Preparation of agar medium for flasking

[Afid]

I am getting ready to flask some seed but I am a little confused by the instructions for preparing the media. http://orchidseed.com/OSPmediapreparation.pdf I think that I am supposed to pour the cold agar-water mix into the flasks, then place them in a pressure-cooker with some water. is this correct?

[Afid]

It also says on the package that a PH adjustment may be necessary, how do I do that?

[Afid]

Also, am I correct in thinking that the lid should be on the flask when it is in the pressure cooker?

[Afid]

Bump

[Afid]

I have now mixed the medium and poured into flasks, but I have about 500ml of extra medium left over, is it possible to store it for later use?

[neophyte]

I am pretty sure it's possible to store the extra medium as long as you chill it. I'm not sure whether a refrigerator or freezer would work better. I doubt the agar will just degrade so it's definitely storable, but the additives (especially plant hormones) may break down over time, and lowering the temperature would simply delay that process (and obviously slow down microbial growth). If you end up using it again you would probably want to re-sterilize it though.

[Afid]

Sounds good, thanks!

[neophyte]

by the way, did you leave the lids on or off?

[Afid]

I left them off, which seemed to work (although some water did get into two flasks because they tipped). Having said that, it has been nearly 6 hours since I did the first 4 flasks and they have not set yet, should they have or does it take awhile?

[neophyte]

Do you mean the medium has not gelled? It usually takes around 45 min for agar to solidify. I would say an hour at most under room temperature. Maybe the medium contains too much water? I have no idea how a pressure cooker works. Does it involve steam? Maybe the steam diluted the medium...?

ps: assuming you are using a medium that contains plant supplements, how would you know that these additives are not destroyed by the pressure cooker? just wondering.