The number of ways that growers treat, cure, and store their flower post-harvest has increased dramatically in the last decade. While the humble home grower might stick to simpler, low-tech solutions, many commercial cultivators have poured millions into methods to help them achieve consistency and quality at scale. Some of these technologies have proven more effective than others, while some still struggle to fully explore the comprehensive, long-term effects they have on cannabis.
New research to better understand cannabis and its preservation is undertaken around the world every day, though many of the results of that research fail to filter down all the way to growers themselves. Here at Grove Bags, we’re always searching for new data to better inform our development of materials that fit the needs of the plant and those that grow it. In that pursuit, we’ve come across a few interesting findings that may help inform your next move.
Freeze-Drying Doesn’t Benefit Your Terps
In the May 2024 edition of Analytical and Bioanalytical Chemistry, Italian researchers looked at the influence of drying and storage conditions on cannabis – specifically at their impact on cannabinoids and volatile compounds (or the volatilome, including terpenes).
As a part of their conclusions, they found that freeze-drying flower resulted in preservation of cannabinoids, but a loss of other compounds:
It has been demonstrated that tray drying (TD) is the best method to reduce water content in inflorescences while maintaining a rich VOC profile. Conversely, the freeze drying method, being useful to preserve cannabinoid content, pre-venting decarboxylation of acid cannabinoids, leads to a loss of volatile compounds responsible for the characteristic aroma of cannabis.
While freeze-drying might seem an attractive option to growers who want to get their flower to market faster, sacrificing your strain’s unique aromas is a trade-off that most aren’t willing to make, especially if they care about the quality and integrity of their harvest.
How You Trim Matters
Dry trimming, in our experience, is preferred by most growers over wet trimming, especially for top-shelf quality. While many have their own anecdotal evidence that justifies their choice, it turns out that your trimming method can have an impact on both your cannabinoid and terpene content.
In the July 2024 edition of Medical Cannabis & Cannabinoids, one study illustrated how different trimming techniques can affect the finished flower:
Our results show that a gentle pre-drying trim increases total cannabinoid content more effectively than other methods. By partially retaining sugar leaves, this approach possibly supports an enhanced flow of precursors necessary for cannabinoid synthesis and provides stress signals that elevate cannabinoid production. Conversely, for most mono- and sesqui-terpenes, only post-dry trimming significantly raised their levels. The variation in cannabinoid and terpene content across different trimming methods may be due to differing stress responses from mechanical injury before drying, influencing the plant’s defensive system and thus affecting cannabinoid or terpene synthesis.
Interestingly, this research indicates that wet trimming has a more substantial positive effect on cannabinoid content, while dry trimming is more beneficial for terpene levels. Whether this will play a role in how growers decide to process their flower in the future has yet to be seen, but it does raise questions about how different cultivators determine what ‘best quality’ or ‘top shelf’ really means to them.
Long-Term Cannabis Stability May Warrant Re-Testing of Products
A conference paper from academics in North Macedonia looked at the long-term storage and stability of cannabis oil and how it might impact the effectiveness and regulation of medicinal products.
These researchers found that:
The results of the CBD cannabis crude oil stability study showed a decreasing effect in less than 13% of the CBD content, from 72.8% to 64.7%, 73.6% to 71.2% and from 80.8 to 75.4%, after 12 months of storage. On the other hand, HPLC analysis of THC cannabis crude oil showed an increasing effect on THC content in less than 10%. The THC content in the oil increased from 70.8% to 71.5%, 72.6% to 80.4% and from 71.2% to 77.7%
Notably, they found that after 12 months of storage, CBD levels decreased while THC levels increased. While CBD and THC are just two of a myriad of cannabinoids found in the plant and its extracted oil, these findings do support the researchers’ recommendation that “potency retesting is requested after a prolonged period of time, and care should be taken when comparing sample concentrations”.
Controlled Gas Exchange May Hold the Keys to Curing
Much of our own research has supported the idea that an effective curing environment – one that most effectively retains the full spectrum of volatile compounds found in cannabis – is best created by utilizing materials with a specific gas exchange rate for the storage vessel. ‘Gas exchange rate’ refers to the speed at which gases, like oxygen and CO2, move across a membrane. As indicated by our 12-week stability study, our TerpLoc® material allows oxygen to escape the pouch while holding on to CO2. This CO2-rich environment may also play a role in elevating the water use efficiency of the flower, allowing it to continue using residual moisture in phytochemical processes that generate terpenes.
Knowing that this gas exchange rate, and the resulting environment within the bag, can play such a significant role in retaining volatile compounds like terpenes also gives us a better picture of why the ‘old school’ jar-burping method of curing works, but can be majorly improved upon. When curing in jars or other vessels that require burping, the entire environment inside is ‘reset’ as all of the gases, including valuable CO2, are evacuated and replaced with ambient air. As those headspace gases escape, so do gaseous terpenes within the container. Using an auto-curing vessel that requires no burping, like a Grove Bag, terpenes that would otherwise be lost forever are instead kept suspended within the increasingly CO2-rich environment until reattaching to the flower. We will be continuing along this research path and sharing results along the way as we analyze ongoing experiments.
The scope and scale of cannabis research has come a long way since the legalization movement began, and it only seems to be accelerating. In the arenas of drying, curing, and storage, there is still much to explore, but one thing has only become more apparent: a grower’s choice of post-harvest processes at each stage can have a dramatic impact on their quality, potency, and consistency.
