Hemp Processing (Post Harvest Processing)
Post Harvest processing is the immediate agricultural processing of wet and dried herbal material needed to prepare the hemp for industrial, food or medical use.
Hemp Post Harvest Handling Facilities are an essential and often neglected part of the supply chain for medical hemp for CBD manufacture.
Because the hemp industry is still young and growing, many new operators lack suitable equipment, infrastructure and systems to deliver a quality product.
Industrial hemp processing (for fibre, seed and oil) is experiencing a renaissance as growers rediscover 100 year old technology and innovate new equipment, products and processes to create a 21st century hemp industry.
Whether processing hemp for industrial use or for CBD extraction, the same basic steps of post harvest handling are required.
Processing standards and equipment for Industrial Hemp Processing and Medical Hemp Processing are compared and contrasted below.
Industrial Hemp vs High CBD Medical Hemp differences
High CBD Medical Hemp is a type of Industrial Hemp specially selected to produce large amounts of high CBD, low THC resin for use in CBD (Cannabidiol) manufacture for the production of medicines.
Processing practices and equipment vary significantly depending on the variety of hemp grown, the cultivation style, the available equipment and standard processes in the region. Because of the newness of the industry, different farms and different regions often develop unique approaches and technology.
A key point to understand when developing processing solutions for industrial vs medical hemp is that even though both plants are the same species (Cannabis sativa) they are grown and handled very differently. A good analogy is Canola vs Broccoli – both are the same species but have been selected for hundreds of years to produce a particular crop. Canola (rapeseed) is an oilseed crop, whereas broccoli is a flower head crop from widely different varieties of the same plant.
Likewise in hemp – some hemp varieties are cultivated for oil seed, some for food seed, some for fibre, and others for the resin component of the flowering heads. Many varieties are dual-purpose or multi-purpose crops which allow harvest of seed, fibre, and then finally processing of the hemp biomass for CBD.
Industrial Hemp Cultivation Style
When growing hemp for seed or fibre plants are grown close together which encourages long, straight stems and abundant seed production. Male plants are desirable to maximise seed formation (and males are good for fibre as well). Plant spacing is often 10cm (4 inches) spacing or even less, resulting in dense stands of tall, straight plants, looking almost like a crop of corn, sorghum or sugarcane.
High CBD Hemp Cultivation Style
High CBD Hemp grown for medical use is best grown using purpose-bred genetics following suitable husbandry practices.
Unlike true industrial hemp, which has been selected for fibre and seed production, high CBD medical hemp should produce maximal flower and resin production.
This requires resin rich, drug-type genetics – albeit low in THC.
High CBD Hemp Cultivars
High CBD Hemp Cultivars exhibit the most desirable characteristics for the production of hemp derived-cannabinoid medicines.
The plants generally look, grow and smell more like a marijuana plant than an industrial hemp crop.
They are also cultivated to specific practices to ensure quality and maximise medicinal value and are often referred to as Medical Hemp to differentiate them from seed/fibre cultivars of industrial hemp.
Most of these strains are bred from higher CBD varieties of industrial hemp varieties with decent flower and resin production, which are then crossed high CBD medical cannabis varieties to boost potency and drug type phenotype characteristics. Sometimes these plants retain good seed/fibre characteristics, but these components are often discarded during manufacture, or are not of the standard of dedicated and dual purpose seed/fibre hemp cultivars.
The ideal medical hemp cultivar will produce large crops of abundant flower heads with good high CBD resin production, while growing well outdoors in a range of weather events such as wind, hail, frost or drought.
The quality of these outdoor flower crops should be comparable to that of a food crop, medical marijuana or recreational cannabis – after all – this is going to be used to manufacture medicine.
There is a significant flower for high quality flower which is used to produce products such as herbal teas and smoking products. For example in Switzerland there is a large market for high CBD hemp cigarettes (with up to 1% THC) and similar markets are developing elsewhere. Premium grade high CBD hemp flower may cost 5x to 10x more than most hemp flower which will only be used for extraction.
High CBD Hemp Genetics and Plant Breeders Rights Issues
High CBD Hemp Genetics are beginning to be better understand now that cannabis is legally easier to study. Key considerations include ensuring that the supplier of the hemp has the rights to use the genetics. Some strains have plant breeders rights and prohibit use of the seed or clones for production. If this is not in order the farmer may be using stolen genetics then the product may not be their to sell.
