5 Critical Extraction Yield Considerations in CO2 Extraction

essential oil extraction machine

Biomass Potency

Selecting high-quality cannabis biomass is a crucial first step in creating high-quality cannabis distillate. As the cannabis industry expands with new-to-industry professionals, we find it important to start by defining the term “biomass”.

What is Cannabis Biomass?

industrial co2 extraction machine
industrial co2 extraction machine

It’s a common misconception that cannabis distillates are produced from the same flower that is packaged and sold to be smoked. During the cultivation process, the main flower cluster (or “bud”) is usually removed and packaged for sale. The remaining leaves, stalks, and stems are considered cannabis biomass. Though biomass usually has a lower potency of desirable compounds (like terpenes and cannabinoids) than buds, there’s still plenty remaining for a skilled extractor to extract a high-quality cannabis distillate.

Biomass potency varies widely across different farms and cultivars. Given this fact, and that this piece of information will determine your overall yields more than any other factor – potency is by far the most important piece to consider.

When purchasing biomass, assessing the biomass on a dollar/mg or gram of cannabinoid basis is perhaps the most accurate form of assessing the cost of your inputs.

A final consideration that is often overlooked, is that 1-2% of the cannabinoids will always remain in the biomass after extraction, with the exception of perhaps powder milled material – which our next point will cover while this fine of a mill is not recommended.

This means that generally if one batch of biomass has a potency of 10%, you can easily get 80-90% yields (% of cannabinoids extracted compared to total cannabinoids in biomass). However, if another batch of biomass has a potency of only 4%, you will probably never attain yields higher than 75%.

Why is Biomass Selection So Important?

It’s important to select biomass with the right amounts of the desired cannabinoids (like THC and CBD) and terpenes to support the creation of your desired finished products. Testing for cannabinoids, terpenes, pesticides, and heavy metal contents before committing to a partnership with a grower or cultivator is critical to ensure you’re entering into a relationship that will get you the highest quality inputs for your process.

How to Source the Best Cannabis Biomass

Here are a few steps you can take to ensure you’re sourcing the best biomass for your cannabis distillate products:

  • Perform a visual inspection – it’s fairly easy to visually identify what your biomass is comprised of; buds have the highest potency of cannabinoids, whereas leaves contain a lower potency, and stalks and stems contain very few desired compounds
  • Ensure your biomass is “homogenized” – since your biomass can come from a variety of strains and sources, it’s important to ensure the distinct plant products have been properly mixed together so they can be tested as a single entity
  • Test the potency of compounds in the biomass – test the biomass for its potency of cannabinoids, terpenes, pesticides, and heavy metals in relation to the concentrations tolerated by your local AHJ
  • Visit your cultivators – review the grow sites, meet the people, see how they deal with pests, assess the quality of their water, etc. (learn more here)
  • Perform a micro-extraction – perform a low-tech, small-scale extraction on a sample of biomass and test the quality of that distillate.

The benefit of milling biomass before CO2 extraction

Regardless of the extraction process being employed, post-harvest drying and curing methods are essential steps for downstream product development. Similarly, specific strains of cannabis have unique characteristics that affect extraction efficiency.

The finer you mill your biomass, the more surface area is available. The more surface area available, the quicker the CO2 fluid will dissolve the extracts(essential oil or cannabinoids).

However, an important consideration is that there are also compounds within the biomass that we do not want to extract if we can help it. A lot of these compounds are found within the cells of the plants, and it would cause a lot of unnecessary refining to obtain cannabinoids if we were to mill the biomass so fine (powder milled for example) that we break the cell wall and subject our solvent to these undesirables as well. 

In addition to more ineffective substances (waxes, chlorophyll), which are more easily grounded, biomass that is too finely ground can also cause problems for extraction, such as CO2 fluids that cannot pass through them and thus cannot dissolve those extracts. For example, in the extraction of Ganoderma lucidum robe powder, it is one of the substances that does not require grinding, but its particle size is so small that it must be made into slightly larger particles for good extraction.

The optimal milling parameters

• 10% moisture content of pre-milled cannabis biomass
• 3000-3500 micron mill size
• 300-400 mill blade speed

Temperature

The extraction temperature is another very important parameter that affects the density of supercritical CO2. Compared with the extraction pressure, the effect of extraction temperature on the supercritical CO2 fluid extraction process is much more complicated.

Under a certain extraction pressure, there are two trends in the effect of extraction temperature on the extraction of vegetable oils:

  • As the temperature increases, the oil yield gradually increases, and when it exceeds a certain temperature, it gradually decreases. This situation occurs when the extraction pressure is high.
    This is because when the extraction pressure is high, the CO2 density is high, the compressibility is small, and the CO2 density decreases less when the temperature is raised, but the vapor pressure of the components to be separated and the diffusion coefficient of the material is greatly increased, and the dissolution capacity is improved.
  • As the temperature increases, the product yield shows a decreasing trend, which occurs at lower extraction pressures. This is because near the critical point of supercritical CO2, when the pressure is low, the compressibility of supercritical CO2 is large, and the density of CO2 drops sharply when the temperature is raised. At this time, although the volatility and diffusion coefficient of the separated components can be increased, it is difficult to compensate for the decrease in solubility caused by the decrease in CO2 density.

How to choose the extraction temperature

In addition, as the temperature increases, while the extraction rate increases, the solubility of impurities will also increase accordingly, thereby increasing the difficulty of the separation and purification process, which may reduce the yield of the product, and high temperature may cause certain components The denaturation, decomposition or failure of the extract, so these factors should be considered comprehensively when selecting the extraction temperature.

Recommended supercritical CO2 extraction temperature for vegetable oils
Since most vegetable fats and oils contain unsaturated fatty acids, the extraction temperature should be relatively mild, generally between 30 and 50 ℃.

Pressure

From the initial chosen extraction pressure, increasing pressure increases wax/resin concentration in the extract.
Pressure over 5000 psi at 45 deg C causes chlorophyll extraction, increasing pressure increases chlorophyll in the extract.

Flow rate

Maintaining flow rate at higher pressures is more difficult due to a loss of CO2 supply (especially when using tanks and the cylinders are emptying). Increasing flow rate can cause dry ice accumulation, resulting in a higher chance of icing up lines unless additional heat is applied. Decreasing flow allows for the material to be in contact with the solvent for longer, increasing potential yield. Decreasing flow slows processing.

Works Cited

  • “What is Cannabis Biomass? How to Source the Best One for Cannabis Extraction”, extractX Ltd, Visited 17 Aug, https://www.extractx.com/blog/how-to-source-the-best-biomass-for-cannabis-extraction/