Silkworm
larvae are fed with
mulberry leaves, and, after the fourth
moult, climb a twig placed near them and spin their silken
cocoons. This process is achieved by the worm through a dense fluid secreted from its structural glands, resulting in the fiber of the cocoon. The silk is a continuous filament comprising
fibroin protein, secreted from two
salivary glands in the head of each larva, and a gum called
sericin, which cements the filaments. The sericin is removed by placing the cocoons in hot water, which frees the silk filaments and readies them for reeling. This is known as the degumming process. The immersion in hot water also kills the silkworm pupae.
Single filaments are combined to form
thread, which is drawn under tension through several guides and wound onto reels. The threads may be plied to form
yarn. After drying, the raw silk is packed according to quality.