how do they remove thc from cbd oil

December 15, 2021 By admin Off

Curing is the final post-harvest procedure that allows for the development of the maximum flavor in the cannabis plant (Vogel 2018). Jin et al. (2019) believed that the best temperature and humidity for curing are at 18 °C and 60% RH for 14 days. Green et al. (2018) suggested keeping the trimmed flowers in a can for up to 4 weeks in a dark cupboard while opening the lid every day for about 6 h is the best method for curing (Jin and Chen 2019). At temperatures between 15–21 °C and 45–55% humidity, enzymes and aerobic bacteria will be in the optimum condition to breakdown undesired sugars and degrade minerals. Curing can reduce the harsh smell and the sense of throat burning during smoking or vaping as well as increasing the shelf life by minimizing mold growth. It is also believed that curing can increase cannabis potency as the number of cannabinoids such as THC and CBN will increase by curing. Although curing is one of the most significant post-harvest stages for the cannabis plant, there are not enough academic investigations around this area.

Dynamic maceration is a conventional solid-lipid extraction procedure that is based on soaking a sample in organic solvents (solvent varies depending on the polarity of the target compound) for a specific time at a specific temperature and followed by agitation (Fathordoobady et al. 2019). This process of separation is inexpensive and a popular method used to obtain essential oils and bioactive compounds (Azmir et al. 2013). Recently, the use of vegetable oils (e.g., olive oil) as maceration extraction solvents was found to be more useful for extracting higher amounts of terpenes than alcoholic solvents, notably when using extended heating time. However, vegetable oils are not volatile and are difficult to remove from extracted isolates (Romano and Hazekamp 2013). Alternatively, ethanol is suggested as a preferred solvent for cannabinoid extraction. A study conducted by Fathordoobady et al. (2019) demonstrated that there was no significant difference between other organic solvents (n-hexane, acetone, methanol) and ethanol when used for neutral cannabinoid recovery. However, when the recovery of acidic cannabinoids was tested, ethanol had the highest yield. The use of ethanol for maceration extraction of cannabinoids was found to produce the highest yield when used twice compared to other methods of extractions, for instance, ultrasonic-assisted extraction (UAE) or supercritical fluid extraction (SFE) (Fathordoobady et al. 2019).

In all the drying methods mentioned above, humidity, temperature, ventilation rate, and time are the most important parameters to be optimized. Incorrect drying conditions may cause decarboxylation of acidic cannabinoids and loss of terpenes. The presence of light, oxygen, and heat may also cause degradation in cannabinoids and terpenes and can affect the taste (Jin and Chen 2019).


The focus of this narrative review was on Cannabis sativa , initially where 93 papers were identified. Papers on various drying and extraction methods specifically for Cannabis sativa L. were included while those for using hemp as fiber and protein sources were excluded. Overall, 12 papers about cannabis seed oil, hemp seed oil, or hemp plant were excluded as this review focuses on the oil coming from flowers. In the end, 81 related papers about various drying, extraction, and post-harvest processes were carefully reviewed.

This is a narrative review paper which focuses on critiquing drying and extraction methods of Cannabis sativa L. plant. Relevant keywords such as medicinal cannabis, extraction, solvent, cannabinoids, and terpenes have been searched in PubMed, EMBASE, MEDLINE, Google Scholar, and Cochrane Library (Wiley) databases.

Romano and Hazekamp (2013) compared five different solvents (naphtha, petroleum ether, ethanol, olive oil + water, and olive oil) using DM (Table 3). Except for naphtha, other extracts contained a small amount of THC and THCA around 5–10%. Naphtha was an exception which had 33% THC plus THCA. With ethanol as solvent, unwanted chlorophyll was extracted along with the cannabinoids. The unwanted chlorophyll not only added an unpleasant flavor and a green tinge to the end product, but it also demonstrated accounts of interference with gas chromatography–mass spectrometry analysis, hence removal is considered necessary (Ciolino et al. 2018). To eliminate unwanted chlorophyll, the ethanol extract can be treated with activated charcoal. However, the use of activated charcoal can result in the reduction of cannabinoid content by approximately 50%. Consequently, although yields are high with ethanol, the removal of unwanted chlorophyll with charcoal comes at the expense of cannabinoid loss. In respect of toxicity, Romano and Hazekamp (2013) found significant amounts of petroleum hydrocarbon residues in the extracts obtained with naphtha and petroleum ether, indicating that special attention must be paid to ensure safe residual concentrations (Romano and Hazekamp 2013).

