Degumming
Also searched as: boiling off, silk degumming, sericin removal, scouring silk, ramie degumming, in the gum
Degumming removes gummy non-fiber material from a fiber: most often the sericin coating of silk, and also the pectins and hemicelluloses that bind ramie and other bast fibers.
In detail
Raw silk consists of paired fibroin filaments glued together and coated by sericin, a water-soluble, largely amorphous protein. Degumming dissolves that sericin, usually in hot or boiling aqueous baths with soap and sodium carbonate, or with enzymes, leaving the smooth fibroin that gives silk its luster, hand and drape. It can be done on yarn, or on fabric woven 'in the gum'. For ramie, decorticated ribbons are boiled in alkaline solutions to strip plant gums and separate the fibers, a step with the same purpose but different chemistry.
The science and numbers
Studies using sodium carbonate report degumming losses of about 25 to 26 percent of raw silk mass, and borate buffers about 27 percent, consistent with sericin forming roughly a quarter of cocoon silk. A common laboratory protocol boils silk in 0.02 M sodium carbonate for 30 to 60 minutes and then rinses repeatedly, and is widely used to prepare fibroin for biomaterials. Alkaline treatment also hydrolyzes and shortens fibroin chains, so gentler routes are studied: the protease papain preserves higher fibroin molecular weight, and high-temperature, high-pressure water can separate sericin without added chemicals. The moth's own protease, cocoonase, which softens the cocoon at emergence, has also been studied for degumming.
A practical example
A weaver buys raw silk yarn that feels stiff and slightly harsh. After a sample skein is simmered in a soap and soda bath, it loses about a quarter of its weight and becomes softer, brighter and more supple. Because the loss is mostly sericin, a buyer comparing prices needs to know whether a silk's weight is quoted before or after degumming.
What to distinguish
Partial degumming can be intentional, leaving some sericin for body, as in souple silks. Over-degumming, prolonged boiling or strong alkali damages fibroin, lowering strength and encouraging fibrillation. Degumming loss is different from weight added later by dyeing or by weighting with metal salts. For bast fibers the word refers to removing plant polysaccharides, not protein.
Origins and history
The English term reflects the long-standing description of sericin as silk 'gum', although chemically it is a protein rather than a plant gum. The word was later applied to bast fiber processing, where true plant gums (pectins and hemicelluloses) are removed. Hot-water and soap treatments of silk long predate modern chemistry, while enzyme and high-pressure methods are recent research directions aimed at gentler, lower-chemical processing.
Related terms
Sources & further reading
- Journal of Genetic Engineering and Biotechnology (ScienceDirect): Study on cocoonase, sericin, and degumming of silk cocoon
- Materials (PMC): High molecular weight silk fibroin prepared by papain degumming
- PMC: One-step preparation of silk fibroin and sericin from silkworm cocoons using high-temperature high-pressure treatment
- USPTO: Patent 4568739, Method for degumming decorticated plant bast fiber
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.