“Most current drying methods in the cannabis industry are relatively slow and inefficient processes.” Therefore, a recent research presented a drying method based on a solid-state microwave that provides fast and uniform drying and examines its efficiency for drying medical cannabis inflorescences compared with the traditional drying method. “This method resulted in a considerable reduction of drying time, from several days to a few hours.”
Traditional methods
Usually, traditional drying takes place under aeration in closed rooms with controlled temperature and humidity levels for at least 5–6 days and up to 2 weeks. Either the whole plant or the branches with inflorescences are hung upside down. The researchers explain that as the bud dries, water from the stem slowly migrates into the bud, slowing the drying process. “Another variation is ‘screen drying,’ in which trimmed buds are placed on drying screens. In this method, the drying time is shorter due to the large effective surface area available for drying. However, it results in uneven drying as the size of the buds influences the drying rate.”
The alternative
The study examined a solid-state microwave heating technology as a possible method to dry cannabis inflorescences rapidly and efficiently without deteriorating the quality of the resulting product. The drying apparatus was a prototype based on a Miele oven used for cooking that has been modified to eliminate the heating function. The apparatus combines an infrared sensor for cannabis temperature measurement and an RF module with a feedback control loop. The RF module is controlled by an external computer with software displaying the parameters relating to the drying process, including the forward power, reflected power, frequency, phase, energy absorption, and temperature. Dedicated shelves were designed and built for the oven to enable cannabis drying in this prototype. A fan was included in the system to circulate the air and remove the moisture.
Hours instead of days
The researchers found solid-state microwave drying achieved similar moisture evaporation from cannabis inflorescences in only a few hours, rather than several days with traditional drying. “The solid-state technology allows for frequency control, which is practically impossible in magnetron technology used in conventional microwave ovens, and power control, which is more subtle than allowed by commonly used magnetrons. Moreover, solid-state power amplifiers have the ability to provide feedback on the dynamic state of the processed material. This technology, therefore, produces a more uniform and consistent energy field during the heating process, resulting in an improved product in shorter times. Radio frequencies excite and heat products internally, and not just the outer layers. The bulk heating effect produces uniform heating throughout the material, avoiding the large temperature gradient that occurs in conventional heating systems.”
As this method relies on heating and high temperatures were shown to affect the composition of cannabinoids in the plant, the researchers evaluated the cannabinoid derivatives at different drying temperatures. “At a drying temperature of 80°C, the concentration of Δ9-THC was high, probably due to the high temperature that promotes the heat-induced decarboxylation of Δ9-THCA into Δ9-THC. Of the different temperatures tested, the MW drying temperature that shortens the drying time substantially while retaining the phytocannabinoid composition of the cannabis inflorescences was in the range of 50–60°C. For terpenoids, which are more volatile, at 40°C and 50°C, their concentrations were relatively similar to that of traditional drying. Thus, the optimal drying temperature that significantly shortens the time while retaining the composition of the secondary metabolites was found to be 50°C.”
To read the complete study, go to www.liebertpub.com