Most labs will need to sterilise liquid solutions. Media, agar, saline, water and lysogeny broth to name a few, but how should you do this in an autoclave?
An Autoclave liquid cycle is used to avoid the phenomenon known as “boil-over”. This is when a liquid boils so violently it spills over the top of the container. This can occur if the pressure in your autoclave chamber is released too quickly. The exhaust phase of the cycle must therefore release pressure slowly to allow the liquid to cool off as the pressure decreases.
More efficient sterilising
You can use load sensed timing whereby a flexible sensor probe is fitted and submerged directly into the media or reference bottle so that the cycle is controlled directly by the temperature of the actual load, not just the chamber temperature. This ensures the sterilisation does not begin until the very centre of the load has reached the correct temperature.
All Astell autoclaves can sterilise fluids but to sterilise fluids quickly the addition of a cooling system and air ballast must be used. After autoclave sterilisation the chamber must cool down to a safe temperature before it can be opened. If you want to speed this process up you must be careful, using a rapid cooling system would cause a sudden change in pressure and likely cause the liquid to boil over, spoiling samples and spoiling the autoclave chamber.
There are two solutions use to overcome the problem of boil over. Option one: use assisted cooling such as an external fan, water cooling (coils) or jacket cooling. These would activate at just above 100 degrees Celsius to stop a rapid drop in chamber pressure. This is the more affordable option but does leave a delay between sterilisation completion and start of the cooling process in order to prevent boil over.
Option two: use an air ballast; compressed air is quickly injected into the chamber to replace the steam used during condensation and maintain the chamber pressure during the cooling phase. With pressure maintained this process can begin immediately following sterilisation. This can be combined with internal cooling for fast and and efficient way of cooling loads.
If you have a lid for your flask place it on top and screw a half turn, make sure these are not secured as your flask will explode when the air expands as the temperature rises. If you have no lid cover your flask lightly with foil.
Add water to the level indicator line, the water must be conductive i.e. have an ionic content therefore deionised or distilled water is not acceptable. Place your flasks into the basket and place inside the autoclave. If you are using an autoclave with load sense timing place load the sensing probe into your container. Close the lid and turn the handle to create an air tight seal. Use the control panel to set the desired cycle. The Astell autoclaves have a ‘Fluids Cycle’ suitable for processing media or other fluids in unsealed containers.
Once the cycle is ends the display will show ‘complete’, the door will unlock and you can rotate the handle to open the door. Please be aware that the glassware will still be hot and you will need to use heat resistant gloves to pick up your load.
For more information about sterilising liquids using autoclaves please do get in touch with one of our technical team. You can call us on 01954 233 120, email firstname.lastname@example.org or fill in the below contact form.