Cannabis Drying & Curing 101
Cannabis is grown worldwide, it’s resilient, and it’s in high demand. A demand that isn’t slowing anytime soon. New amendments to the Cannabis Act will make a legal space for edibles and alternative cannabis products in Canada, with an estimated worth of C$2.7 billion annually. And that’s just in our northern-corner of the market.
With more legal producers than ever before, the demand for quality cannabis is also increasing. Consumers are no longer settling for sub-par – they want the best. High-quality cannabis starts at the strain-level, requiring investment in every step of the process. This is especially true for post-harvest care.
Cannabis drying and curing are integral in successfully moving plants from harvest to sale. In this article, we’ll differentiate between drying and curing, outlining the pros and cons of each. We’ll look at traditional methods, and touch on innovation in the industry. It’s now possible to save time without sacrificing quality, and Rapid Low-Temperature Dehydration (RLTD) technology is the answer.
The Difference Between Cannabis Drying and Curing
Many growers believe that curing begins at the moment of harvest. If that’s the case, where does drying fit in? In traditional methods, drying and curing are two separate steps, distinguished by humidity, temperature, and time. The method for harvesting is also important, impacting the order of the process.
Ready for Harvest
Cannabis buds are ready for harvest when the majority of the pistils (the small white hairs on the buds) have browned and begun to curl in. Trichomes under magnification can also be used as a tool. They will transform from clear to cloudy when it’s time to harvest.
Once the buds are ready for trimming, there are two main methods: dry trimming and wet trimming. Wet trimming occurs right after harvest when the buds are wet. The moisture makes the buds less fragile, and easier to manage quickly. Dry trimming occurs after drying, but before curing. This method is more challenging and can lead to a loss of product; however, it results in more precisely-manicured buds.
Cannabis Drying the Conventional Way
Regardless of the trimming method, harvested cannabis must be dried immediately to avoid spoilage. Most of the moisture should be removed within the first three days, then slowed to avoid drying out. The product should be kept in a dark room with air circulation, at a temperature range of 60-70°F and humidity between 45-55%.
To ensure even-drying using the conventional method, cannabis branches are hung up or placed on racks. Trimmings are hung upside-down to encourage circulation to smaller branches. In general, traditional hang drying can range from 5-15 days, depending on the size of the buds and the surrounding environment.
The most common way to determine if the drying process is complete is to test the brittleness of the smallest branches. If the small branches snap on bending, and the buds are slightly crisp on the outside, then the plants are ready for curing.
Curing has been a part of food preservation since the beginning of civilization. When most people think of curing, they think of salting meat. For cannabis, however, no salt is needed. Curing can be thought of as an extension of drying, with an altered environment to facilitate plant processes.
The first step in curing depends on whether the plant material was trimmed at harvest. If the branches still require trimming, this must be done first. The buds are then placed into airtight containers, often mason jars about three-quarters full, and sealed.
Cannabinoids are light, heat, and oxygen-sensitive. To prevent mold growth, the buds still need to breathe. In airtight containers, moisture trapped within the buds will be drawn out, creating a humid environment. The ideal humidity is approximately 60-65%, with a below room temperature and complete darkness.
During the first week, the containers must be opened throughout the day to let the buds breathe. In the weeks following, this can be limited to once every few days. Two to three weeks is sufficient for curing but waiting longer is ideal. Four to eight weeks is great for most strains, though some can benefit from even longer.
Drying and curing cannabis has a myriad of benefits. Without drying, the moisture content in buds hinders the smoking experience and can lead to mold contamination. Without curing, the flavour and aroma aren’t given time to properly develop. Much like the ageing of fine wine, cannabis will get better over time under the right conditions.
Here are some of the ways cannabis can be improved post-harvest:
- Improved potency – the biosynthesis of cannabinoids doesn’t stop immediately upon harvesting; under the right conditions, buds will keep converting cannabinoids for increased potency and quality
- Improved sensory experience – terpenes (the molecules responsible for flavour and aroma) are volatile compounds that quickly degrade; curing at low temperatures can help protect these compounds
- Smoother finish – curing helps to get rid of chlorophyll, sugars, and starches within the plant; without this removal, the smoke can be bitter and hard on the throat
- Increased shelf-life – cured cannabis can be stored for up to two years without losing integrity; without drying and curing, the potential for contamination and cannabinoid-loss increases over time.