Hydrodynamic cannabis extraction is a recent development within the cannabis industry that can be used to produce full-spectrum cannabis extracts with high bioavailability. There have been accounts of companies, such as IASO (Incline Village, Nevada), claiming to have developed a unique extraction system that produces products with high yield and increased potency. This alternative method involves freezing fresh plant material and converting it into a nanoemulsion in water by ultrasonication. Hydrodynamic force is then used to break the cell wall and release its contents. This is followed by liquid–liquid extraction using solvents, centrifugal separation, and finally low-temperature drying. The initial step of freezing the plant matter helps preserve the volatile compounds as well as acidic cannabinoids during the following steps. Hydrodynamic extraction is claimed to exceed conventional methods mainly due to the lack of high temperatures, short contact distillation, and low organic solvent consumption (admin, n.d.). Ishida and Chapman (2012) used this technique to extract carotenoids from tomatoes and found that the extractable lycopene, other carotenoids, and accessibility of carotenoids significantly improved (Ishida and Chapman 2012). However, to this date, there has been no scientific publication that explores this method of extraction. Therefore, to fully understand the efficacy of this method, more research is required.

Vegetable oils composition by fatty acid profile, inspired by Yara-Varón et al. (2017)

In common with other solvents, CO 2 —which is nominally a polar gas—enters a so-called supercritical state at a defined temperature and pressure. In a supercritical state, distinct liquid and gas phases do not exist. In the case of CO 2 , the critical temperature is 31.06 °C, the critical pressure is 73.83 bar, and the critical density is 0.460 g/cm 3 (Raventós et al. 2002). Supercritical CO 2 behaves like a non-polar solvent, capable of extracting a broad range of non-polar solutes, cannabinoids included. In comparison, strongly polar water becomes supercritical and useful as a non-polar solvent but at a much higher temperature and pressure, 647 K and 22.1 MPa (Fig. 3). Therefore, CO 2 is the solvent of choice due to low critical temperature and pressure. It is also non-flammable, non-toxic, inert, renewable, easy to remove, abundant, and relatively low-cost. As an example, consider supercritical extraction of linalyl acetate from lavender oil compared with its extraction by conventional steam distillation (Reverchon et al. 1995). The yields for supercritical extraction were 34.7% compared with 12.1% for the conventional steam distillation. The reason proposed was that the higher temperature of steam distillation caused the undesirable hydrolysis of the linalyl acetate to linalool and acetic acid.

The differing solubilities of individual cannabinoids and other phytochemicals are thought to be an important factor that needs to be considered when selecting a solvent. The stickiness and viscosity of cannabis oil result in binding to solvents; therefore, it is important to consider the toxicity, affinity, and temperature profile of the solvents being used (Fathordoobady et al. 2019). The efficiency of conventional methods of extraction is presented to be heavily dependent on the solvent of choice. Solubility, molecular affinity, mass transfer, co-solvent, toxicity, and environmental safety are major factors that should also be considered during the solvent selection process (Azmir et al. 2013). Commonly used solvents to extract cannabis can be divided into three groups, low molecular mass organic solvents, vegetable fats (oils), and supercritical fluids, notably supercritical carbon dioxide (Reichardt and Welton 2011).

Soxhlet extraction.

As the cannabis industry transitions from a black market to a legal market, product development, and methods of extraction have become a focal point. To date, more than thousands of chemical constituents have been identified from the cannabis plant, all of which possess different chemical properties that require different conditions for preservation during drying and extraction. However, scientific publications that explore these areas for the cannabis plant are currently lacking.

Air-drying (hang-drying) of the cannabis plant.

