Hemp Storage Services

The Drying & Storage Stage

Hemp must be dried and stored immediately after it is harvested. Because of this, drying and storage are often treated as two parts of the same post-harvest operation. Yet while there is some procedural overlap between the two, these operations are perhaps better understood as two distinct phases in the overall production process. There are a number of reasons for this.

First, the operations have distinct goals. With drying, the focus is on product preparation, while storage aims at long-term product maintenance pending approval and delivery to the processor.

Second, drying and storage are always done in different facilities using separate equipment, even if some tools, such as aeration systems, may be used during both phases.

Thirdly, the timeframes are different. Drying must be initiated within a few hours of harvest and has a maximum timeframe of 7-10 days, while storage may require a period of up to two years depending on the processor.

In this guide, we present an overview of best drying practices for hemp flower and biomass.

1. DRYING

Hemp is always harvested at a higher moisture content than is safe to put into storage in order to prevent shattering loss during trimming or combining. For this reason, it should always be dried as soon after harvest as is practicable. Sometimes, when moisture content is particularly high, it should even be dried immediately after harvesting.

1. DRYING METHODS

1) Outdoor drying (Drying on the vine)

Natural Approach

Deceptively less labor intensive but leaves a lot to chance (even if uncertainties can be minimized with sufficient knowledge, it’s never a sure thing and drying may be inconsistent, especially on dual variety farms)

2) Drying in a Facility

Typically done inside a barn used exclusively for drying crops

If possible, dry hemp in its own dedicated facility to avoid contamination through contact with other crops

If total isolation is not possible, clean thoroughly to remove residual matter from previous crop, especially wheat if crop is to qualify as food grade hemp (Food grade hemp must be certified gluten free)

NOTE: Doesn’t apply to farmers growing exclusively for industrial fiber or biomass)

Using Both Methods

Indoor & outdoor methods can be combined, especially in single-variety fields

Each method will require its own set of tools, although strict line drying requires minimal tool usage, whereas indoor drying is done specifically so the operation can be carried out in its own dedicated space designed (or at least suitable) to facilitate the use of large-scale industrial agricultural equipment.

1. HEMP DRYING EQUIPMENT

1. Commonly Used Equipment

Throughout the industry, batch and continuous flow dryers are presently the most commonly-employed solutions for drying hemp at industrial scale.

Both machines have long histories of reliable use in the grain industry and will likely remain the go-to option for many emerging hemp farmers, as well as for veteran grain farmers who are now crossing over into hemp production.

Even so, alternative methods do exist, as do many novel solutions designed with the specific needs of the hemp farmer in mind. Below is a sampling of some of the available options.

1. Commonly Used Hemp Drying Equipment

Batch Dryers

A drying solution that is nearly ubiquitous in the wheat industry, these large-scale drying machines can rapidly dry large quantities of freshly cut hemp and can easily keep pace with a rigorous combining schedule. Accelerated heating takes place towards the end of the drying cycle as heat builds up inside the bin, which can cause overheating when applied too hemp. Hence, while they present a powerful option for speedy drying some care and practice are required to determine appropriate heat staging to minimize the risk of burning the bin contents.

Continuous Flow Dryers                                                                                

Continuous flow dryers enlist the use of a double conveyor belt system, where one conveyor continuously feeds the drying mechanism with incoming plant matter and the other turns out the finished dried product.

These devices are a favorite among farmers across many Industries due to their high throughput capacity.

In the case of hemp flowers they have been shown to churn out an impressive 1000 lbs damp plant matter per hour.

Conveyor Belt Dryers

Similar to continuous flow dryers, conveyor belt dryers also allow for constant throughput of combined plant matter, except that these systems employ heating drums rather than pressurized airflow chambers to affect desiccation. Drums are available in multiple sizes, providing an adaptable solution that can be scaled with operations at minimal cost. They are particularly well suited to farmers who must dry large quantities of very moist hemp flowers for which conventional continuous flow dryers may not prove as effective.                                                                                 

Grain Drying Fans                                         

A simple, cost-effective solution that can be used as a standalone in conjunction with that dryers or other drying systems.

It should be noted that drying through direct application of air current is necessarily less efficient than drying inside a closed chamber, as a strict fan-based setup does not allow for channeling of air currents into concentrated streams that would speed up the drying process. They may however prove ideal for new farmers who do not yet possess the budget to invest in industrial scale solutions.

Farmers who tough-harvest their hemp crop — that is, harvest by hand — may also find an appealing option in a well-placed array of drying fans that can apply constant airflow to freestanding bins while subsequent loads are being harvested.                                                                                                     

AC Units

As with drying fans, conventional air conditioning units can be employed as a standalone solution so long as units are sufficiently powerful to dry the targeted quantity of hemp flowers. However, their optimal use case scenario is to play a supporting role in long-term aeration during storage, and for the cooling of freshly dried hemp flowers, to bring them to room temperature before bailing for storage.

