A commonly used method for heat sterilization is an autoclave, sometimes called a converter or steam sterilizer. Autoclaves use steam heated to 121–134 ° C (250-273 ° F) under pressure. To achieve sterilization, the product is placed in a room and heated with injected steam until the product reaches a temperature and time set point.
Almost all the air is removed from the room because air is not desired in the moist heat sterilization process (this is a characteristic that differs from a typical pressure cooker used for cooking). The product is kept at the temperature set point for a varying time depending on what biological load is present on the sterilized product and its resistance to steam sterilization (D-value).
A common cycle will be anywhere from 3 to 15 minutes at 121 ° C (depending on heat generated) at 100 kPa (15 psi). After sterilization, liquids in a pressure autoclave should be cooled slowly to prevent boiling when the pressure is released. This can be accomplished by gradually depressurizing the sterilization chamber and allowing the liquids to evaporate under a negative pressure while the contents are cooled.