Ensuring that the CBD:THC ratio of the plant and other characteristics relevant to processing such as harvesting and processing requirements is important to plan for, and should be consistent within a cultivar.
For medical end uses, especially for full spectrum CBD products, a known genetic source, cultivar and processing method is required to meet GMP consistency requirements.
Industrial Hemp Harvesting
Industrial hemp is harvested by specially modified harvesting equipment such as combine harvesters. These machines cut down the hemp plant at the base, cut off the flowering head for flower/seed processing and sort the stalk for fibre processing.
Medical Hemp Harvesting
In contrast, high CBD medical hemp is typically harvested by hand. High CBD hemp is typically harvested by hand to ensure the flower heads are kept clean and intact and that the resin-rich trichomes aren’t dislodged by rough handling.
Hemp Drying and Storage
Drying hemp post-harvest is the most important step as it determines the ultimate product quality.
If hemp is dried quickly, cleanly and with minimal damage or loss of the product it maximises the quality of food, medicine or fibre products from the harvest.
In contrast, hemp that is harvested too wet, or dried too slowly, or with inadequate ventilation, or gets dirty or contaminated by fungi or bacteria during harvest and drying may become spoiled, unsaleable and totally unsuitable for food or medical processing.
Farmers wanting to enter the hemp industry often fail to adequately plan and prepare their drying facilities.
Hemp Processing for Fibre Production
When producing hemp for fibre harvesting begins when plants are between early bloom and seed-set and is carried out carefully to ensure that stalks are not damaged during harvest.
Harvesting was historically done by hand but new modified equipment allows hemp fibre harvesting by machine.
After harvesting, the different components of the hemp plant stem must be separated – particularly the valuable fibre and inner core, or bast.
This is achieved using a machine called a decorticator which separates the fibre from the rest of the stem. To make this easier, the fibre is typically retted to soften and separate the fibre before decortication.
Retting may be carried out in several ways with varying time, cost and quality outcomes
- Field retting or dew retting uses environmental moisture to soften the fibre over several weeks.
- Water retting softens fibre by water immersion
- Chemical retting uses chemicals to accelerate fibre separation
- Green retting uses a mechanical process to separate the plant components
The retting process has a big impact on the quality and end uses of the fibre produced. The retted fibre is then dried to 10-15% moisture for further processing.
Some modern decorticators can also work with freshly harvested material and use post processing to remove resins and gums from the fibre.
Obviously for hemp for fibre to be used for CBD extraction, the flower heads must be removed prior to fibre processing.
Hemp Processing for Seed Production
When growing hemp for seed production harvesting begins approximately six weeks after flowering or when the seeds have ripened.
Hemp seeds can be harvested with a combine harvester and many different groups are developing and testing new equipment to improve this process.
Hemp is an inherently challenging plant to work with as the resin is stick and fibre can jam machinery, often requiring manual cleaning during operation.
To ensure maximum yields from hemp seed crops the mature flower heads must be handled carefully.
- Seeds should be mature and plant material dry at the time of harvesting
- Seeds should be carefully separated from flower heads and other plant material
- Harvested seeds must be handled carefully to prevent damage, including when transferring seed.
- Use of conveyors and other low-impact transfer mechanisms are appropriate
- Machinery such as augers which could damage seed should be run at low speed to prevent damage.
- Each batch of seed should be sampled separately to ensure maturity, quality and moisture content are appropriate for storage.
Once seed has been removed the remaining plant material may be extracted or pelletised for further use.
Pelletised Hemp Biomass for Extraction
When processing seed crop or fibre crop hemp plants for CBD after seed separation, the remaining plant material (especially the leaves and flower heads) can be extracted directly, or more often, pelletised for extraction at a separate facility. Note that while regulations dictate that CBD may only be extracted from stalk and seed – these components contain negligible seed. Almost all the CBD in the plant is in the flower heads, followed by a smaller amount in the leaves.
