Australia's Science Forum

Our Biology teacher is having trouble viewing the agar plates as the condensation stops the view of the growing bacteria etc. Does anyone else have this problem? They are only incubated at 30 deg and looked clear till they sat out for two hours before viewing and had then condensed up again. Any ideas please?

Do you incubate and store them upside down? I have had this problem before from storing the plates in the fridge before the class uses tham. storing upside down seems to help.

I put them upside down, but I also put the sticky tape around the lid in 4 separate strips with about 3cm gap between them.
Lada

I was always taught that they should be stored , incubated upside down - so the set agar is on the top there fore any condensation is on the bottom - but then when you go to look at the growths they will turn them up and the water will go to the plate.

I was told that an over amount of condensation was from pouring the agar too hot.

I know that my method has huge risks of contamination and would never be used in a microbiology lab, but it works for us.
I pour the agar when it is cool enough to handle the bottle and then I LEAVE THE LID OFF THE PETRI DISH until it has cooled completely.
I then store and incubate upside down and I never have condensation problems.
Microbiologists would be shaking their heads in dissaproval but we only get growth of bugs where the students smear their cotton buds across. I incubate at 30 degrees.

Thanks for you replies. I have making these plates for ever and had never had a problem. Yes, I store and incubate at 30 deg upside down. I was thinking that taking them out of the incubator two hours before looking at them may have caused the problem but apparently they fogged up within five minutes. The senior class is doing it as an assessment next week, so we might try Lada's sticky tape method - not sticking all the way around. I have thought of parafilm but I don't have any and don't know if the same problem would occur.
Thanks again for your input