Traditional Hang Dryers                                             

Specifically intended for use in cool, dark storage areas where whole-harvested hemp plants are to be dried in bulk. These drying systems offer both temperature and humidity control settings.

In the case of hemp, a temperature setting of around 65 degrees Fahrenheit (18 degrees Celsius) and about 62% humidity has been found to be effective for some farmers.

2. Novel Hemp-Specific Drying Equipment

Mesh Hemp Belt Drying Machines

Designed for use by multi-cultivar hemp farmers who require more nuanced control over the drying process than is typically afforded by conventional grain drying equipment, these systems employ multiple physically isolated drying chambers, each with its own internal hot air circulation system and exhaust fanfor moisture filtration.

Temperature and drying time can be adjusted individually for each chamber, allowing for concurrent drying of separate flowers batches with varying moisture contents. This level of control eliminates the need to recalibrate settings for each incoming hemp batch.

Portable Hemp Dryers                                                                       

These newcomers to the scene purport to possess the capacity for drying up to 75, 000 lbs of plant material per hour.

Independent testing and research have yet to be done to verify these claims and anecdotal reports are sparse at present.

Nonetheless, it may be worth keeping an eye on these and similar devices slated to hit the market soon. Intrepid farmers may wish to test out such equipment themselves, especially if the manufacturer offers a rental or trial period.

Custom Hemp Drying Systems

These straightforward machines are designed to the individual farmer’s specifications along the lines of drum size and burner temperature, with components mounted in concurrent configuration. These systems are constructed to dry as many as eight tons of hemp per hour at an output moisture of between 10 and 12%.

It is worth noting that while these figures are certainly impressive, many hemp processors require a flowers moisture content of between 8-9% for long-term storage. Nonetheless, it is advisable to keep an eye on these options as competition drives manufacturers to strive to achieve even lower output moisture levels.

1. STEPS TO COMPLETE (OUTDOOR DRYING)
   

This method is often used prior to tough-harvesting of hemp flowers to reduce the amount of time required to batch dry after trimming or combining has been completed. Allowing the hemp plant to dry naturally on its own can be useful when desiring to jumpstart the curing process.

STEP 1: Dry Until Stems Split When Bent

Leave hemp plants hanging on the line for 3-10 until stems begin to split when bent. This will serve as a cue that the plants are dry enough to be trimmed.

NOTE: Do not allow stems to become so dry that they snap under pressure as this can lead to the loss or damage of trichomes as they will be more susceptible to flaking when casually brushed or carelessly handled.

Length of Drying Period

The exact during will depend on several factors including heat and sunlight exposure nearing the time of harvest, as well as the size of the buds to be dried.

1. STEPS TO COMPLETE (INDOOR DRYING)

STEP 1: Determine Moisture Content

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.

1. Immediate Drying (High Moisture Content)

Use grain dryer before moving to storage when bud moisture is over 13 or 14%

1. 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.

STEP 2. Dry Before Storing

It is very important that harvested plant material is dried before being moved to storage. Hemp seeds and flowers heat and expand very rapidly after being removed from the vine causing leaves and buds to sweat. This causes pockets of condensation to build up inside the bin, leading to mold growth. Because hemp flowers tend to clump as they heat, fatty acids can quickly build up inside the oil, causing it to lose potency or even turn rancid through fermentation and bacterial exposure if left unattended for too long.

Naturally, heated or moldy buds will be rejected by the processor as they will fail to meet strict purity standards required for food grade labeling.

STEP 3. 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.

STEP 4: 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 medicinal use 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.

STEP 5: 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.

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.

STEP 6: Allow Dried Hemp To Cool

Cool After Drying

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.

Target Moisture Content

The industry has agreed upon a 10% moisture level for hemp to qualify as dry. However, because hemp destined for the marketplace can sit in storage for as much as 1-2 years before being shipped out for processing, many processors require storage moisture levels closer to 8-9%. It is best to consult the processor well in advance of harvest to ascertain what they consider safe for long-term storage.

STEP 7: Clean Hemp Flowers Before Baling

1. Outsourcing Drying Operations

This is a third option for new and small-scale farmers who do not yet have on-site facilities required for large scale hemp production, or for those desiring to produce smaller yields and for hobbyists.

One possible downside for next few years is price. Hemp is booming. Everyone    wants in, and drying facilities will continue to remain in high demand until the market stabilizes.

These services often tend to be highly regional, and there is no guarantee that they may be available in any given state or locale.