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How to grind the biomass for (essential oil) extraction?

How to grind the biomass for extraction of the essential oil
When grinding biomass for an extractor/CO2 essential oil extraction equipment, size matters a lot. Grinding the plant material too small can create low-quality oil, and even reduces the extraction efficiency in the CO2 extraction process; grinding too large can leave valuable target extract in the waste material. 
Whether extracting with supercritical CO2, hydrocarbons, or ethanol, finding the right particle size for solvent and extractor will increase returns and may even speed up the production.

Extraction Yield and Grinding Biomass

How finely mill or shred will be extraction biomass plays a large role in determining how much biomass can fit into the extraction chamber. The finer you mill your biomass, effectively lowers the selectivity of the solvent while increasing its power, the more surface area is available, and the quicker the solvent will dissolve the target extract. Depending on the solvent type, this can be a good thing. A smaller grind size speeds up the action of CO2. But for a powerful solvent like ethanol, grinding too fine can be a mistake.

But you have to know that there are always two sides to things, if you grind very fine, you’re increasing the surface area and making the cannabinoids and terpenes easier for the solvent to access, there will be unwanted results, such as extra ineffective chlorophyll and wax in the hemp extraction process, those elements make the oil less desirable and increase the post-processing necessary for most final products.; in the CO2 extraction process, too fine The particle size of the raw materials will become viscous, and it will be difficult for the supercritical CO2 fluid to pass through them, thus affecting the efficiency of the extraction.

Grinding and Extraction of Cannabis

The finer you mill your biomass, the more surface area is available and the quicker the solvent will dissolve the cannabinoids, which include:

  1. Terpenes — are the compounds that give cannabis and hemp products their distinctive aromas and contribute to their varied flavors. Different combinations of terpenes are widely considered to be a driving factor in the type of high that consumers experience.
  2. Crude oil — the dark, a highly viscous substance similar in texture to thick molasses. Although it is rich in the major (CBD and THC) and minor cannabinoids (CBN and CBG), it still contains undesirable components such as plant particulates, solids, and waxes. Removing these components requires that crude oil be further refined. Crude oil is one of the major building blocks of the cannabis industry because most end-products start off as crude before being further refined and purified.
  3. Resin — the valuable oily compounds contained in trichomes, including terpenes, flavonoids, and high concentrations of cannabinoids such as THC. Resin can also contain undesirable elements like waxes and chlorophyll. Resin is typically further processed into dabbling concentrates.

How fine should grind biomass be for a co2 extraction machine?

For CO2 extractors, we recommend grinding the biomass to a particle size of 40-80 mesh.

In general, CO2 could use a little extra kick for dissolving target extract (such as cannabinoids and terpenes). Grinding to a smaller size helps it pull out the good stuff at lower pressures (without the terpene-compromising high temperatures). And it helps in other ways too.

Because CO2 extractors run at super-high pressures (like 2,000 psi), the movement of the solvent through the material column can create “channeling.” When the particle size is too large or the grind is inconsistent, the solvent channels rivers in the material where it can flow through more easily. This leaves other areas of the plant material untouched and under-extracted.

The solution is smaller particle size and a consistent grind. When all the plant material is evenly packed and homogeneously sized, the supercritical CO2 reaches all areas of the extraction column and retrieves all the oil possible.

So why the range of particle sizes for CO2? After all, there’s a big difference between 40-80 mesh.

Production objectives vary from producer to producer, and so does the plant material. Some strains may require a smaller particle size and longer runs. Other high-potency strains may do better with a larger size and shorter runs because they extract more easily. The desired oil purity may play a role too. Shorter runs with a larger particle size yield a better oil — but less of it.

How fine should grind biomass be for an ethanol extractor?

Biomass (such as cannabis and hemp) should be milled to a particle size of 5/64” – 1/4” for ethanol extractors.

Ethanol is a very powerful solvent. Extraction is quick and best performed at lower temperatures so that less chlorophyll and wax co-extract from the material. A coarse grind is best, and some producers choose not to mill the material whatsoever. For most strains, the optimal grind size for ethanol is on the high end of the 5/64” – 5/16” range.

Another benefit of grinding for ethanol extraction is an increase in production capacity. Grinding also decreases the solvent necessary per pound. When plant material is ground, more material can fit in the extraction vessel per run, thus increasing production speed and reducing the ethanol that needs to be distilled in post-processing.

How fine should grind biomass be for a hydrocarbon extractor?

Biomass (such as cannabis and hemp) should be milled to a particle size of 5/64” – 1/8” for hydrocarbon extractors.

Though the perfect grind for a hydrocarbon extractor can be a little larger or smaller depending on the strain, 5/64” – 1/8” is the sweet spot. Hydrocarbons like butane and propane are powerful solvents. Yet, because the solvent flows through the material under pressure, channeling can occur like it does with a CO2 extractor. The channeling problem is less severe, but it’s still best to avoid large particle sizes and unmilled material.

Milling Biomass Considerations

10% moisture content of pre-milled biomass, this is very important.

Milling can produce desirable (potency, extraction efficiency) and undesirable outcomes.

It is also important to note the positive correlation between uniformity of particle size distribution and the milling blade speed. An optimum blade speed of 300-400 rpm is suggested to maximize the particle size distribution while also protecting the integrity of cannabis volatiles.

Furthermore, optimizing the downstream filtration process following extraction is negatively impacted, from an operational perspective, when cannabis biomass is milled ultra fine (less than 1/16” or 2000 microns for ethanol extraction or less than 80 mush for CO2 extraction). The particulate build-up and subsequent clogging of filtration media with finely milled biomass require more frequent cleaning and replacement of the filtration systems.

Mill size

One other impact of mill size is on the productivity of your extraction process. More fine-milled biomass can be uniformly packed into the filter bags used in ethanol centrifuge extraction processes or loaded directly into CO2 extraction vessels compared to coarse-milled biomass. So mill size directly influences how many pounds of biomass can be processed during each extraction.

Heat from grinding

The heat generated by grinding is another issue that needs to be paid attention to in the extraction of essential oils. For example, when we need to grind large chunks of plant rhizomes, if we do not use a special slicer to cut them into small pieces and then grind them, they will a lot of heat is generated in the machine and some essential oils and terpenes are lost.

When the machine grinds plant material, it also generates high heat due to high-speed operation, so there is usually a water cooling device in the grinding machine.

Works Cited

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