In order to sterilize a given set of materials, the appropriate conditions of heat and moisture must
be used. Moist heat coagulates microbial proteins (including protein enzymes), inactivating them
irreversibly. In the dry state, protein structures are more stable; therefore, the temperature of dry
heat must be raised much higher and maintained longer than that of moist heat. For example, in a
dry oven, 1 to 2 hours at 160 to 170°C is required for sterilization; however, with steam under
pressure (the autoclave), only 15 minutes at 121°C may be needed. The choice of
heat sterilization methods then depends on the heat sensitivity of materials to be sterilized.