Mold is the biggest threat to cannabis plants. Humidity is necessary for the curing process, but it also creates the perfect breeding ground for fungi and bacteria. Plant infections such as Botrytis and Penicillium bud rot are common in the industry, in small-scale and industrial-size facilities alike.
Contamination is a threat to production quality and can lead to serious health problems for consumers. For producers, there are additional challenges in using the traditional methods. These include large space requirements for drying rooms, unpleasant odours, and time and labour intensive processing.
The traditional slow-drying method can be well-suited for small-scale producers. For larger applications, the risk for contamination and the cost of operation scales-up with size. In recent years, alternative methods have been increasing in popularity, in an effort to save time, space, and production quality.
Cannabis can be quickly processed with dry-ice through freeze-drying. Temperatures below zero turn water into ice crystals, that can be converted into water vapour using low pressure. A vacuum can then be used to draw out the water vapour, leaving the plant material in its same high-quality state, minus the water.
As dry ice contains no humidity, the risk for mold contamination is reduced. On the other hand, time-consuming rehydration is often required to bring moisture back into the buds for sale. Freezing too early can also prevent the breakdown of undesirable plant compounds, and cause a more unpleasant smoking experience.
Curing with water instead of air is an alternative that enhances the smoke smoothness. In this method, buds are placed into water-filled jars before the drying process. As most of the undesirable plant compounds are water-soluble, the water breaks down these compounds, instead of the plant.
Sugars, starches, and chlorophyll diffuse into the water, while fat-soluble cannabinoids remain in the plant material. This process is much faster than traditional drying, moving plants from harvest to sale-ready in 5-8 days. While this sounds ideal, there are some challenges with this method.
Certain desirable flavour and aroma compounds in cannabis are water-soluble, and will also diffuse out of the buds. This can reduce the sensory experience in the finished product. The end-product is also less vibrant (as the green chlorophyll has diffused out), and less visually appealing overall.
Vacuum Thermal Energy Technology
Vacuum technology works by reducing pressure within a system, which lowers the boiling point of water and the undesirable compounds in cannabis. This allows for a low-temperature boiling-off, while keeping the desirable colour, cannabinoids, and terpenes in the product.
Vacuum technology pulls moisture from within the buds to the surface, where it can be dried quickly and consistently. Though speed was an enemy to drying and curing in the past, an adapted quick-dry process can actually enhance quality.
Time is the enemy of terpenes. They are volatile compounds that quickly begin to degrade after harvest. Vacuum-assisted drying allows for a faster drying at a lower temperature, where terpenes are conserved. Low-temperature dehydration facilitates drying and curing simultaneously. This eliminates the need for curing, while pampering the plant material.
Cannabis Drying with Dhydra
Dhydra technologies uses a novel adaptation of vacuum technology. With rapid drying time, production cycles are accelerated and energy consumption is reduced. The need for large drying rooms is eliminated, lowering operational costs and increasing potential yield.
Dhydra Technologies has revolutionized cannabis drying and processing by providing the industry with the capability to dry large amount of product in record times. From cut to dry (<10%) in under an hour, Dhydra’s solution can provide the owner with a fully cured product ready for packaging and distribution. Able to process 150lbs or more per hour, Dhydra is changing the cannabis landscape.
RLTD technology meets and exceeds all of the benefits of traditional drying and curing. It provides a sanitary environment, meeting Food Safety and GMP standards. With an industrial-scale capacity, this technology solves an industry bottleneck.
How it Works
By lowering the pressure, the system creased a vacuum that allows the water in the product to “boil” (water becomes vapour) at room temperature. Dhydra’s Disruptive Technology applies low thermal energy in a strictly controlled manner to generate water vapour without destroying the plants nutrients or other valuable attributes.
By heating the water, rather than the plant nutrients and attributes, Dhydra provides a superior output, including improved flavour and texture. This also allows for maximum oil extraction yields.
One Dhydra advantage is that the system targets energy into tightly defined regions. Rather than standing hot spots, Dhydra controls the travelling waves of energy allowing them to be applied evenly. This allows the energy levels to be matched to the cannabis plants drying ability. Ultimately, in a rapid low thermal processing dehydrator, the energy levels can be controlled throughout the drying process. This prevents the hemp plant from overheating.
