JEDilworth bactitech at nospamhortonsbay.com
Wed May 1 23:02:59 EST 2002

I think I read somewhere that the most important safety thing you must
watch out for with pressure cookers is to keep the vent from getting
plugged. The steam MUST have an outlet or it will explode. Agar could
very well solidify and plug the vent. You must make sure you have enough
head space. I wouldn't worry so much about damaging the agar as damaging
YOU. We always boiled the agar over a hot plate or bunsen first, made
sure the agar was dissolved (it must boil for a minute to dissolve agar
agar). Then we put gauze over the top of the flask, taped with autoclave
tape (the stripes turned black whe proper temperature was applied) and
then autoclaved.


gives a lot of good information about pressure canning, and checking the
gauge. etc. 

I've cooked with pressure cookers before. Steam canners are much bigger
and probably more what you're looking for. It's very important that you
follow directions exactly for these appliances. 

Low acid foods must be steam processed under pressure to kill spores of
C. botulinum, whereas acid foods can be processed by boiling. The only
way you can adequately kill spores is to apply pressure so the
temperature can be raised above the boiling point. It would be well to
purchase some steam autoclave controls of some sort to run with your
batch to make sure you have attained the correct temperature.

I believe we used to process our media at 15 lbs. pressure for 15
minutes in the autoclave. You must slowly exhaust the steam or your agar
will boil over and explode, possibly plug the vent and/or burn you. By
the time you add the time to get the pressure up and cool it down it
takes much longer. You can only run instruments or things without liquid
on a fast exhaust cycle in an official autoclave. I would suspect a
steam pressure canner would be similar.

I would think reusing microscope slides would be a pain. You'd have to
clean them off, they stick together, and would generally be much more
trouble than they're worth. I would buy a few boxes and be done with it. 

Can't you buy your media commercially prepared? Perhaps you can make a
deal with a nearby lab, where you could use their autoclave for one
evening a month to make stuff.  

Judy Dilworth, M.T. (ASCP)

Des O'Connor wrote:
> Hi Shaun
> I suspect the device you require is not manufactured. The use of a culinary
> pressure cookers is unwise for the intented purpose as it may prove
> unreliable,damage the agar and may be unsafe.

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