Does Cannabis Really Need to Be Cured?

After drying, cannabis flowers are often kept in closed containers for a period known as curing. Growers commonly report changes in aroma, texture and perceived smoothness during this stage. Moisture redistribution is well supported, but explanations involving chlorophyll removal, carbohydrate breakdown or increased potency have a much less complete experimental basis.

Controlled curing can be useful, particularly for evening out moisture after drying. It is not a substitute for adequate drying, and current evidence does not establish a curing period that every cultivar must undergo.

Drying and curing describe different stages

Drying removes water from freshly harvested flowers to restrict microbial growth and prepare the material for storage. Curing is the subsequent period of controlled early storage, usually in a closed container, during which moisture redistributes and slow chemical changes continue.

Flowers that remain too wet can support mould growth after sealing. Putting them in a jar does not turn insufficient drying into a curing process, nor does later moisture control remove contamination that has already developed.

Water activity before curing

ASTM D8197-22 specifies a target water-activity range of 0.55–0.65 aw for dried cannabis flower. Below this range, flowers become increasingly brittle; above it, microbial risk increases. The drying endpoint therefore needs to be assessed from the condition of the material rather than the number of days since harvest.

Water activity describes the potential for microbial growth, not the presence or absence of contamination. Reaching a target range does not prove that a sample is microbiologically safe. Material with excessive available water needs further drying rather than prolonged storage in a closed container.

Moisture redistribution during early storage

A flower does not dry uniformly. Exposed surfaces lose water faster than the interior, and moisture can move between wetter and drier regions after the material is placed in a container. As the flower approaches equilibrium with the enclosed air, its texture may become more consistent.

Baek, Grab and Chen (2025) examined two cannabinoid-type hemp cultivars, Hempress and Wild Bourbon, using three drying treatments followed by three weeks in glass jars or Mylar bags. Flower moisture changed during curing, and some samples gained moisture. This illustrates why curing should not be treated simply as continued drying: the outcome depends on the starting material and surrounding humidity.

The study provides useful evidence for those cultivars and treatments, but does not establish that every high-THC cultivar or home-curing method will respond identically.

Chlorophyll and changes in colour

Chlorophyll degradation after harvest is a plausible contributor to changes in plant material, but the common claim that cannabis must be cured primarily to remove chlorophyll is not well established by direct experimental evidence.

In the 2025 experiment, most of the loss of green colour occurred during drying. Subsequent curing produced only small colour changes, which were generally not statistically significant. Colour measurements are not direct chemical measurements of chlorophyll breakdown, so these observations cannot determine how much chlorophyll was degraded or whether that explains a perceived change in flavour.

Sugars, starches and proposed biochemical explanations

Another familiar explanation attributes smoother smoke to enzymes or microorganisms breaking down residual sugars, starches and chlorophyll. This account appears in cultivation literature and reviews, but repetition does not establish the underlying mechanism.

The 2025 curing experiment did not directly measure carbohydrate breakdown and identified a need for further biochemical research. Carbohydrate degradation should therefore be presented as a proposed explanation rather than an established account of what conventional cannabis curing achieves.

Cannabinoid conversion is not new cannabinoid production

Cannabis produces cannabinoids largely in acidic forms, including THCA and CBDA. After harvest, these can gradually decarboxylate to neutral forms such as THC and CBD. In the three-week hemp experiment, some conversion occurred, but decarboxylation under mild curing conditions was generally below about 2% in samples that had not already undergone high-temperature drying. Total cannabinoid content did not significantly increase.

An increase in measured THC alongside a decrease in THCA therefore does not necessarily indicate an increase in total cannabinoid material. The compounds have changed chemical form. Substantial decarboxylation also occurs when material is subsequently heated during smoking or vaporisation. The experiment does not support a general claim that curing increases total potency, particularly across cultivars not included in the study.

Terpenes and perceived aroma

Aroma can change during storage without an increase in total terpene concentration. Terpenes are volatile and can evaporate, oxidise, isomerise or degrade after harvest. Long-term storage research has found declining terpene concentrations over time, rather than continued accumulation.

Moisture redistribution may influence the release of aroma compounds, while differences in volatility and chemical transformation can change their relative contributions to the smell. These are possible explanations for perceived aroma development, not proof of a single curing mechanism. A flower may smell different, or be preferred by a grower, without containing more terpenes.

The 2025 drying-and-curing experiment did not measure terpene profiles and cannot establish how its treatments affected aroma. Controlled measurements throughout conventional curing remain limited.

What is known about smoothness

Reduced harshness and improved flavour are widely reported reasons for curing. Reviews describe these benefits, but controlled sensory comparisons of otherwise equivalent cured and uncured cannabis are scarce. Grower experience can identify a meaningful preference without establishing its biochemical cause or the size of the effect.

