Drying is one of the most energy intensive post-harvest processes, but necessary for the preservation of products and their bioactive compounds. The selection of the drying technique and the operation parameters may have a major influence on the chemical and biological activity of products. However, quality issues may arise due to the high temperature usage or the extended periods that the product is exposed to hot air, as reported in a range of different medical plants. In a recent study conducted by the University of West Attica, the effects of several drying methods have been tested, to see what impacts they have on the drying and quality characteristics of cannabis.
Shorter drying time, reduced energy consumption
The cannabis inflorescences were dried in a laboratory scale convective dryer at 40, 50 and 60 ◦C temperatures for a constant airflow velocity of 1 m⋅s-1. Non-stationary drying conditions were also investigated for the same temperature range under three temperature increasing rates of 1.5, 2.5 and 4 ◦C. The experiments were assessed on the drying kinetics as well as the process energy requirements and the total CBD and Δ9-THC content of the samples.
The drying data revealed that higher constant drying temperature levels and rates of temperature increase are associated with shorter drying time and reduced energy consumption. Energy consumption was found to be greater for the lower constant temperature levels (40, 50 ◦C) compared with the non-stationary conditions examined. Yet the decrease of the energy consumption of the highest temperature increasing rate and the constant 40 ◦C drying case, was 71.3%. Drying at maximum temperature level and rate of temperature increase resulted in 77.4% to 69.4% reduction in drying time respectively, compared with the lowest constant temperature drying of 40 ◦C.
A significant difference was observed in CBD concentration for the samples dried under non-stationary temperature conditions, resulting in a higher CBD level for both inflorescences (+46.7%) and leaves (+65.3%). In contrast, Δ9-THC was not found to be affected significantly at any of the examined isothermal and non-isothermal drying regimes. Additionally, the selection of the constant temperature level or the rate of temperature increase, was not found to have a significant effect on the CBD or Δ9-THC content.
Among the different cases of the drying methods examined, the study found drying at the maximum rate of temperature increase (4 ◦C⋅h-1) to be the most suitable, when taking into consideration the combination of final product quality, drying duration and energy consumption.
To read the complete study, go to www.researchgate.net