When sterilizing glassware such as bottles, petri dishes and test tubes, dry heat is required and this is carried out in a hot air oven. The ideal temperature of the oven needs to reach is at least 160°C and the contents need to be regulated at this heat for 45 to 60 minutes. The contents must not be removed from the oven immediately as a slow cooling period is necessary – ideally when the temperature has reduced down to 50°c, but no less. The reason for the gradual cooling period is to avoid the cracking of glassware as well as preventing air (that could potentially contain contaminating organisms) entering the oven.
All items that require dry heat sterilizing need to be dry. For the purpose of routinely drying glassware a lower temperature of 60°C is acceptable.
Appropriate containers for use in a hot air oven are as follows:
- Glass pipettes (graduated and Pasteur) with ends plugged to a depth of 20mm with non absorbent cotton wool
- Nylon or glass syringes (polypropylene or other types of plastic are not suitable).
- Metal needles, lancets and forceps
- Dry swabs in glass tubes
- Glass or aluminum petri dishes
- Glass test tubes – aluminum tops or non-absorbent cotton wool plugged
- Bottles with aluminum tops with silicone linings
- Glass flasks or cylinders covered with aluminum foil