Postharvest Drying and Curing Affect Cannabinoid Contents and Microbial Levels in Industrial Hemp (Cannabis sativa L.)

Postharvest operations affect the yield and quality of industrial hemp (Cannabis sativa L.). This study aimed to investigate the postharvest drying and curing effects on the key quality and safety indicators of cannabinoid-type hemp. Freshly harvested hemp inflorescence of Hempress and Wild Bourbon cultivars were dried by three methods: (1) Hot air drying at 75 °C; (2) Ambient air drying at 25 °C; and (3) Freeze drying. The dried hemp was then cured in sealed glass jars or mylar bags in dark conditions at ambient temperatures. The drying time, overall cannabinoid contents, decarboxylation level, color metrics and total aerobic loads were experimentally determined. Hot air drying can reduce the hemp moisture from 77% to safe-storage level of 6% within 8 h, and achieved up to 2-log reduction in the total yeast and mold counts. The drying time required for ambient air drying and freeze drying were 1 week and 24 h, respectively. Curing led to a 3.3% to 13.6% increase in hemp moisture, while the influence of curing method was not significant. Both drying and curing did not significantly affect the total cannabinoid contents, but resulted in decarboxylation, and reduction in the greenness. The findings suggested that hot air drying followed by glass jar curing is preferred for higher drying efficiency, better preservation of the cannabinoids and microbial safety.