Dhydra is the solution for rapid production and remarkable quality – bringing to market an elevated industry standard.
- “BC Agricultural Composting Handbook” (1998) British Columbia Ministry of Agriculture and Food. Retrieved from http://www.rdosmaps.bc.ca/min_bylaws/ES/solid_waste/BCAgCompostHandbook1998.pdf
- Bhadauria, T. Saxena, K.G. (2009) “Role of Earthworms in Soil Fertility Maintenance through the Production of Biogenic Structures” Applied and Environmental Soil Science. 2010. Retrieved from https://www.hindawi.com/journals/aess/2010/816073/
- Compost Tea (2019). Soil Food Web Institute. Retrieved from http://www.soilfoodweb.com.au/about-our-organisation/actively-aerated-compost-tea-information
- Islam, M.K. et al. (2016) “Effects of the main extraction parameters on chemical and microbial characteristics of compost tea” Waste Management, 52, 62-68. Retrieved from https://www.sciencedirect.com/science/article/pii/S0956053X1630126X?via%3Dihub
- Reiny, Samson. (2016) “CO2 is making Earth Greener – for now” NASA Earth Science News Team. Retrieved from https://climate.nasa.gov/news/2436/co2-is-making-earth-greenerfor-now/
- Shaban, H. et al. (2015) “An Overview of the Benefits of Compost tea on Plant and Soil Structure” Advances in Bioresearch. 6, 154-158 Retrieved from https://www.researchgate.net/publication/278242997_An_Overview_of_the_Benefits_of_Compost_tea_on_Plant_and_Soil_Structure
- “Stomate” definition provided by Encyclopaedia Britannica. Retrieved from https://www.britannica.com/science/stomate
- Trautmann, N. Olynciw, E. (1996) “Compost Microorganisms” Cornell Science and Engineering. Retrieved from http://compost.css.cornell.edu/microorg.html
- Government of Canada contributors (2018). Cannabis Act (S.C. 2018, c.16). Justice Laws Website.
- Deloitte Contributors (2019). Nurturing new growth | Canada gets ready for cannabis 2.0. Deloitte.
- Haze, N. When are Marijuana Buds Ready to Harvest? GrowWeedEasy.
- RQS (October 2019). Top Tips To Successfully Dry And Cure Your Fresh Cannabis Buds. Royal Queen Seeds.
- Felepchuck, L. (March 2019). How to dry and cure cannabis flowers like a pro. The Growth Op.
- Hutmacher, A. (February 2018). Curing Cannabis: Why It’s Important and How to Do It Properly. Pot Guide Colorado.
- Leafly Contributors (August 2016). Your guide to drying and curing cannabis buds. Leafly.
- Jin, D., Jin, S., Chen, J. (June 2019). Cannabis Indoor Growing Conditions, Management Practices, and Post-Harvest Treatment: A Review. Scientific Research 10(6):925-946.
- MarijuanaBreak Staff (July 2019). How to Dry Cannabis Flower. Marijuana Break.
- Russo, E. (July 2011). Tamping THC: potential cannabis synergy and phytocannabinoid-terpenoid entourage effects. British Journal of Pharmacology 163(7):1344-1364.
- Haze, N. & Alltatup (September 2019). Complete Drying & Curing Marijuana Guide. GrowWeedEasy.
- Punja, Z.K. (September 2018). Flower and foliage-infecting pathogens of marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4): 514-527.
- Leafly Staff (November 2017). CO2 Trimming and Freeze Drying. Leafly.
- Sherrard, M. 3 Alternative Curing Methods. Civilized.
- RQS (April 2018). Water Curing Your Weed. Royal Queen Seeds.
- CannaConnection Contributors (June 2019). Water curing of marijuana buds. CannaConnection.
- Youngblood, T. (December 2017). How Vacuum Ovens Are Used in the Cannabis Industry. Cannabis tech.
- Orsat, V., Changrue, V., Raghavan, V. (December 2006). Microwave drying of fruits and vegetables. Stewart Postharvest Review 2(6):1-7.
- Health Canada (2018). Good Manufacturing Practices. Government of Canada.