Post-harvest cannabis research is extremely limited. There is little to no peer-reviewed scientific evidence confirming the best temperatures, humidity levels, and methods of storing your weed. While you have certainly heard a lot from cannabis enthusiasts and storage companies about best practices, the truth is that those recommendations are anecdotal and have yet to be substantiated by a robust body of empirical evidence.
These Factors Will Degrade Your Cannabinoids
Here is what we know about cannabinoid degradation based on limited existing evidence.
In 1976, the Journal of Pharmacy and Pharmacology published a landmark study on cannabis storage by Dr. J.W. Fairbairn, Dr. J.A. Liebmann, and Dr. M.G. Rowan of the University of London’s School of Pharmacy. Fairbairn et al. stored nine samples of cannabis concentrates in different conditions for up to 2 years. The researchers determined that exposure to light resulted in the greatest losses of cannabinoids.
A 2019 Forensic Science International study by Italy-based researchers Luca Zamengo, Chiara Bettin, Denis Badocco, Valerio Di Marco, and Giampietro Frison confirmed these findings. Zamengo et al. found that light increased the speed and stoichiometry of the conversion of THC to cannabinol (CBN), a non-psychoactive cannabinoid that can only be produced in the plant through oxidation.
For example, THCA is a non-psychoactive cannabinoid that may have some medical use. When cannabis is heated, THCA converts to THC, and THC definitely has medicinal effects. Most notably, it can get you high. However, if cannabis is exposed to too high a heat for too long, THC will degrade. Terpenes are also affected by heat. Terpenes are activated by heat but can be destroyed if that temperature reaches or exceeds their individual boiling points.
Fairbairn et al. determined that cannabinoids were best preserved for 1 to 2 years when stored at room temperature. Zamengo et al. found that temperatures cooler than room temperature slowed the conversion of THC to CBN, but they did not prevent it.
In her Cannabis Cultivation Virtual Conference presentation called “Exploration and Optimization of Drying and Curing,” Dr. Allison Justice, Vice President of Cultivation at Outco (a San Diego-based cannabis production and processing company) reports that the primary goal of cannabis drying is to prevent immediate spoilage caused by microbial growth and germination, extend shelf life, and dry slowly enough so as not to compromise terpenes.
She states that the ideal conditions for this seem to be a drying room with a temperature of 60 to 70 degrees F and 40-60% humidity. However, she notes that we don’t know exactly how much water activity in cannabis will promote microbial growth.
Fairbairn et al. found that air was another significant factor in the degradation of cannabinoids due to oxidation. The researchers found that even when stored in dark locations, cannabis that is exposed to air will result in the synthesis of THC to CBN. Elevated levels of CBN are indicative of decreased THC levels because CBN is the byproduct of oxidized THC.
While this suggests that the cannabis will be less psycho-actively potent, it is also an indication that consumers of such THC-degraded cannabis may experience the potential medicinal effects of CBN including bronchodilation, sedation, anti-inflammation, and anti-convulsion.
Storage Options We Recommend
- Store your weed in a dark place. Researchers have cited light as the primary agent of cannabinoid degradation. Use an opaque glass or metal container to shield your cannabis from light. Avoid plastic and wood. Chemicals from plastic can leach into your weed and alter its taste or have other long-term effects on your health. Direct contact with wood can alter the taste and fragrance of cannabis.
- Keep the temperature cool. A 2004 Journal of Toxicology study by Germany-based researchers Gisela Skopp and Lucia Pötsch suggested that the ideal temperature for storage is 39 degrees F. Cannabis stored in environments above room temperature will see a more rapid conversion of THC to CBN.
- Avoid air exposure. A 1999 United Nations Office on Drugs and Crime study by University of Mississippi researchers Stephen A. Ross and Mahmoud A. Elsohly found that prolonged exposure to air causes THC to convert to CBN. Storing cannabis in an airtight container will slow this process.
- Keep your weed dry. Moisture promotes microbial growth, and that can lead to moldy, mildew-infested, or otherwise diseased weed. As Justice mentions in her presentation, there is no clear empirical evidence indicating what moisture levels are optimal for cannabis storage. However, she notes that between 40-60% RH seem to be effective at inhibiting microbial growth.
I’m a Regular Cannabis Consumer. Do I Need to Worry About Storage?
Current evidence is most relevant to long-term storage. If you tend to replenish your stash every week, you’ll probably smoke your weed before THC degrades. Skopp et al. determined that THC stored at room temperature will begin to degrade in about 2 weeks. As long as you aren’t storing your cannabis in direct sunlight, dousing it with water, and leaving it in the open air, you likely won’t notice any cannabinoid degradation.