The quality of medicinal cannabis depends not only on the growing conditions but also on the processes applied after harvest. Recent studies have shown that post-harvest handling techniques can significantly affect the concentration of cannabinoids in cannabis inflorescences.
A study titled ‘Effects of postharvest manipulation on cannabinoids in cannabis (Cannabis sativa L.) inflorescences’revealed that cannabinoids are not only lost through volatilization but also through the handling of the flowers, as glandular trichomes can detach with the slightest touch.
The role of trichomes in cannabinoid loss
Trichomes are microscopic structures on the surface of cannabis flowers that contain cannabinoids, terpenes, and flavonoids. They are extremely sensitive to physical handling as they are easily damaged due to their delicate structure.
In the study, it was observed that even gentle handling of the flowers caused a significant portion of the trichomes to fall off, resulting in a direct loss of cannabinoids. Additionally, it demonstrates how different handling methods (e.g., wet or dry trimming) affect the integrity of the trichomes. Wet trimming (before drying) resulted in a higher loss of trichomes because the flowers still contained high levels of moisture, making them more vulnerable to physical damage.
In contrast, dry trimming, where the flowers are already dehydrated, showed less trichome loss, but also had the disadvantage of less controlled drying, which could result in increased cannabinoid volatilization.
Trimming: before or after drying?
One of the first post-harvest decisions is whether to trim before or after drying. Both methods have advantages and disadvantages in terms of cannabinoid retention.
- Trimming before drying (wet trimming): In this case, the leaves surrounding the buds are removed before the cannabis dries. This process is done when the flowers still have a high moisture content. The advantage of this method is that the leaves are removed quickly, allowing the buds to stay fresh and aesthetically appealing. However, the flowers may become more vulnerable to handling, which could result in the loss of trichomes.
- Trimming after drying (dry trimming): Here, the flowers are allowed to dry first, and then the leaves are trimmed. This method may be gentler in terms of preserving the trichomes, as the flowers are drier and the trichomes are harder to detach. However, the drying process can lead to accelerated degradation of cannabinoids, especially if done in conditions of heat or high light exposure. Despite this, dry trimming is popular among growers because it may result in better terpene retention, which is crucial for the aroma and flavor of cannabis.
Drying techniques and their effect on cannabinoids and terpenes
The drying process is one of the most critical factors in preserving cannabis quality. If not done properly, it can result in the loss of cannabinoids and other volatile compounds. Drying methods include:
- Hot air drying: This is the most common method but also one of the most impactful on the loss of cannabinoids and terpenes. If drying is done in an environment with excessively high temperatures or excessive air circulation, significant evaporation of volatile compounds can occur. Additionally, cannabinoids like THC can be converted to their acidic form, THC-A, which reduces their psychoactive potency.
- Freeze drying: Freeze drying involves rapidly freezing the flowers followed by a sublimation process. This method is much more efficient in preserving cannabinoid potency because it minimizes exposure to heat and oxidation. However, while cannabinoids are optimally preserved, terpenes may be compromised, affecting the taste and aroma of the cannabis.
- Tray drying: This method is an intermediate option where the flowers are placed on trays with controlled air circulation. It allows for uniform drying at lower temperatures, helping preserve both cannabinoids and terpenes. The key here is controlling temperature and relative humidity during the process to prevent the flowers from dehydrating too quickly or being exposed to unfavorable conditions.
Oxidation of terpenes, which occurs when flowers are handled in environments with excess oxygen, reduces not only the flavor but also the complete cannabinoid profile. Loss of terpenes such as limonene, myrcene, and pinene interferes with the entourage effect between cannabinoids, a phenomenon where terpenoid compounds enhance the effects of cannabinoids. As a result, a significant loss of terpenes can reduce the therapeutic efficacy of cannabinoids, making the cannabis less effective in medical treatments.
Effects of temperature and oxidation
On a chemical level, THC and CBD are made up of carbon and hydrogen chains that can react with oxygen or heat, leading to the degradation of their molecular structure. In particular, THC is converted into CBN (cannabinol), a cannabinoid with much lower psychoactive effects, while CBD oxidizes to form CBDV (cannabidivarin), which is less potent.
High heat during the drying process can induce a reaction called decarboxylation, where the cannabinoid precursors (such as THC-A and CBD-A) lose a carboxyl group (CO2), turning the acids into their active forms, such as THC and CBD. Excessive temperatures can not only accelerate decarboxylation but also destroy active compounds before they are converted into their ideal forms for consumption.
For example, THC-A converts to THC at temperatures between 60°C and 70°C, but if the temperature exceeds 80°C, the conversion becomes less efficient, and THC oxidizes quickly into CBN. This thermal degradation process is one of the main reasons why rapid or poorly controlled drying can result in a significant loss of potency in the final product.
Curing: the final touch to enhance potency
After drying, curing is one of the most important stages in producing high-quality cannabis. Curing allows cannabinoids to settle and mature optimally. During this phase, terpenes stabilize, and cannabinoid potency intensifies, while undesirable compounds like chlorophyll are eliminated.
The curing process should be done in airtight containers, such as glass jars or sealed containers, to prevent moisture loss and allow slow decomposition of compounds over several weeks.
Microclimates during curing
Another technical aspect is the interaction of enzymes in cannabis during the curing process. Cannabinoids in their acidic form (such as THC-A) are in an inactive state, but the natural enzymes present in cannabis can facilitate their conversion into active forms during curing.
If the curing environment is too warm or humid, enzymes may accelerate the conversion into inactive or undesirable forms. According to the chemical theory presented in the study, enzymes such as decarboxylase are important in the transformation of cannabinoid acids into their active forms during curing.
The ideal environment for these reactions is one with moderate temperatures (around 20°C-25°C) and low relative humidity (40%-60%), which optimizes decarboxylation without the risk of destroying active cannabinoids.
Storage: maintaining potency and aroma
The final stage of post-harvest handling is storage. Although cannabis may be fully dried and cured, its quality will not be guaranteed if it is not stored correctly. Storage conditions play a crucial role in preserving cannabinoids and terpenes in the long term.
- Temperature: It is essential to store cannabis in a cool place, with temperatures around 4°C. This minimizes cannabinoid degradation, especially oxidation, which can reduce potency over time. Temperature also affects the preservation of terpenes, which are very sensitive to heat.
- Light Exposure: Ultraviolet (UV) light can break down cannabinoids and alter the terpene profile. Therefore, it is recommended to store cannabis in dark places or opaque containers that protect the flowers from light.
- Humidity: The correct level of humidity is crucial to prevent decomposition or mold formation. The ideal relative humidity for cannabis storage is between 59-63%. High humidity conditions can encourage mold growth, while low humidity can cause trichomes to break easily, and cannabinoids to become less effective.
3 steps to minimize cannabinoid loss during processing
- Gentle handling during trimming: Using sharp scissors and careful trimming techniques can minimize trichome damage, reducing cannabinoid loss. It is important to avoid handling the flowers roughly.
- Temperature and humidity control during drying: Maintaining a controlled environment with mild temperatures is key to preserving cannabis potency. Using tray dryers with temperature control or drying in dark rooms can significantly contribute to cannabinoid preservation.
- Optimal storage: As mentioned, storing cannabis in airtight containers and in cool, dark conditions is essential to maintain its quality. Additionally, using humidifiers or dehumidifiers in storage areas can help control humidity to avoid premature degradation.