How to Autoclave a Liquid

The autoclave procedure is somewhat difficult.

An autoclave machine uses pressurized steam to sterilize. The heat and steam in the autoclave force air out of the autoclave chamber and destroy microorganisms in liquid. Besides sterilization, an autoclave is used to decontaminate dangerous liquid waste before it is thrown away. In order to sterilize the liquid properly, the autoclave needs to be used properly. Using the wrong containers and heat and pressure programs can damage the autoclave.

Things You'll Need

• Polypropylene jars or tubes or laboratory-grade glassware containers with lids
• Aluminum foil
• Autoclave tape
• Stainless steel or polypropylene pans, at least 5 inches deep
• Autoclave instructions
• Heat-insulated gloves

Instructions

1. Fill liquid containers half full with the liquid. Appropriate containers include polypropylene jars or tubes or laboratory-grade glassware; they can withstand the temperatures and pressure of the autoclave process without breaking. Place each container's lid on the container loosely. If the lid is a screw cap, then tighten the cap only half way. In place of a cap, you cover a container's opening with aluminum foil. Tape a piece of autoclave tape to each container. At the end of the autoclave process, the tape will reveal whether or not the autoclave machine reached the proper temperature.

2. Place the covered liquid containers in a secondary container, such as a stainless steel or polypropylene pan, that is at least 5 inches deep. You may place more than one container in a pan. The secondary container catches material that boils out of liquid containers that were filled too high. It also prevents containers or other items from falling to the bottom of the autoclave and making a mess.

3. Arrange the liquid containers in the pan so that space is between the containers. The space is necessary, allowing steam to circulate around each item.

4. Select the liquid cycle on the autoclave. The liquid cycle uses a slow exhaust, which helps to prevent liquid from boiling out of the containers. Set the time for the liquid cycle. Liquid containers that are large take longer to autoclave than containers that are small. For example, 1L of liquid in a 2L bottle requires longer time in an autoclave than 250mL of liquid in four 500mL flasks. Check the autoclave instructions for the appropriate autoclave time.

5. Place the pans holding the containers in the autoclave. Close the autoclave door, rotating its handle clockwise until the door seals tightly. If the door does not seal correctly, then steam will leak, and the autoclave will not reach the necessary temperature or pressure.

6. Start the autoclave, and allow the cycle to finish. Before opening the autoclave chamber, verify that the autoclave pressure is zero.

7. Remove the pans from the autoclave with heat-insulated gloves. The containers still may be hot. Allow the liquid to cool completely before use.

References

• University of Maryland, Environmental Safety: Autoclaving Procedures
• University of Guelph: Autoclave Standard Operating Procedures; 2002
• "Qiagen News"; The Qiagen Guide to Good Microbiological Practice; Issue 4; 1998