Suzhou Silk Factory 2: The Cocoon Cooker
But before the cocoons are processed further they have to be stifled. In this factory they were cooked. There is a watcher for this too. Great tin baths full of intact single cocoons
are tipped into trays at the top
and these trays are sprayed then dipped with boiling water on a slowly moving conveyor so that the glue, 'fibroin', holding the silk strands together is dissolved and the cocoons start to soften and unravel.
It is the most energy-hungry part of the process and some silk mills in Hanzhou run this process using the sun.
That is the official reason for the cocoon-cooking process, but there is also another one. As the cocoons are cooked the pupa inside the cocoon is killed. The metamorphosis stops and there is no danger of the silkmoth inconveniently emerging and destroying the continuity of the thread. A broken thread has to be spun. It is not as lustrous as reeled silk and not as valuable, and I suppose makes silk unwearable by vegetarians.