Stifling kills the pupa before the moth can emerge and cut through the shell, which would break the continuous filament and drop the cocoon to ghicha grade. Drying then removes moisture so the cocoon can be stored without rotting. How far you dry depends on how long the cocoon has to keep.
Stifling and drying schedule
| Requirement | Temperature | Duration | Driage |
|---|---|---|---|
| Stifling only | 115 – 95 °C | 2 hours | 10 % |
| Medium drying | 115 – 80 °C | 4 hours | 35 – 40 % |
| Full drying | 115 – 70 °C | 8 hours | 60 % |
Driage is the percentage weight lost during stifling and drying. All three schedules start hot and step down — the initial high temperature kills the pupa quickly, the falling temperature then drives off moisture without scorching the shell.
Muga cocoon drying chamber
The institute’s hot-air stifling and drying unit (2005) is fired with locally available firewood and dry leaves and handles 8,000 cocoons per cycle. It needs no electricity, works in all seasons and suits remote areas — and gives better silk recovery and longer storage life than either sun drying or the traditional smoke stifling it replaces.