It takes about five minutes to open the cotton. Bring a large iron pot filled with water to a boil and put the silkworm cocoons into the boiling water first. Then use a large mesh spoon or other tools to continuously stir the silkworm cocoons in the hot water, as the water rolls, until the silkworm cocoons become softer and softer. When the water in the pot turns yellow (silkworm chrysalis soup), you can scoop it up and put it in a clean hot water basin next to it.