Pelletised hemp biomass is a waste product from hemp fibre and seed production, and has many uses such as animal feed, bedding or an absorbant. Currently due to the unmet demand for CBD this material is sometimes processed for CBD extraction – often via “grey” channels that aren’t legal. For example, in 2018 Canadian pelletised biomass was widely used for CBD extraction and isolation.
This approach poses serious quality issues – pelletised biomass has rarely been grown or handled appropriately for the production of a food product. Such material may often be contaminated with soil, mold, fungi, bacteria, heavy metals, pesticides and other farm chemicals.
High CBD Hemp for Medicinal Use
High CBD hemp is cultivated and handled specifically for the production of CBD extracts and hemp-derived medicines.
In contrast to fibre and seed hemp crops, high CBD hemp is grown as a female-only crop, with wide plant spacing (4-8 foot spacing is common).
Plants are typically individually irrigated and managed. While self-staking varieties are preferred, larger plants may require training, staking or supports as their flowers grow and mature, particularly if weather is challenging. Cultivation style and varietal selection appropriate to the environment are critical.
High CBD Hemp Harvest Timing
Plants are harvested when flower heads are fully mature and beginning to ripen and dry. Tests for THC and CBD levels in leaves and flower head moisture levels also guide plant harvest schedules. These may be combined with or complement THC testing required by regulators.
High CBD Hemp THC Testing
Due to the controlled nature of hemp and other Cannabis plants, hemp requires testing during cultivation to ensure it’s THC levels don’t exceed legally specified limits.
In many regions, most strains must be harvested before fully mature to prevent THC levels exceeding legally prescribed limits (typically 0.3% THC). Plants that exceed this level are termed hot and their detection can require destruction of the crop. Specific guidelines on testing and harvest requirements are subject to local or state regulation and advice – typically via the State Department of Agriculture.
High CBD Hemp post harvest processing
After harvest, high CBD hemp must be dried to prevent deterioration and ensure maximum preservation of the valuable CBD and terpene content.
Drying typically occurs inside large ventilated barns or specialised drying chambers or equipment, such as seed or tobacco drying units. It is important that these drying facilities are of a suitable standard for production of a food or medical product. For example floors should be clean and dry, and there should be no insect or animal infestation (such as birds nesting overhead) which could contaminate the drying product. Due to the rapid growth of the industry much of the industry is currently using existing or adapted facilities for drying. In many cases these have previously been used to house animals (such as horse stables) which introduces potential contaminants.
Hemp plants are typically hung upside down as whole plants or large branches before the large stems are removed from the plants for further processing.
At this time, depending on the preferred extraction methods, the material may be ground and extracted (including small branches and leaves) or may be trimmed to a greater or lesser extent.
For example most large scale processors work with the entire plant material (often of lower quality hemp). Other processors prefer to process trimmed buds separately to produce a premium oil or distillate product. Other processors take a middle ground and prefer to process untrimmed buds including sugar leaves but no stem or fan leaves.
Hemp Storage and Distribution
Hemp for use in food or medicine manufacture should be stored in appropriate facilities that allow control of temperature, humidity, light and hygiene to ensure potency, purity, and cleanliness of the product and packaging can be ensured.
Each individual batch must be properly labelled and located to prevent mixing of batches.
Storage and distribution facilities should incorporate areas for quarantine, storage and release pending testing, buyer approval and shipping orders.
During loading, transit and distribution the product should be stored under comparable conditions to ensure the quality and integrity of the product is maintained.
Hemp Processing Standards
As the hemp industry matures and becomes better regulated, manufacturing and quality assurance standards from other industries help inform best practice.
Rhizo Sciences draws on international quality systems such as GAP (Good Agricultural Practice), GMP (Good Manufacturing Practice) and GDP (Good Distribution Practice) when developing new facilities and processes. Food grade and other agricultural standards such as organic certification may also be relevant.
We aim to develop a full suite of GxP systems for our supply chain over the coming 18 months as the hemp industry evolves.
Hemp Processing to Extract CBD
After hemp has been harvested, dried and processed it is ready to send to a CBD processing facility to extract the CBD rich hemp oil from the flower or biomass material. After initial extraction of the crude CBD rich hemp oil, CBD is further refined to produce CBD distillate or CBD isolate which are then sold or processed into finished CBD medicines such as oil tinctures or capsules.