Can't seem to get the medium right. Help!

[Kasiopea]

Hi guys,
I made a set of jars a good while back and everything went by the book. But since then I've been trying to prepare another flask batch, three times now to no success. What seems to be happening is I can't get the proportions right and the medium does not gel correctly. First failed attempt, the medium seemed too wet and separated, the charcoal dust settling on the bottom, and if you shook the flask the media would just swoosh around as it never firmed. I though it was an old pack of media, and ordered fresh stuff. Well the same keeps happening to me over again. The media seems to not gel well and then, the next morning there is some extra liquid separation on the top. The longer it sits, it seems to get more soft, fall apart in chunks if you tilt the flask. First time I got grayish gel on top and charcoal settled on the bottom. Second time media was black throughout but had water later on top and broke appart. Third time it all completely separated into water, and media settled on bottom.
Here are my steps:
1.Add half pack of the black medium (sold in silver packets on eBay) to 500ml water. Gradually, mixing well.
2.Bring to boil for a couple minutes steering then pour into flasks.
3.Close flask and sterilize in a boiling pot of water for 30min. I add enough water to cover 3/4 of the up right standing flask at boiling and make sure the lids are above water so no water leaks in.
What am I doing wrong? I also hear that people prepare media in a microwave? how does that work? how long do you nuke it to sterilize?

[estación seca]

Agar retains its ability to set for a very long time, so old medium should not be the problem. Too-soft agar means too much water in the mixture or it was not heated and mixed enough. Possible causes might be not as much agar in the envelope as there should be; steam condensing inside the flask; the flask not getting hot enough; or, you adding too much water. It is probably not the third if you're being careful measuring.

You're using too much water in the sterilizing container. You only need enough to make sure it does not boil dry during the time you want the jars to be heated. Steam can be heated to any temperature above boiling, but water can only be heated to the boiling point. The whole point of steam sterilization is to get things hotter than boiling water, and you cannot do this if any of the jar is touching liquid water. It would be better to have a wire rack to hold your flasks out of the water completely.

Are you covering your boiling container? Have you considered using a pressure cooker instead of simply boiling? You will have much better results with pressurized steam rather than simple boiling. Pressure cookers are very inexpensive compared to the extra contaminated flasks you will have with plain boiling.

[Kasiopea]

I see what you mean, I'll try again with less water and optain a pressure cooker. I guess also it is better to just make a whole pack worth to make sure the powder in the packer it mixed uniform and I do get the right proportion. I believe it's 1liter per pack right? How long can prepared jars bee good for if I don't use them all right away, given no contamination occurred ?

[estación seca]

Unless you have a scale that can measure milligrams, you won't be able to divide packets accurately. It is hard to ensure the opened, unused packet remains sterile. I would always mix the whole packet at once.

You would have to get the water proportion from the seller.

There are sterile containers with uncontaminated liquid media on display at the Pasteur Institute that were prepared by Pasteur himself over 100 years ago. Commercially-available prepared bacteriology agar plates generally have expiration dates in the days to weeks range. I would think prepared, lidded flasks could easily be stored in a cool room for months once sterilized.

[Cntry]

Kasiopea, how did the next batch work out for you? Did it come out correctly once you used the full package work of ingredients?

[Silje]

I've never had this problem. I have no idea what the problem could be.

I have a box of powder for 10 liters and I make one liter at the time whenever I need it. I'm using P6668 medium, about 1 1/2 teaspoon per liter of water and add 1 teaspoon agar-agar. It's stiff, but not too hard for the roots. I don't sow that much so the box with powder for the growth medium stays in the fridge for a very long time, but it doesn't seem to do any damage.

I sterilize the flasks in pressure cooker. Always successful, never any contamination.