Long-established solventless methods such as dry-sieving, water extraction, and rosin press extraction lack coverage in literature due to outdated techniques and difficulty in scaling despite having simple procedures. Dry sieve extraction produces a powder-like Kief with a potency of approximately 35–50% THC. The process of dry-sieving begins by beating dried cannabis against a mesh screen and forcing the trichomes to separate and fall off. The final product can either be pressed further into hashish or mixed with dried flowers. This simple procedure is time-consuming and labor-intensive, therefore, not popular for the industrial level. Water extraction produces roughly the same potency of THC as the dry sieve method, although it also depends on the potency of the starting material. The procedure begins by placing the cannabis plant in a mesh bag immersing it in ice water and finally stirring it to knock the trichome off. The trichome is further filtered through a series of screens then allowed to settle before collecting and drying the final product, commonly known as water hash or bubble hash. Similarly, to dry sieving, this process is difficult to upscale as well as limited control of potency (Blake and Nahtigal 2019).

Olive oil is a well-known solvent in the cannabis extraction field. It is also one of the least refined oils with characteristically high oleic acid content. Terpenes can be preserved during extraction with olive oil due to their low volatile nature. Romano and Hazekamp (2013) used two different protocols with olive oil for cannabis extraction. In the first experiment, 5 g cannabis with 20 ml olive oil and 50 ml water were mixed and heated up to 60 min. In the second experiment, 10 g cannabis with 100 ml olive oil were mixed and heated for up to 120 min. The extract concentration to the solvent ratio for the first and second protocols was 5 g/20 ml and 10 g/100 ml, respectively. The high yield of terpenes obtained from using olive oil as a solvent is thought to be due to its efficient capabilities in solubilizing and limiting loss of product by protecting the compounds from evaporation (Romano and Hazekamp 2013).

MAE process where the flask is housed in the microwave oven (Krishnan and Rajan 2017). Placing the flask containing the sample in the microwave, attached to a condenser outside of microwave to capture the solution of interest compounds after distillation.

Air-drying, also known as hang-drying.

For many applications, the dried version of the cannabis herb is required; however, like many plants, cannabis contains approximately 80% water. For this reason, drying is considered an essential step for product development (Hawes and Cohen 2015). Drying the plant not only prevents the growth of microorganisms that would otherwise rot plant tissue (based on ASTM D8196-18 which is a standard practice for determination of water activity (aw) in cannabis flower), it would also enable long term storage while maintaining potency, taste, medicinal properties, and efficacy (Hawes and Cohen 2015). This is done by maintaining the water activity level between 0.55 and 0.65 aw, minimizing the risk of mold or fungal infection while preserving the quality of the flower (ASTM D8196-18).

PLE process using organic solvent as extracting solvent coupled with supercritical antisolvent (SAS) precipitation process (1) heat exchanger for cooling, (2) pump, (3) heat exchanger for heating, (4) extractor, (5) T-mixer, (6) precipitation vessels, and (7) filter (Santos and Meireles 2015)

Vegetable oils are routinely extracted from seeds or fruits such as rapeseed, sunflower, or olive, and even brans, making them an inexpensive option. These oils are considered lipophilic due to their nonpolar characteristic, which enables selective dissolving properties. Approximately, 95 to 98% of vegetable oils consist of triglycerols whose composition is dominated by six fatty acids (Yara-Varón et al. 2017). Figure 2 shows the major fatty acids in different vegetable oils (Yara-Varón et al. 2017). Each of these has a degree of emulsifying capacity that may play a role in cannabinoid extraction. Interestingly, apart from olive oil, some specialized oils, nearly all commercial oils, are refined to eliminate the minor components. Whether this could affect cannabinoid extraction is unknown.

In this narrative review paper, the advantages and disadvantages of various drying and extraction methods have been discussed. The best methods for industries based on the final products have been reviewed and suggested. Some gaps are found in this review paper including the lack of information and knowledge about using freeze dryer for drying plant material after harvest, hydrodynamic extraction method, and a developed green extraction technique in the cannabis research area as well as cannabis industry which needs more investigations in the future studies.

This review analyses various drying and extraction processes to guide the selection of suitable methods for various types of cannabis products and applications. This is done by outlining traditional and modern methods of drying techniques, exploring the importance of solvents for extraction, visiting solventless extraction procedures, and finally comparing conventional and alternative methods of extraction.

