Microwave Autoclave

[adomant]

I'm just getting into yeast cultures and the issue of sterilisation - conventional wisdom is that a pressure cooker is a good idea but I also wanted to explore the microwave option.

Various searched have shown that the biochemistry industry is, at best, uncertain that microwaves will kill spores and at worset, largely sceptical. However, that is just looking at microwaves on there own as a source of dry heat.

I read an article on using microwaves in combination with steam (like baby bottle setirisers) which suggest that the appropriate kill factor can be reached ( 6Log10 ?).

one of the sources http://www.elaw.org/system/files/Non-Incineration_Medical_Waste_Treatment_Te_7.pdf

So I have bought one of those cookware microwave pressure cookers and I'm going try to sterilise a plate on full power for 20 minutes with steam and see if anything grows or maybe use a colour indicator.

I will buy a pressure cooker as I have no doubt that this is too convenient to work.


thoughts appreciated...

 

[Vossy1]

As the purpose of your post is to 'experiment' a, I will be interested to hear your results.
Without seeing to be negative, how will you be able to differentiate between kill rates accountable to steam v microwave.

So I have bought one of those cookware microwave pressure cookers and I'm going try to sterilise a plate on full power for 20 minutes with steam and see if anything grows or maybe use a colour indicator.

How will you ensure no cross contamination, how will you ensure back ground environment will be excluded from your experiment?

 

[31bb3]

Where are you planning on keeping the plate once steralised it needs to be sealed somewhere otherwise its going to be open to airborn bacteria which will ruin your experiment

 

[adomant]

The experiment will need to reasonably within the capabilities available to me (I am not a biochemist and I will be using a kitchen instead of a lab).

Hyothesis is that a Microwave using steam under some pressure can sterilise as effectively as autoclaving in a pressure coooker.

The method will be to prepare 3 agar plates and sterlise one in a pressure cooker for 20 minutes, 1 in a microwave pressure cooker for 20 minutes and the 3rd for 40 minutes (both at full power).

the plates will be sealed with parafilm or nylon tape and incubated in a sanitised box at 25-30C for 10 days.

The dishes will be inspected for any signs of growth using a magnifying glass.

I will explore the option of using an indicator as well.

hopefully I will get time to start this on the weekend...

 

[31bb3]

Should be interesting to find out what happens

 

[adomant]

Epic failure, experiment abandoned

conclusion - don't attempt this, if I have saved others a bollocking from the missus then hopefully it has been some use.

The microwave "pressure" cooker cannot maintain a pressure anywhere near enough to stop fluids boiling over.

After 20 minutes, there was a "cosmic soup" in the cooker, plates and slants.

I salvaged one slant that had wort / agar in it and I will see what develops in that. Will stick with hob pressure cooker from now on.

 

[Hoppyland]

For whatever use it may be to brewers:
http://www.iosrjournals.org/iosr-jdms/papers/Vol12-issue3/A01230105.pdf

I've also recently read that 3 mins in a domestic microwave on full will kill pretty near all food spoilage organisms - definitely all that might cause beer spoilage. Having a little moisture in there helps. I now do this with all of my yeast-slope and yeast starter kit.