Using scissors, cut the air bladder free from the spinal column of the cod. Rub off the thin membrane on each side of the air bladder with a piece of paper toweling, together with any bits of blood and innards on it.
Dry the air bladder in a food dehydrator at 140°–160°F (60°–70°C) for about 12 hours. The exact time depends a little on the thickness of the air bl