Industrial drying of cannabis (Cannabis sativa) using tray and hang air-drying systems

Timely harvest and drying are critical postharvest parameters for cannabis production. Cannabis sativa grown outdoors in Mirabel, Quebec, Canada, was subjected to two harvests, one week apart, to determine influence of initial moisture content on drying behavior and phytochemical stability. Two conventional air-dry methods, tray-drying and hang-drying, were evaluated in an industrial-sized facility under controlled conditions (15–25 o C temperature and 40–60% relative humidity). Real-time relative humidity monitoring tracked drying progression and identified end of the drying process. Irrespective of harvest or drying method, cannabis biomass exhibited a characteristic drying curve, with an exponential decline in moisture content, achieving ≤12% moisture content at 6 days. Higher initial moisture content in the second harvest, attributed to pre-harvest rainfall, significantly increased early-stage drying rates. Tray-drying exhibited a higher drying rate than hang-drying. Moisture diffusivity coefficients were low (4.1 × 10⁻¹⁰ m² s⁻¹) for all drying conditions. Colorimetric analyses suggest that both tray and hang air-dried biomass display greater pigment degradation when compared to the same harvested biomass freeze-dried in a laboratory (used as a preservation reference). Harvest time significantly affected cannabinoid concentrations; cannabis inflorescence harvested one week later exhibited greater bioaccumulation of cannabigerolic acid, tetrahydrocannabinol, tetrahydrocannabinolic acid, total cannabigerol, and total tetrahydrocannabinol by 60.2%, 40.7%, 26.1%, 57.6%, and 26.3%, respectively. Tray and hang air-drying promoted partial decarboxylation, resulting in increased tetrahydrocannabinol and cannabigerol concentrations while maintaining high levels of their acidic precursors. Findings highlight key drying factors that are essential for ensuring consistent cannabis product quality for outdoor operations.