What is the Best Extraction Method for Hemp?

There are several ways to extract CBD oils from hemp. The most popular methods use supercritical CO2 or ethanol to dissolve cannabinoids that are in the resinous plant trichomes, leaving the undissolved plant material to be discarded as waste. Although both extraction methods have been widely deployed, supercritical CO2 extracts are considered by the public to be cleaner and safer than ethanol derived oils for the following reasons:

1.   Purity: Ethanol extracts carry with them known and unknown risks related to prolonged and repeated exposure to unnatural denaturant chemicals[1],[2] that are added to pure ethanol to make the extraction method affordable. Although these chemicals are often removed to “safe” levels, they are not fully removed from extracts. The remaining solvent contaminants are called chemical residuals by the FDA and must be controlled and tested because the residuals have “no therapeutic benefit” and in some cases are toxic or carcinogenic at high levels.[3]

2.   Testing using invalid test methods: A partial list of common denaturants include: acetone, isopropyl alcohol, hexane, hexanes, heptane, butanol, methyl tertiary butyl ether.[4] Testing for “safety” is required but residuals are not always measured in hemp extracts with validated test methods[5] considering the specific denaturant mixture used in extraction. Rather, a generic solvent method is typically employed. This means the risk of missing a major potential contaminant is highly increased.

3.   Unknown risk of negative health consequences: Health dangers of such additives are well documented[6] but only partially understood in the context of cross factors including age, health, drug interactions, effects on the brain and cognitive & emotional function, and susceptibility to negative health consequences. Despite all the years of research, more research investigating the long-term solvent exposure in humans is needed to accurately assess risk. Due to these reasons, the healthy, natural CBD you expect from hemp may not be so healthy.

4.   We encourage consumers to look for a label that says “Made with CO2”. CO2 derived hemp and CBD oils are widely regarded as the highest quality, chemical residue free oils produced. CO2 extraction has advantages over ethanol as the extraction media on many different levels. Drastically lower operating costs are a key benefit of CO2 extraction. Over time, lower operating costs accumulate and continue to build value throughout the life of the equipment.

HOW TO PRODUCE CANNABIS OILS: Plant Workflow

Step 1: Biomass Preparation

Bucking

Hemp or cannabis biomass preparation starts with removing the flower from the stems. This process is often referred to as bucking and can be accomplished with a bucking machine or by hand.

Bucking machines eliminate the labor-intensive part of obtaining the flower. One alternative to bucking is to chop the entire plant (stock, stem, seed, and flower) in a commercial combine. However, including the entire plant reduces efficiency by as much as a third, and may produce low quality isolate and distillate.

Hemp or cannabis biomass is much easier to buck when it includes less than 10% moisture. To dry cannabis biomass, we recommend hanging the whole plant inverted for 24-48 hours in a humidity and temperature-controlled room.

A hemp dryer on the other hand will dry large volumes of hemp. Drying equipment employed in this case can include fluidized beds, rotary kiln dryers, or belt driven infrared dryers. As an alternative to machinery, many hemp farmers let their crops dry in the field. This works well as long as the harvest time is cool and dry.

Grinding

Once the hemp or cannabis has been bucked and dried, it is granulated. In general, smaller particles (200-1000 microns) are desirable and tighter particle diameter distributions are better for extraction throughput. Also, sticks, stems, and seeds that made it through the bucking process should be removed before grinding. Several kinds of mills are available on the market to accomplish these goals including hammer mills, shear mills, and cone mills.

Depending on the desired processing volume, a typical grinding operation will include a hammer or a cone mill. The mill is assisted with vacuum cyclone collection.

Decarboxylation

Once the materials are milled, they can be extracted or further processed to convert the acidic forms of CBD or THC into neutral molecules. This further processing is known as decarboxylation[7] and the resulting biomass is referred to as decarb material.

Conversion of the acidic to the neutral form is desirable from the standpoint of throughput and for formulation reasons. However, acid forms are also desirable for specific types of formulations. Decarboxylating is required for a quality distilled product.

Decarboxylating before extraction has the advantage of speeding up the extraction process and allowing the gentle collection of pure, full-spectrum terpenes. Because decarboxylation involves the use of heat and vacuum pressure, the evaporation point of the terpenes is low enough to be removed from the biomass without damaging the terpenes themselves. Once removed, the cold trap chilled condenser will collect full spectrum terpenes that would otherwise be unobtainable further down the processing line.

Full Spectrum terpenes are completely natural and easy to dilute into formulations. Processing of terpenes earlier, rather than later, is a huge advantage for formulations and aroma engineering.

Step 2. Extraction

How to extract hemp oil: Supercritical CO2 extraction has become the preferred method for extracting THC and pure CBD oils. This extraction method serves consumer markets with the most demanding standards for safety, quality, purity and consistency. Progressive brands are boldly stating “extracted with supercritical CO2” on package labels. This is due to the fact that CO2 oil is purer than ethanol derived oil.

Supercritical CO2 extractors use carbon dioxide (CO2) at elevated temperatures (40-60oC) and pressures (3000-5000 psi, 206-345 bar) to extract soluble compounds from natural products, leaving behind no chemical residues after extraction. Above 31oC (critical temperature) and 1071 psi, carbon dioxide becomes a supercritical extraction solvent, which has an increased capacity for solubilizing non-polar compounds like cannabinoids. Extraction machines raise the temperature and pressure of the liquid CO2, providing highly efficient oil extractions in a short period of time.

The CBD extraction process begins by filling the extractor machine with hemp or cannabis. Once the operator and lot of material are scanned in, then the latest calibration and maintenance are checked before operation. Once the extraction method is running, CBD extract or THC extract is produced and collected hourly.

