Harvesting Industrial Hemp
The passing of 2018 Farm Bill led many farmers to jump into growing hemp for CBD. This type of hemp plant is short and bushy, almost like a Christmas tree. The reason being is that CBD is found in the bud and flower, so the more the better. Conversely, hemp grown for industrial applications like textiles look much different. They are tall and reed-like, because it is the stalks that are needed for material. Hence, longer stalks with less flower is ideal.
When hemp is produced for fiber harvesting it starts when the plants are in between the early bloom stage and seed set. It is carefully conducted to make sure the stalks do not get damaged during harvesting. Once hemp is harvested, the various components of the plant stem need to be separated - especially the valuable bast or inner core, and fiber.
Historically, harvesting was done by hand by cutting the plants 2 to 3 cm from the soil using a machete, shears, or scythe and then stacking them in pile to make it easy to transport them for either retting or drying.
However, there is new, modified hemp harvesting equipment that makes it possible to harvest hemp fiber using machines. This is accomplished using a decorticator, which is a machine that separates the fiber from all of the parts of the stem. Post-processing is used to remove gum and resin from the fiber.
To make the process easier, typically the fiber is retted to separate and soften the fiber before the decortication machine is used.
This is a microbial process where the chemical bonds that hold hemp stems together are broken and allows for the separation of the inner white core hurd bast fibers. These fibers are used to make twine, rope, paper, textiles, and many other things. Hemp hurd, on the other hand, can be used in pulping, building supplies (like hempcrete), and livestock bedding. The retting process is used to make the separation of bast from hurd easier during decortication. Once the retting process is over, the straw’s typically baled before being transported to a processing plant or being stored until it's required.
There are several different types of retting, and they include enzyme, chemical, water, and field. Fibre processors tend to have different, more stringent retting requirements and have to be contacted to make sure the process meets the set standards.
There are several ways that retting can be conducted with varying quality, cost, and time outcomes.
Dew retting or field retting utilizes environmental moisture in order to soften the fiber over the course of several weeks.
Green retting utilizes a mechanical process for separating the components of the plant.
Chemical retting utilizes chemicals for accelerating the separation of the fiber.
Water retting utilizes water to soften the fiber.
The retting process that is used has a significant impact on the end uses and quality of the fiber that is produced. Then the retted fiber is dried to 10 to 15% moisture to process it further.