what is retting

Retting is a process that involves the use of microorganisms and moisture on plants to dissolve or rot away much of the cellular tissues and pectins surrounding bast-fiber bundles, facilitating the separation of the fiber from the stem. The process is used to separate the fibers from the plant stem, and it is commonly used for plants such as flax, hemp, and jute. The most widely practiced method of retting is water retting, which involves submerging bundles of stalks in water. The water penetrates to the central stalk portion, swells the inner cells, and bursts the outermost layer, thus increasing absorption of both moisture and decay-producing bacteria. Retting time must be carefully judged; under-retting makes separation difficult, and over-retting weakens the fiber. In double retting, a gentle process producing excellent fiber, the stalks are removed from the water before retting is completed, dried for several months, then retted again. Natural water retting employs stagnant or slow-moving waters, such as ponds, bogs, and slow streams and rivers. The stalk bundles are weighted down, usually with stones or wood, for about 8 to 14 days, depending upon water temperature and mineral content.