Understanding the Processes for Post-Harvest Conditioning in Industrial Hemp

From textiles to hempcrete and gasoline, producers must convert hemp from plant mass to individual materials before the crop is ready to be used for industrial purposes. The process of industrial hemp processing and conditioning has been reborn since prohibition halted hemp's progress in the 1940s, and today it stands to be one of the more promising ways farmers can profit off their hemp.

How Does Hemp Go from Stalk to Wood Substitute?

Returning to its root as an industrial powerhouse in America, Kentucky farmers have grown hemp as a wood substitute since 2014. The first step after harvest is to decortify the stalks. Some producers decortify by hand using colonial-era tools, but most use industrial equipment to break the stalks into usable fibers. Essentially, this process is smashing the hemp. The short fibers should be separated from the long fibers, as the short fibers are ideal for alternative options such as paper production.

Producers then glue the fibers together and dry them out. After that, the machine compresses the hemp to a fine point of rigidity. Engineers also turn the sawdust produced from this process into bioplastic. Once compressed and stained, the hemp wood substitute is ready to use. Carpenters use the wood-alternative for flooring, interior walls, furniture, and more. HempWood®, a manufacturer in Kentucky, believes that hemp wood substitutes would work for structural and exterior builds, but their focus is on the interior.

Why Isn't HempCrete a Wood Substitute?

While it may seem like a composite wood substitute and a material made of hemp and lime are similar, there are substantial differences. First off, while hemp wood substitutes might use bast and hurd fibers glued together with wood glue, hempcrete is ideally made of hurd and lime. The hurd, or short fibers, are smaller and processed to be more consistent and thus are a better binding agent for cob techniques.

While hempcrete is a fun name, it is essentially a modified cob. Hempcrete uses plant fiber with earthen materials, resulting in a building material more similar in consistency to rammed earth reinforced with plant fiber than traditional concrete. Rammed earth is clay mixed with gravel and concrete, while cob is any mix of such materials reinforced by fibers.

What Does Industrial Scale Decortication Look Like?

The recipe for most hempcrete comes down to lime, hurd, and water. After decortication, cultivators separate the fibers either through industrial equipment or by hand. Industrial machinery streamlines this process through ducts that suck excess materials, such as rocks from the mix.

The fiber is separated from any other material through several stages of decortication and transport through ducts. Producers commonly use metal detectors to ensure no metal pieces are present in the fiber material. Once decortified, the bast goes through several cleaning cycles to separate it from the hurd. In the end, the bast is baled and ready to ship off for industrial use. Producers bale hurd separately. Some facilities capable of production at this scale require four people or fewer to operate the entire process.

What About Retting and Chemical Processing?

Retting or rotting away the hard materials of hemp can be a crucial step in conditioning hemp for industrial purposes. Yet, modern industrial tools mean that producers may skip this step. Skipping this step allows producers to save a sizable amount of money that would otherwise go to labor costs. 

For materials such as clothing, manufacturers dye the bast material after decortication. Here the hemp is chemically processed and sealed to complete the dying process. Once dyed, the bast goes through a roller, which presses the material from both sides into uniform sheets. After that, the bast is dried and put into an opener. At the end of this process, the manufacturer has usable textile fiber. Otherwise, some manufacturers spin the fine long fiber material, making rope.

While processing industrial hemp requires a demanding amount of work, machinery handles the bulk of the burden in the modern cannabis industry. Paying for the equivalent labor by human hands wouldn't be worth it except for smaller operations. Instead, hemp processing facilities in Colorado and Canada are popular choices for farmers to ship their crops to for conditioning. There are also mobile options that farms can lease.

It's Only Hemp Science, Not Rocket Science, Yet

While hemp is an alternative to plastic and metal, its simplicity gives the crop its inspiring potential. Perhaps one-day hemp will be the material used in rocket ships and trains, but as the US government stated in "Hemp for Victory," the plant was old when the temples of ancient Greece were new. Since time immemorial, pre-industrial societies have processed this plant into textiles and even used it as medicine. Now, with the benefit of several industrial revolutions, processing hemp has been streamlined and, in many cases, automated. While it's romantic to do it by hand, the future of hemp conditioning will rely on centralized processing centers that empower smaller farmers to profit from every part of their harvest.