What happens to terpenes when cannabis is dried?

Drying is a chemical step, not a removal of water, and the terpene profile that leaves the drying room is not the one the plant made. Across independent studies the direction of the shift is the same, though its size depends on the chemovar. Light monoterpenes are the fraction at risk, sesquiterpenes rise in relative concentration, and the total moves up or down depending on which quantity the laboratory reported. Temperature and exposure time both drive the loss, so a maximum temperature alone does not describe a process. Freeze drying protects the acid cannabinoids and damages the light volatiles, which makes it a trade rather than an improvement. For a quality unit the practical consequence is narrow and useful. A terpene result is comparable only when the report states the metric, the sampling point in time and the drying conditions that produced the material. Without those three, two certificates from the same cultivar can disagree for reasons that have nothing to do with the plant.

Both answers appear in the literature because the two studies measure different quantities. Chen and co-workers (2021) report total terpene retention against the fresh material falling from 82.1 per cent to 29.9 per cent as the drying temperature rises from ambient to 90 degrees, with drying time compressed from 1800 to 210 minutes. Birenboim and co-workers (2024) report total terpene content, monoterpenes and sesquiterpenes together, increasing by roughly 25 to 30 per cent during drying. The second figure is a concentration on dry weight, measured on a matrix whose mass has changed. A site that shows stable or rising terpene percentages after drying has not demonstrated that nothing was lost. It has measured a ratio whose denominator moved.

It is the most consistent result in the drying literature, and it carries a condition worth knowing. In the high-THC chemovar studied by Birenboim, beta-myrcene lost roughly 3 to 20 per cent of its initial concentration, alpha-pinene and d-limonene stayed stable, and every sesquiterpene rose by 20 to 50 per cent in relative terms. Wanas and co-workers (2020) found the same shift in the ratio of sesquiterpenes to monoterpenes on air-dried buds, with terpinolene dramatically reduced, but only in the high-THC chemotype: in their intermediate and high-CBD chemotypes drying produced no detectable change in either fraction. The chemotype decides whether the shift appears at all, which is itself a reason not to carry one supplier’s drying data over to another. Where it does appear, storage repeats it, since Birenboim’s preservation study found sesquiterpenes less susceptible to degradation than monoterpenes over four months. The consequence for a specification is direct. A stable total can hide a monoterpene loss that a rising sesquiterpene fraction has offset.

Both, and the pair matters more than either number alone. The temperature effect is monotonic in the only complete curve available, the one Chen published. Time carries comparable weight. Uziel and co-workers (2024) quantified 36 terpenoids and found that solid-state microwave drying at 50 degrees preserved the composition of the secondary metabolites better than traditional drying at 16 degrees and 50 per cent relative humidity run for 10 days. Cold is not automatically safe when exposure lasts a week and a half. An audit cell that records only a maximum drying temperature is built on the wrong variable, because the same figure can sit above two processes with very different outcomes.

Not the volatile fraction. Spadafora and co-workers (2024) compared tray drying at 18 degrees with freeze drying and found that of the 45 compounds affected negatively, 28 belonged to the terpene group. The most affected list includes beta-myrcene, alpha-pinene, d-limonene and terpinolene, and the same authors note that these four contribute up to half of the aroma of cannabis. Their conclusion is explicit, since freeze drying preserves the cannabinoid content and prevents decarboxylation of the acid cannabinoids while leading to a loss of volatile compounds. Where a site justifies freeze drying as a terpene preservation measure, the justification is not supported by the literature. Controlled atmosphere drying is the approach with a measured advantage on volatiles, and Birenboim found the optimal conditions to be chemovar specific.

Three fields turn a terpene number into evidence. The metric, stated as retention against fresh material or as concentration on dry weight. The time point, since a result taken after curing describes a different material from one taken at the end of drying. The drying conditions, meaning temperature, relative humidity, air movement and duration together, which are what the EMA guideline on Good Agricultural and Collection Practice places under primary processing. A fourth field is worth requesting even though no study validates it as a release parameter, the ratio of monoterpenes to sesquiterpenes, because it moves when the process moves and a total does not. The same discipline applies wherever the boundary between agricultural and pharmaceutical rules sits, which we covered in where GMP begins for an active substance, and our review works through the metric before the number across the whole drying literature.

Written by

Riccardo Longato

GMP Pharmaceutical Quality Systems Lead Auditor

CQI/IRCA certified lead auditor, certificate no. LA113.

Has spoken at PTMC Lisbon, JIHE Tokyo, AIHEF Bangkok and IndicaSativa Trade Bologna.

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