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Hi Techies,

I had an interesting experience when using our old pressure cooker last week.

I was sterilising bottles of deionised water for an upcoming prac.

The pressure cooker contained water, 6 x 250 ml duran bottles containing water, the blue lids loosely on the bottles.

Also contained a small strip of autolave tape and a sterility indicator strip.


2/3 of the way through the process of sterilising along with the steam coming out there was also a stench which immediately gave me a head ache and made me feel sick.

Never had this happen before.

Trying to work out the source of the stench.

Wouldn't be the glass bottle or the water.

I think it was either the autoclave tape ( a new roll from livingstone although I have had it since 2012 - does it go off?)

or one of the blue plastic lids was discoloured - but it is designed for the pressure and temperature encountered.


Has anyone had a similar experience?


I use the pressure cooker mainly for making up agar and pouring plates.

I also have a steroclave which I use for sterilising inoculated agar plates. Haven't had stench problems when using it.

The pressure cooker is quicker ,that is whyI use it for the plates, the steroclave is larger and why I use it for the contaminated plates etc.

Thanks

Just wondering if some old agar had found its way into the steam vent? I can't see it being anything that you had in there on that occasion.

And funny story - for some weird reason, every time I cooked up agar in the autoclave the smell made me hungry. After years of doing this, it only dawned on me this year that the smell reminded me of the dining room at uni. Says a lot about uni food...

The stench - what does it smell like?

It had a chemical / burning sort of smell about it.

I have since learnt that autoclave tape depending on brand has a use by date / lifespan of 5 years.

I have just autoclaved some contaminated petri dishes at 121C and some of the agar (melted and) came out of the petri dishes.
While the molten agar stayed in the autoclave bag, I thought it was meant to stay in the petri dishes.
Should I be concerned about this (i.e. is the agar likely to have become gaseous and lodged in the valves of the autoclave) or is this normal?

Thanks in advance for your help!

Hi Beaker. This is normal. When I sterilise agar plates in the pressure cooker, I don't use a bag and the plates turn into a sodden, twisted mass of plastic and melted agar, and I've never experienced issues with getting gunk through the cooker valves. (Love your name, by the way. I used to watch the Muppets too - I'm jealous I didn't use that name!)

I use an oven bag to sterilize the agar plates. they smell a bit like vegemite on a good day, and dreadful on a bad day.

I have an electric pressure cooker here. At my old school I had an old one that I used to just put on the magnetic stirrer/hotplate for a while and hope for the best... Any recommendations for settings, times etc for an electric one?

RosalieL wrote: ↑05 Dec 2022, 10:11 I have an electric pressure cooker here. At my old school I had an old one that I used to just put on the magnetic stirrer/hotplate for a while and hope for the best... Any recommendations for settings, times etc for an electric one?

If you look up Science Assist they have an AIS on sterilising agar which state that "The most effective and suitable method of sterilising agar is by using moist heat in the form of steam under pressure i.e. 121oC for 15 minutes at 15 pounds per square inch (psi). This method will denature & coagulate enzymes and other cell constituents in the bacterial cell. Sterilization can be guaranteed only when these parameters are reached."

Hope this helps!

Mel

melsid wrote: ↑07 Dec 2022, 11:48

RosalieL wrote: ↑05 Dec 2022, 10:11 I have an electric pressure cooker here. At my old school I had an old one that I used to just put on the magnetic stirrer/hotplate for a while and hope for the best... Any recommendations for settings, times etc for an electric one?

If you look up Science Assist they have an AIS on sterilising agar which state that "The most effective and suitable method of sterilising agar is by using moist heat in the form of steam under pressure i.e. 121oC for 15 minutes at 15 pounds per square inch (psi). This method will denature & coagulate enzymes and other cell constituents in the bacterial cell. Sterilization can be guaranteed only when these parameters are reached."

Hope this helps!

Mel

Oh! Thank you! I have access to Science Assist but I forget to use it!