Preferably, decarboxylation is carried out in a multi-step heating process in which the plant material is:
i) heated to a first temperature for a first (relatively short) time period to evaporate off retained water and allow for uniform heating of the plant material; and
ii) the temperature is increased to a second temperature for a second time period (typically longer than the first time period) until at least 95% conversion of the acid cannabinoids to their neutral form has occurred.
Preferably the first step is conducted at a temperature in the range of 100° C. to 110° C. for 10–20 minutes. More preferably the first temperature is about 105° C. and the first time period is about 15 minutes.
If the plant material is derived from cannabis plants having a high CBD content (defined as >90% CBD as a percentage of total cannabinoid content), the second temperature is preferably in the range from 115° C. to 125° C., preferably about 120° C. and the second time period is in the range from 45 to 75 minutes, preferably about 60 minutes. More preferably the second temperature is in the range from 135° C. to 145° C., preferably 140° C. and the second time period is in the range from 15 to 45 minutes, preferably about 30 minutes. In another embodiment, most preferred for a mass of plant material greater than 4 kg, the second temperature is in the range from 140° C. to 150° C., preferably 145° C. and the second time period is in the range from 55–90 minutes. The latter conditions are preferred for processing amounts of, for example, 4–6 kg of starting plant material and the exact figures, particularly time, may vary slightly with increased mass.
If the plant material is derived from cannabis plants having a high THC content (defined as >90% THC as a percentage of total cannabinoid content), the second temperature is preferably in the range of 115° C. to 125° C., typically 120° C., and the second time period is preferably in the range of 45 minutes to 75 minutes, typically about 60 minutes. More preferably the second temperature is in the range of 100° C. to 110° C., typically 105° C., and the second time period is in the range of 60 to 120 minutes. In another embodiment, most preferred for a mass of plant material greater than 4 kg, the second temperature is in the range of 140° C. to 150° C., preferably 145° C., and the second time period is in the range of 45 to 55 minutes.
Most preferably the decarboxylation step is conducted at temperatures and for times which ensure at least 97% conversion of the acid cannabinoids to their neutral form, whilst ensuring thermal degradation of THC to CBN is less than 5%.