To Grind or Not To Grind

The debate is ongoing as to whether or not cannabis biomass should be ground prior to extraction. It seems there is enough evidence to demonstrate that the choice is dependent on the solvent and desired end product. This article explores the pros and cons of grinding cannabis prior to extraction along with the effects of particle size.

Cannabis can be used in many different ways. In most cases, cannabis is ground before use. For example, the "perfect" grind or particle size is integral to the "perfect" joint. Similarly, the particle size is integral to the success of an extraction. This article explores the results of grinding cannabis prior to extraction along with the effects of particle size on extraction efficiency. The debate is ongoing as to whether or not cannabis biomass should be ground prior to extraction. It seems there is enough evidence to demonstrate that the choice surrounding grinding is dependent on the solvent and desired end product.

What Is the Ideal Particle Size?

For all of the extraction solvents, the right particle size can result in an extraction that simultaneously reaches optimal efficiency while minimizing undesirable compounds. Naturally, it seems as though the smaller the particle size the higher the yield. This may be true for total yield (ntotal) by weight of extracted material, but yield specific to desired compounds is important to understanding the ideal particle size for extraction. A number of studies have demonstrated that exact theory—smaller particles size equates to higher total yield (1). Further examination of the data reveals that yield of individual compounds (ni), or selectivity, often decreases with smaller particle size (Figure 1).This indicates that further processing will be required to refine the extract to a desired end product, specific compound, or specific blend.

How Does Particle Size Affect the Yield Based on Extraction solvent?

Ethanol Extraction

As we learned in my last column(2), ethanol is an extremely efficient solvent. Ethanol extractions can be completed in as low as 15 min with a cannabinoid extraction efficiency of about 95%. Due to its efficiency, ethanol extraction can result in the extraction of undesirable compounds such as chlorophyll. By using large particle sizes for extraction, whole flower for example, the material has most of its cellular structure intact. This, along with utilizing cold ethanol, has dramatically reduced the extraction of chlorophyll. This in turn optimizes the extraction of cannabinoids and reduces the post processing steps. 

CONCLUSION: Not To Grind

Hydrocarbon Extraction

Hydrocarbon solvents also have the potential to extract at high efficiency. So, grinding cannabis biomass prior to extraction is not necessary but would increase the efficiency of the extraction. Opening the surface area for extraction using hydrocarbon solvents is also coupled with undesirable by-products such as chlorophyll and plant waxes. These components require further processing to remove them from the extract. Obviously, this results in lower overall efficiency.

CONCLUSION: Not To Grind

CO_² Extraction

CO₂ is a less efficient solvent than ethanol and hydrocarbon, therefore having room for improved yields via grinding input material. Increasing the surface area of the input material clearly leads to a more even pack of the extraction vessel achieving a more even extraction throughout the plant material and increased weight capacity within the vessel.

CONCLUSION: To Grind

What Equipment Can Be Used to Grind Cannabis? 

The cannabis industry has created ample opportunity for other industries to serve the cannabis space with established solutions. The process of grinding or milling is common practice for hops, wheat, coffee, and beyond. On a small scale, standard blenders and coffee grinders have been utilized for reducing dried cannabis particle size prior to extraction or packing joints. On a large scale, cannabis processing operations are leaning on industrial scale grain mills, leaf shredders, and scaled-up laboratory sample preparation technology.

It is important to select equipment that will offer precision and control with respect to particle size. This feature will support a more consistent extraction. In addition, ease of maintenance and sanitation is important as dried cannabis is highly resinous, which can cause resin buildup within the mill. This can translate to reduced yields if not properly managed. Frequent sanitation and maintenance of grinding equipment is integral to minimizing risk of loss or cross contamination.

Closing Thoughts

Ultimately, grinding, also known as milling, cannabis biomass increases efficiency by weight of extraction through increased input capacity, increased surface area of the plant material, increased packing uniformity, and reduced extraction time. However, dependent on the extraction solvent and desired end product, the particle size will affect the overall outcome of the end product.

References

1. M.M.R. de Melo, B. Carius, M.M.Q. Simões, I. Portugal, J. Saraiva, and C.M. Silva, The Journal of Supercritical Fluids 165, 104959 (2020) https://doi.org/10.1016/j.supflu.2020.104959.
2. L. Friesen, Cannabis Science and Technology 3(6), 14–20 (2020).

Erratum

In the July/August installment of "Extraction Science" there were several typographical errors in Figures 3 and 5.
We apologize for these mistakes.
The corrected figures appear online at: https://www.cannabissciencetech.com/view/exploring-the-chemical-makeup-of-cannabis-extract-by-method.

ABOUT THE GUEST COLUMNIST

LO FRIESEN is the founder, CEO, and Chief Extractor of Heylo. With a background in chemistry and clinical research, Lo was inspired to explore cannabis as medicine and to enter the emerging industry. She joined Eden Labs, a leading CO2 extraction equipment manufacturer to support and expand a Research and Development department. There she managed the development of their latest and greatest CO2 extraction system. In 2017, after working with Eden Labs and another cannabis processor, Lo launched Heylo with a mission to help people get more out of life with cannabis.

How to Cite this Article

L. Friesen, Cannabis Science and Technology 3(7), 13-15 (2020).