean cannabis oil so that some of cannabis’ distinct flavors and aromas are maintained.

“The most common impurity and terpene collection and extraction is water,” Didado said. “This can be fixed by using a liquid separation funnel, or if you are in a more large-scale production facility, you can use a drying agent, or freezing, or burning to remove any of these impurities.”

Regardless of what is being isolated and purified, Didado recommends that cannabis products undertake a full panel of testing at least twice during production — once on the raw material before any processing takes place, and once on the finished product. This is a legally mandated minimum in some regions. Didado also suggests that producers could add third-party checks on the soil and plant material pre-harvest and on the cannabis oil post-extraction, in order to identify any contaminants that must be addressed during purification. 

Alexander Beadle

Science Writer

Alexander Beadle has been working as a freelance science writer since 2017 and has covered the cannabis industry for Analytical Cannabis since 2018. He has also written for our sister publication, Technology Networks, and the cannabis industry consultant firm Prohibition Partners, among others. Alexander holds a Master's in Materials Chemistry from the University of St. Andrews, where he won a Chemistry Purdie scholarship, and conducted research into zeolite crystal growth mechanisms and the action of single-molecule transistors.


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