rot-steep
To steep (cotton) to remove impurities.
rot-steep: soaking cotton to break down plant matter
Rot-steeping is the process of soaking raw cotton fibre in water, sometimes with added alkali or mild acid, to soften and partially decompose the waxy, gummy, and pectic substances that bind cotton fibres together and cling to seed fragments and leaf matter. The cotton is submerged in large vats or tanks, and the biological and chemical action loosens these impurities so they can be washed away in subsequent processing.
The term rot refers to the controlled microbial and enzymatic breakdown that occurs during steeping, not to decay or damage. Temperatures typically range from 50 to 80 degrees Celsius, and steeping times vary from 12 to 48 hours depending on the grade of cotton and the desired degree of softening. The water may be acidified with dilute sulphuric acid or treated with weak alkali solutions such as sodium carbonate to accelerate hydrolysis of the binding substances.
Rot-steeping occupies an intermediate position in cotton preparation, coming after ginning (which removes seeds) and before scouring and bleaching. It works most effectively on upland and pima cottons that carry significant amounts of natural wax and plant debris. The process is less critical for already-clean cotton but still improves the speed and uniformity of subsequent wet processing and dye uptake.
Common faults include incomplete softening, which leaves knots and hard specks in the fibre, or over-steeping, which can weaken fibre strength. The spent steeping liquor contains dissolved lignins, pectins, and other organic matter; in older mills this was discharged directly, but environmental regulations now require treatment or recycling of these waters before release.
Rot-steeping is distinct from hot-water scouring and from fermentation methods used in some linen and hemp processing. Modern cotton mills may combine or skip rot-steeping in favour of faster alkaline scouring, but the technique remains valuable where cotton fibre quality is uncertain or where very clean, soft fibre is required for fine counts and delicate fabrics.