Hemp Retting and Decortication

Hemp retting and decortication are the two primary fibre extraction stages converting harvested hemp stems into processable bast fibre. Retting degrades the pectin middle lamella (calcium and magnesium pectate) binding fibre bundles to woody core using microbial (dew retting 3–6 weeks, water retting 7–14 days), enzymatic (pectinase-xylanase cocktail, 40–55°C, 8–24h), or chemical (NaOH 0.5–2%, 80–100°C) mechanisms. Degree of retting is assessed by fibre bundle separation ease, shive content, and strength retention. Decortication mechanically separates retted bast fibre from hurds (woody core, 65–70% of stem dry weight) using breaking rollers, scutching paddles, and hackling combs, achieving line fibre (Nm 5–15) and tow (Nm 1–4) fractions. Combined retting-decortication processing adds €0.40–0.80/kg to fibre production cost versus raw straw at €50–80/tonne. Hurds valorisation at €80–150/tonne as animal bedding, hempcrete aggregate, or particleboard filler recovers 40–60% of processing cost.