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Does anyone out there have experience using reusable petri dishes, either glass or ppe? I have a few questions about thier use.
1. Do you pour them before or after sterilization?
2. If before, how do you keep them sterile after autoclaving? (I thought about using a FP bag, heat sealed.)
3. If after, how do you pre-sterilize the empty plates? (I thought about doing the same trick as above, leaving them in the bag until ready to use.)
My first attempt was pre-pouring, placing them in an FP bag and heat sealing, sterilizing for 20 min at 15psi, and cooling. Unfortunately they either took on water or the gel strength of the agar had died, since they were watery.
If you pour the agar medium into the petri dishes before sterilizing, you lower the potential for contamination. The only downside is that you have to pre-melt the nutrified agar solution, pour it into the dishes, and allow it to solidify before pressure cooking.
Well, that's what I did, with mixed results. I put the poured plates (20) in a FP bag, sealed it, placed it in my pc and gave it 45 min @ 15psi.
They came out fine except for two things:
1. There was lots of condensation, more than I'd like (the covers are hard to see thru and the condensation drips onto the agar.)
2. Several plates on the top of the stack fell off in the cooking, and dumped their contents, forcing me to toss them and all the ones on the bottom layer. Some way to stack them securely would be good, but I haven't figured that one out yet.
Stack the plates not more than 5 piece high, then put onto a piece of aluminium foil and fold the foil around them. Place in the PC on a rack and very little water. PC for 20 minutes(40 minutes is definitely an overkill). Let cool in the PC. You will always have condensations if you srtilize allready filled petris.
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