retting and hemp fiber extraction

Industrial hemp has been used by human beings for thousands of years. Many of the methods we use to manufacture hemp textiles today have been handed down through generations. Of these, retting is a critical step in the hemp fiber extraction process that works to separate important plant materials.

The practice of retting finds its roots in hemp fiber extraction and in other naturally occurring materials like flax. Whether it be with hemp or flax, retting is critical in transforming natural materials into textiles like clothing, furnishing, and bedding.

To better clarify this important step in industrial hemp processing, we put together this brief exploration into the hemp retting process.

What is Retting?

As seen with other ingenious manufacturing techniques, retting utilizes natural processes to accomplish laborious tasks. The retting process takes place after the stalks of hemp plants have been harvested and are ready to be turned into textiles. The goal of retting hemp is to prep stalks for the separation of valuable fibers from other plant materials.

The retting process utilizes water and bacteria to decay tissues that surround bast fiber in hemp stalks. By putting stalks in the right environmental conditions, hemp farmers literally let them rot to initiate the fiber separation process. The USDA puts it this way, “Retting is a microbial process that breaks the chemical bonds that hold the stem together and allows separation of the bast fibers from the woody core.”

The process of retting is used by people around the world to help transform natural materials like flax, hemp, kenaf, jute, and ramie into usable textiles.
Studies show that a number of different bacteria work to break down plant materials when retting hemp, these include “Bacillus mycoides, B. subtilis, Erwinia carotovora” and many more.

Different Types of Retting Processes

In experimenting with the retting process, people have devised multiple ways to separate plant materials using bacteria and moisture. Today, the most popular forms of retting are field retting (also known as dew retting) and water retting.

Field Retting

In the practice of field retting, harvested hemp stalks are left outside on the ground for weeks after they are harvested. By simply cutting down hemp plants and leaving them in the field, farmers allow water and bacteria to work together to decay the stems. Depending on weather conditions, the field retting process often takes 2-3 weeks.

Field retting works most effectively in humid locations with high dewpoints. These regions of the globe harbor the right environmental conditions for rapid bacteria growth.

Water Retting

With water retting, farmers soak the stems of hemp plants directly in water to initiate the breakdown of plant materials surrounding valuable fibers. Water retting takes place in holding tanks or ponds where producers can carefully monitor bacteria activity, as well as the overall state of the hemp fibers.

Water retting is a great option in parts of the world where environmental conditions are not favorable for field retting, such as deserts and dry climates.

Retting Hemp

As the hemp industry continues to take shape, producers are working hard to figure out which manufacturing processes are profitable. Importantly, hemp farmers must not only choose a hemp retting process that makes sense in their location, but they must also fit it into their budgets.

While both field retting and water retting are viable options for fiber extraction, field retting is the most commonly used practice for retting hemp. Water retting produces higher quality fibers than field retting. However, as water retting requires extensive infrastructure, water, and labor, it is too costly to make sense for most hemp farmers. In the end, the value of hemp fibers made from water retting doesn’t outweigh the costs of producing it.

Hemp growers must harvest and manufacture their products in a very specific order. To this end, retting hemp takes place after plants are harvested with commercial hemp farming equipment like combines.

Hemp Fiber Processing

The hemp fiber extraction process occurs along a carefully choreographed chain of events. Each of these steps must occur in the correct order to meet the demands of the industrial hemp supply chain.

Please note, the stems of industrial hemp plants produce two types of useful materials: bast and hurd. Throughout history, industrial hemp plants have been grown almost exclusively for bast production. Hemp bast produces the long, string-like fibers for which industrial hemp is known. Conversely, hurd is the wood pulp-like substance in the inner stem of the hemp plant.

The hemp fiber extraction process was developed to isolate bast from the rest of the hemp plant material. While hurd was once considered a waste byproduct, today it is being utilized for such products as insulation. As will be seen below, hurd is removed during the scutching step of the extraction process.
The steps of the hemp fiber extraction process are as such:

  • Cultivation: industrial hemp plants are grown specifically for fiber production.
  • Harvest: plants are cut after the flowering period when fibers are the strongest.
  • Retting: water and bacteria break down plant materials.
  • Breaking: hemp stems are broken down further with a “hemp breaking machine.”
  • Scutching: stems are smashed to separate valuable hemp bast fibers from less desirable hemp hurd materials. The hemp hurd materials are removed for other products.
  • Hackling: hemp bast fibers are further cleaned using a comb-like tool.

When hemp stalks are finally finished being processed they are ready to enter the next phase of the supply chain. At this point in the process, fibers are sold to textile manufacturers who make countless products from clothing to building materials.

Contact High Grade Hemp Seed with Questions

At High Grade Hemp Seed, we are proud to produce some of the finest CBD genetics in the world and take great pride in educating our customers about industrial hemp.

Please contact us to learn more about how to process hemp or how to separate hemp fibers.