The most widely practiced method of retting is called
water retting, by submerging bundles of stalks in water. The water, penetrating to the central stalk portion, swells the inner cells, bursting 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 fibre. In double retting, a gentle process producing excellent fibre, the stalks are removed from the water before retting is completed, dried for several months, then retted again.
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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.
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Tank retting, by contrast, employs vats usually made of concrete, requires about four to six days, and is feasible in any season. In the first six to eight hours, called the leaching period, much of the dirt and colouring matter is removed by the water, which is usually changed to assure clean fibre. Waste retting water,
which requires treatment to reduce harmful toxic elements before its release, is rich in chemicals and can be used as liquid fertilizer.
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