The initial smoking (often using sawdust, which can produce more smoke at a lower temperature than intact wood) takes place at a relatively cool temperature around 85°F/30°C, which avoids hardening the surface and forming a barrier to moisture movement from the interior. This also allows the fish flesh to lose some moisture and become denser without being cooked, which would denature connective-tissue collagen and cause the fish to fall apart. Finally, the fish is smoked for several hours in one of two temperature ranges. In cold smoking, the temperature remains below 90°F/32°C, and the fish retains its delicate raw texture. In hot smoking, the fish is essentially cooked in air at temperatures that gradually rise and approach the boiling point; it reaches an internal temperature of 150–170°F/65–75°C fairly quickly, and has a cohesive yet dry, flaky texture. Fish smoked cold and long can keep for as long as a couple of months in the refrigerator, while a light smoking, hot or cold, will only keep the fish for a few days or weeks.