It is therefore reasonable to describe improved smoothness as a commonly reported outcome, while keeping the mechanism and consistency of that response open. Evidence of a sensory preference should not be substituted for measurements of chlorophyll, carbohydrates or cannabinoid production.

Opening jars and controlling humidity

Opening curing jars, often called burping, exchanges enclosed humid air with the surrounding air. Its practical role is primarily moisture management. If the surrounding air is drier, opening the container can allow some moisture to leave, but this does not establish a requirement for daily fresh air as part of an essential curing reaction.

The 2025 experiment used sealed glass jars and Mylar bags for three weeks; its methods did not describe a daily grower-style burping routine. Cannabinoid content remained stable, and curing did not significantly increase yeast and mould counts under the tested conditions. However, the experiment was not a direct comparison of burping and no burping, so it cannot establish which schedule is preferable.

Once moisture is stable in an appropriate range, repeated opening may offer little additional benefit and also introduces oxygen and opportunities for volatile loss. If container humidity rises excessively, the material may have been sealed too wet. Removing it for further drying addresses that condition more directly than repeatedly opening and resealing the container. Dense flowers can develop mould internally before it is easy to see.

Curing does not sterilise flowers

Cannabis flowers can carry yeasts and fungi before harvest. Research has identified genera including Aspergillus, Penicillium, Cladosporium and Fusarium on inflorescences. Drying restricts their ability to grow mainly by reducing available water; curing should not be expected to eliminate them.

The absence of a significant increase in yeast and mould counts during controlled curing in the 2025 study does not demonstrate decontamination. Clean production, suitable drying, appropriate water activity and storage conditions remain important risk controls, but none of these alone proves the absence of contamination.

Duration and the transition to longer-term storage

There is no experimentally established curing duration that produces optimal sensory quality in every cultivar. Recommendations of two, four or eight weeks are largely cultivation conventions. Experimental work has examined three-week periods, while older recommendations often suggest approximately two weeks; neither establishes a universal endpoint.

Assessment can include moisture stability, texture, aroma and signs of microbial problems, together with the qualities the grower prefers. A lack of visible mould does not establish microbiological safety. Keeping material longer is not automatically an improvement.

In a one-year cannabis storage experiment, room-temperature storage produced greater changes in cannabinoid profiles than cooler storage, and terpenes declined over time under all tested conditions. THC can also gradually oxidise towards compounds including CBN (Milay et al., 2020). As early storage becomes longer-term storage, the emphasis shifts towards limiting unwanted change. The choice of containers and humidity-control methods belongs in that wider assessment.

Deciding what curing is intended to improve

Curing can help moisture redistribute and may be associated with sensory changes that growers value. Evidence is less complete for specific explanations involving chlorophyll or carbohydrate removal, and the recent hemp experiment did not demonstrate an increase in total cannabinoid content.

For practical purposes, begin with correctly dried material and an explicit objective, such as more consistent moisture or evaluating aroma development. Keep track of the condition of the flowers rather than assuming that a fixed period in a container necessarily improves them. Controlled early storage can be useful without being a compulsory biological stage for every harvest.

References

Baek, Y., Grab, H. & Chen, C. (2025). Postharvest Drying and Curing Affect Cannabinoid Contents and Microbial Levels in Industrial Hemp (Cannabis sativa L.). Plants, 14, 414. https://doi.org/10.3390/plants14030414.

Das, P.C., Vista, A.R., Tabil, L.G. & Baik, O.D. (2022). Postharvest Operations of Cannabis and Their Effect on Cannabinoid Content: A Review. Bioengineering, 9, 364. https://doi.org/10.3390/bioengineering9080364.

Milay, L. et al. (2020). Metabolic Profiling of Cannabis Secondary Metabolites for Evaluation of Optimal Postharvest Storage Conditions. Frontiers in Plant Science, 11, 583605. https://doi.org/10.3389/fpls.2020.583605.

Punja, Z.K. et al. (2023). Total yeast and mold levels in high THC-containing cannabis (Cannabis sativa L.) inflorescences are influenced by genotype, environment, and pre- and post-harvest handling practices. Frontiers in Microbiology, 14, 1192035. https://doi.org/10.3389/fmicb.2023.1192035.

ASTM International (2022). ASTM D8197-22. Standard Specification for Maintaining Acceptable Water Activity Range (0.55 to 0.65) for Dry Cannabis Flower Intended for Human/Animal Use. Standard specification.

Featured photograph: Dj701, Dried cannabis bud in glass cup, public domain. Reproduced without alteration. The photograph illustrates dried flower in a glass container; curing history and water activity are not established by the image.