Drying Hemp Indoors
After harvest, high CBD hemp needs to be dried in order to ensure maximum preservation and prevent deterioration of the highly valuable terpene and CBD content.
Typically, drying takes place inside of specialized drying equipment or chambers, like tobacco or seed drying units, or inside of large ventilated barns. It is very important that the drying facilities are a well-suited standard for producing medical or food products. For example, floors need to dry and clean, and there should not be any animal or insect infestation (like birds nesting overhead) that contaminate the product as it is drying.
Due to the industry's rapid growth, most farmers are using adapted or existing facilities for drying purposes. In numerous cases, they have been used previously for housing animals (like horse stables) that can potentially introduce contaminants.
Hemp plants are usually hung upside down in the form of large branches or whole plants prior to the large stems being removed from plants to be processed further.
At that time, depending on what extraction methods are preferred, the material might be ground and extracted (which includes leaves and small branches) or might be trimmed to a lesser or greater extent.
A majority of large scale processors tend to work with all of the plant material (frequently lower quality hemp). There are other processors that prefer separately processing trimmed buds in order to produce a distillate product or premium oil. Then there are other processors that take more of a middle ground approach by processing untrimmed buds which include sugar leaves but no fan leaves or stems.
Steps to Complete Indoor Drying
1. Determine Moisture Content
The industry has agreed upon a 10% moisture level for hemp to be qualified as dry. However, because hemp can sit for long periods of time in storage areas, many processors require moisture levels closer to 8-9%. It is recommended to reach out directly to your processor to align on moisture level.
Hemp is always harvested at higher moisture than what is considered safe for storage. This is to mitigate the risk of crop loss due to shattering that occurs when plants are harvested too dry. Farmers should therefore test the overall moisture content of the crop prior to harvest to determine whether immediate drying is necessary before moving to storage.
Immediate Drying (High Moisture Content)
- Use grain dryer before moving to storage when bud moisture is over 13 or 14%
Standard Interval Between Harvest and Drying (Average Moisture Content)
- Urgency is somewhat diminished when moisture content is closer to the standard 10-12% at harvest time.
- However, hemp should always be dried as soon as possible and should not be allowed to retain harvest moisture levels for more than a few hours after trimming or combining.
2. Use A Dedicated Drying Facility
Hemp plants should not be stored in the same place they are dried, as the drying process will cause buds to sweat out any dirt or other impurities that may have built up during the growing stage. This is true even for plants that have been grown inside a greenhouse or other indoor facility. Hemp must be cleaned before it is stored, and it is best to due this away from the storage site so that it may remain free of foreign debris and contaminating agents.
Maintaining a dedicated facility for drying also facilitates operational workflow. Because plants will not be stored there, space can be made available for incoming batches as dry, clean batches are moved out to be placed into storage.
3. Arrange Plants Correctly In The Drying Facility
Most hemp plants can be hung upside down as whole plants or divided into large branches to undergo drying before separation of large stems before plants undergo further processing.
However, plants intended for for CBD processing are best separated immediately prior to hanging, as this arrangement facilitates greater air flow and consequently a more even drying experience. This becomes particularly necessary when dealing with large plants or stems carrying thick, dense buds.
4. The Drying Process
Several options are available for large scale machine drying. Some of these machines use excess heat, which could potentially degrade the cannabinoids and even vaporize the terpenes, so much care and research should be done prior to financially committing oneself to a particular setup. We cover machines and equipment in more detail in our general How To Dry Hemp article, but to provide a high level overview of what you need to know:
Continuous Flow v. Batch Dryers
Either continuous flow and batch dryers can be used for bulk drying of hemp. However, standard batch dryers tend to pose a higher risk of overheating, causing hot spots to form, particularly in areas where flowers where less densely packed together and subjected to greater exposure to hot air currents.
Continuous flow dryers boast two distinct advantages over conventional batch dryers. First, their constant conveyor action eliminates the need to stop and start in order to refill bins for sequential batching. Second, they use circulating currents of pressurized air inside a closed chamber rather than heated air currents which run the risk of burning incoming crops
While this limitation does not impact the efficacy of the drying process, it can nevertheless slow down workflow since each newly dried batch must be given time to cool down and subsequently be checked for any overheated plant material that must be removed before the batch is transferred into storage.
Heat Levels & Monitoring
Grain dryer temperatures must be continuously monitored in order to prevent overheating of hemp buds. Overheated buds can be recognized by their dry, crumbly texture and lack of surface crystals, indicating a loss in oil quality due to scorching.
Moderate heat levels are advised, with a recommended plenum temperature of about 45 degrees Celsius in order to maintain batch temperatures at around 35 degrees Celsius. These levels will facilitate slow, consistent drying of hemp flowers with minimal loss from scorching.
5. Allow Dried Hemp To Cool
After drying, hemp flowers need to be cooled to ambient room temperature before baling can be commenced. This is particularly true when drying is done in facilities that do not have or cannot accommodate continuous drying systems. Ventilation at room temperature with a rate of 0.6 to 0.8 m3/min/ton will typically suffice.
When bin depth is in excess of 1.5m, air pressure must also be calibrated to improve penetration. A setting of around 2.5-5cm W.G. is well tolerated and generally effective. Fine tuning can be applied as needed once familiarity with the equipment is established.