Help with autoclave & agar/wort loss...

[Jimbo]

Hey there,
I just tried to make my very first set of plates & slants. I used my pressure cooker as an autoclave... Here's what I did:

All the stuff is "autoclave safe"
4 - Petri dishes (about 15ml of agar/wort solution)
4 - 16x125mm Culture Tubes (about 10ml of agar/wort solution)
4 - 16x125mm Culture Tubes (about 10ml of wort)

I put the Culture Tube caps on the tubes "loosely". Put the Petri dishes and culture tubes in the pressure cooker. Heated them (steamed) for 30 minutes.

Here my question:
Was I supposed to tighten the caps on the Culture Tubes? I was nervous that the Culture Tubes might explode if I tightened them...

About half the agar/wort mix boiled away from all the tubes...

Thoughts?

Update:
I was wondering if the agar/wort solution would boil when it was in the pressure cooker - I learned that, YES, agar/wort solution does indeed boil inside the pressure cooker! Since that is the case, my next question was the one list above - as a means to reduce the agar/wort loss, is it ok to close the lid on the tubes to prevent loss...

[Mylo]

Hmm, I don't have a pressure cooker, but I would have thought that the pressure inside the unit keeps things from boiling over. Did you open the lid before everything was cool?


Mylo

[Jimbo]

Well, I did let everything cool off (but it was still kinda hot when I opened it - I wanted to make sure to "lean" the slants before the agar/wort solution solidified), however, there was clearly some wort left in the water in the bottom of the pressure cooker. Also, there was anywhere from 3 - 5ml in each of the tubes instead of the 10ml originally... The only place it could have gone is into the air/steam...

Also, the petri dishes/plates also had significantly less agar/wort solution left after the boil than before.

[DannyW]

If you manually released any pressure from the cooker or sprayed the outside of the kettle with water to cool it off faster then you will get uncontrolled boilovers inside and half your wort, agar, soup, whatever will end up in the bottom of the kettle.

I have to let mine sit undisturbed until I see the pressure latch let go all by itself or I get the same results as you. The pressure latch in my kettle is a little bit of metal between the handles of mine. It retracts all by itself when the pressure is the same inside and out.

[Jimbo]

You nailed it...

I cooled it off to open it by running it under water (per the pressure cooker directions for COOKING not autoclaving!) I'll try again and this time be patient...

Any opinions on keeping the caps loose or tight?

[DannyW]

I'd only snug them down if you are trying to draw a vacuum. I don't know if that is proper procedure with tubes like it is for canning jars.