Soxhlet extraction was first proposed by Franz Ritter Von Soxhlet, a German chemist, as a method of extraction of, primarily, lipids. However, over the years, this procedure has become widely employed for various extraction purposes, commonly used for the separation of bioactive compounds from plant matter. Soxhlet is also extensively used as a model for the comparison and development of alternative methods of separation (Azmir et al. 2013). The process begins by placing a small amount of the dried sample in a thimble that is then transferred to a distillation flask containing a particular solvent. When the overflow level is reached by the solution, a siphon is used to aspirate the solute and unload it into the distillation flask with the extracted analyte carried along into the bulk liquid. This procedure is repeated several times until total extraction is complete (Luque de Castro and Garcı́a-Ayuso 1998). For cannabis extractions using the Soxhlet apparatus, Lewis-Bakker et al. (2019) compared different types of organic solvents for the procedure and found ethanol had exhibited the highest yields of cannabinoids (Lewis-Bakker et al. 2019). As commonly witnessed by other conventional processes, the long-running time and the large amount of solvent required are limitations that not only increase the cost of operation but also cause environmental complications (Luque de Castro and Garcı́a-Ayuso 1998). These drawbacks were demonstrated by a study conducted by Wianowska et al. (2015) that compared the extraction profiles of THCA and THC using the Soxhlet extraction procedure. It was clear that the long-lasting high temperature accentuated the degradation pathway from THCA to THC and finally to CBN, resulting in high levels of THC and CBN (Wianowska et al. 2015).

Pure CBD (also called isolate) can be produced by crystallizing CBD oil/extract/distillate. CBD oil is mixed with pentane and cooled until the CBD crystallizes (crashes out). Crystallized CBD is filtered, rinsed, and dried. Purities of 99+% are possible. Re-crystallization can increase the purity even higher. All THC is removed along with minor cannabinoids.

In addition to using large volumes of solvents, chromatographic methods remove THC at a fairly slow rate and some CBD is lost in the process. At the same time, it requires an experienced operator to be available at all times during operation.

SCB-15 – Solvent Free THC Remediation System.

Pure CBD.

Broad Spectrum CBD.


CBD Crystals or “Isolate”

There are several ways to remove THC from CBD oil, CBD extracts and CBD distillate. The products can be THC Free (T Free) or low THC (0.3% or lower) which does not produce a “high”.

Another technique for removing THC from full spectrum CBD is the SBC solvent free remediation system. This THC removal process is solvent free. It uses automation to maintain the optimum vacuum, temperature, and other parameters to remove THC (and some CBD) from the CBD oil. An operator occasionally monitors the THC level by Near Infrared or HPLC. Up to 100 liters of CBD or CBG oil can be remediated in 12-24 hours.

Full spectrum CBD.

Chromatographic methods such as flash chromatography and CPC use solvents and a stationary phase to fractionate the cannabinoids from one another. In these processes, the THC is isolated and removed from the other cannabinoids. But, there is the unwanted side effect of losing some or all of the minor cannabinoids and CBD in the THC fraction.

Full spectrum is a term that applies to extracts or oils that contain all of the naturally occurring cannabinoids from the plant. For hemp products this often includes more than 0.3% THC. In order to stay legally compliant, something must remove the THC.

SCB-15 THC Remediation System.

Broad spectrum products contain all of the cannabinoids with little THC (less than 0.3%/wt). This should not to be confused with THC Free or T-Free oil which contains no THC.

The “entourage effect” is the name given to the synergistic benefits of cannabinoids and terpenes working together in your body. It has been the subject of study for many years, however we are still only beginning to understand some of the possibilities. The entourage effect can produce many different results depending on the combinations.

Consumers are attracted to the purported health benefits of CBD but understand that THC naturally occurs in hemp along with other minor cannabinoids. They do not want to consume THC because they don’t want the “high” the comes along with THC or they don’t want to possibly test positive for THC in a work drug screening. The good news is that THC can be separated from CBD so that it can be consumed without concern for unwanted THC.

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