Step 3. Dewaxing, Distillation, and Isolation

Dewaxing

How to make winterized oil: Winterization is typically needed to remove extracted heavy waxes; the resulting oil is referred to as dewaxed oil or winterize oil.

Winterizing is usually accomplished by dissolving the extract in a small amount of food grade ethanol, cooling the ethanolic extract to -20oC, and then filtering. At -20oC, the precipitation of wax in ethanol can take up to 24 hours to complete. However, many operators process materials prepared the day before in a first-in-first-out manner.

Sub-critical CO2 extraction methods can also be used to remove the need for winterization and is popular for producing terpene rich oils.

Filtration with large filter funnels offers a high throughput means of separating the precipitated wax from the ethanolic oil.

Ethanol is then removed and recycled with a thin film evaporator or a rotovap. Two advantages of a thin film evaporator are: it is continuous and has a high throughput.

Solvent Removal

How to remove solvents from ethanolic extracts: Solvent recovery is necessary to recover or remove solvent from CBD oil after ethanol extraction or winterization. The first step in removing ethanol from an extract is to heat the ethanol to its boiling point where it is evaporated. The ethanol vapor is then transported to a different location where it is condensed back into a liquid. This process is called fractional distillation. To accomplish fractional distillation quickly and with high throughput, solvent recovery systems must be designed that can keep up with the solvent removal demand.

The small amount of ethanol used in the winterization process does not carry the same drawbacks as long as UL, CE, and pure ethanol is used. Additionally, less ethanol is required for winterization compared to extraction. In most cases, occupancy and storage requirements can be managed as a factory industrial (F-2 occupancy).

Solvent sourced contamination is not an issue because a higher grade of ethanol is used and the primary concentration step has already been completed. The use of in-process hoods keeps production areas ventilated below the lower explosive limit (LEL). .

Distillation

How to make distillate: Distillation can be accomplished with short path distillation equipment or wiped film evaporation equipment. A distillation machine is typically used to improve the potency and color of the extract. Potency is typically improved 10-30% while the color of the oil is converted from an opaque dark amber – to a light amber – then to a clear light yellow.

Chromatography

Chromatography is a separations method necessary for the remediation and isolation of various compounds into their individual components. This is essential for remediating THC from CBD products, identifying and removing unwanted materials, and isolating cannabinoids for specific downstream product formulations.

In the hemp and cannabis extraction industry, chromatography allows manufacturers to distinguish a list of compounds in the cannabis plant and create a specifically formulated product that's both legal and tailored to the marketplace demands. Chromatography is also effective at identifying and removing unwanted pesticides, and other residual chemicals. These are essential factors in creating a healthy, safe, desirable product for the end user making supercritical chromatography an essential part of your production.

CBD Crystals or THC Crystals

How to make isolate: CBD crystals are made by precipitation in a non-polar solvent, which involves dissolving distillate into the solvent, cooling the solvent down to induce precipitation of CBD, washing the crystals, and then removal of the non-polar solvent. When using jacketed stirred reactors, crystallization and precipitation processes can be used to produce several hundreds of kg of crystal CBD isolate.

Just like in the winterization process, the amount of solvent used is less than when compared to the solvent required for extraction. Crystal production rooms can be designated as separate control areas, making the amount of solvent in the room and building more manageable.

THC crystals are made by similar precipitation. Typically, an ethanolic extract is subjected to very low temperatures thus causing precipitation of the crystals. Just like CBD crystals, they’re washed and then the solvent is removed.

There are many different methods to extract and process hemp and cannabis. When extracting at a large scale with many different end products being the objective, CO2 is the gold standard for product development and consumer safety.

If you ever have any questions about extraction, building a hemp successful hemp business, or taking your hemp knowledge even further, you can always reach out and I will do my best to get you what you're looking for.

References

[1] eCFR — Code of Federal Regulations- TTB Alcohol and Rules for Specially Denatured Alcohol https://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&sid=fc3be5d2e97afdd4aed5fb7b5c26309c&rgn=div5&view=text&node=27:1.0.1.1.17&idno=27#se27.1.21_1112 (accessed Dec 8, 2019).

[2] Medicines Agency, E. ICH Guideline Q3C (R6) on Impurities: Guideline for Residual Solvents Step 5.

[3] USP 467 Residual Solvents; 2007.

[4] eCFR — Code of Federal Regulations- TTB Alcohol and Rules for Specially Denatured Alcohol https://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&sid=fc3be5d2e97afdd4aed5fb7b5c26309c&rgn=div5&view=text&node=27:1.0.1.1.17&idno=27#se27.1.21_1112 (accessed Dec 8, 2019).

[5] McArdle, J. V. Residual Solvents. In Specification of Drug Substances and Products: Development and Validation of Analytical Methods; Elsevier Ltd., 2013; pp 143–154. https://doi.org/10.1016/B978-0-08-098350-9.00007-2.

[6] (PDF) Overview of impurities in pharmaceuticals: Toxicological aspects https://www.researchgate.net/publication/259150621_Overview_of_impurities_in_pharmaceuticals_Toxicological_aspects (accessed Jan 6, 2020)

[7] Veress, T.; Szanto, J. I.; Leisztner, L. Determination of Cannabinoid Acids by High-Performance Liquid Chromatography of Their Neutral Derivatives Formed by Thermal Decarboxylation. I. Study of the Decarboxylation Process in Open Reactors. J. Chromatogr. A 1990, 520 (C), 339–347. https://doi.org/10.1016/0021-9673(90)85118-F.