Agar plates are petri dishes prefilled with agar solution. Some plates come empty and are filled by the user. The agar solution serves as the base for growing certain types of bacteria and organisms which cannot grow in "suspension," that is grow in simply liquid media. The agar allows the growths to attach and spread across the surface. To minimise the risk of contamination; most lab equipment is sterilised in a high heat and high pressure chamber known as an autoclave.
Place the agar plates evenly spaced apart inside an approved autoclave tray. Most labs have these large bin-like trays next to the autoclave. Do not use any other holding container in the autoclave.
Loosen the lids of the plates if they are the kind with tightening lids. Otherwise leave the lid fully in place. Place any other items to be autoclaved with the plates in the tray next to the plates. Do not stack the plates or other items.
Make sure that the bottom of the autoclave chamber is filled to the proper fill line with distilled water. Verify that the settings on the autoclave have not been altered from the standard setting of around 121 degrees C (121 degrees C) with pressure between 15 and 19 psi.
Slide the loaded tray into the autoclave, close the chamber door and engage the door lock. Verify the door is locked and press the "power" button on the autoclave. Set the timer to the desired amount of time. For just agar plates, the time is anywhere between 15 and 30 minutes, depending on how full the autoclave tray is.
Wait for the timer to go off and the pressure gauge on the autoclave to reach zero before opening the chamber door. Stand back and wait until the tray is cool before removing the items. Do not open the agar plate lids and tighten any loose lids.
Prepare your desired cell media before autoclaving the agar plates. Pour the media into an autoclave safe vessel with a twist cap and autoclave the media along with the plates. If you are using empty agar plates, autoclave the agar solution in a separate vessel alongside the plates and allow it to cool before pouring it into the plates. The agar in prefilled plates may soften after autoclaving; use care when moving the plates until the agar hardens again.
Do not open the chamber door during the autoclave process or when the pressure gauge is above zero. The hot steam inside the autoclave is highly pressurised and can blast the door right off the autoclave causing injury and damage. Do not handle the tray or items without the use of lab-approved heat gloves and wear eye protection when opening the autoclave. Do not use regular plastic petri dishes in the autoclave, as these can melt.