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microwave for sterilization

sleepy

sleepy

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Joined
Dec 4, 2007
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i saw on a talk show or something once that you could sterilize your nasty kitchen sponge by putting it in the microwave for 10 seconds. that doesn't seem like very long....... but would it be possible to sterilize equipment (filters etc) in the microwave? and how long would it take?

i realize this might belong in the basic forum, but it's really a scientific question, ie. i don't want guesses, i want to know "yes", "no", and for how long

thanks
 
I don't think there is anything special about microwaves for sterilisation, they just provide heat a bit quicker than conventional heat sources giving more steam. as for sterilising sponges that was a fad a while back and caused numerous fires, it isn't that effective.
it is possible to sterilise all sorts of things in the microwave however it is so dependent on the power of the microwave how much water is in what you are sterilising etc etc that there is no simple answer

so the scientific answer is yes, no and maybe...
 
Being that most of the bacteria present will contain water, won't most of them be destroyed when their insides turn to steam?

guess I always pictured that happening... can't say I ever really though about if it made sense.
 
I know of parties who have successfully sterilized jars of liquid/honey for mycelium culture. I don't see why it wouldn't work, then again I'm far from an expert in these matters.
 
how much of the radiation are a few million tiny bacteria going to absorb though? the oven would probably burn out before killing the bacteria, maybe putting some water in there too would help with that.

sponges could probably be sterilised if they were damp, a dry sponge seems much more likely to catch fire. i've dried clothes (socks, trousers) in the microwave before, just heat them until they're hot, take them out and flap them around to evaporate as much water as possible, when they stop steaming do it again.

never had a fire doing that but did burn some trousers by not wrapping up some metal bits well enough.
 
How do you rap up the metal bits for microwaving? I didn't realize that was possible.

Even if the radiation didn't directly hit the bacteria- though I imagine the gazillions of photons being thrown out there would easily manage that- the heat would certainly transfer from the water molecules into bacteria.
 
Microwaves are terrible for sterilization because water condenses on the top of the microwave and drips back down, and the insides of microwaves generally are filthy and loaded with bacteria. You are probably increasing the bacterial titer by putting something into a microwave to the point of boiling as the drops condense and fall back into the item being microwaved.

MobiusDick
 
I don't know about you, but I've never, ever had water condense on the roof of my microwave. Are you boiling large quantities of water or have a small microwave? I just tried 2 cups worth, boiled microwaves for 7 minutes, and there was nothing?
 
I'd have thought the fan would take most of the steam out.

Even if the radiation didn't directly hit the bacteria- though I imagine the gazillions of photons being thrown out there would easily manage that- the heat would certainly transfer from the water molecules into bacteria.
Click to expand...

That was my point, if you put a damp sponge in there it'll get hot and probably kill the bacteria. If you put in a dry piece of plastic or glass it shouldn't really get hot and im not sure the bacteria would absorb enough of the radiation to kill them.

About the metal bits, if you take a pair of jeans, fold them at the top so the zip is on the inside then roll them up from the top down you can microwave them without the metal getting too hot and burning the fabric, IME anyway!
 
I've always used a microwave for sterilizing glass vials containing soln intended for parenteral admin (alrthough there are sealed to the outside before they go into the microwave. Just cover with water & microwave until it's boiling. Leave too cool for 10 mins and voila
 
Was going to say don't you risk having it burst but apparently the vapour pressure of water at just under 100 deg C is 1 atm. Can't microwaves create superheated pockets of water though? I've heard that if you microwave water real hot and put a spoon in it, it can kind of explode, i guess from sudden release of lots of steam.
 
^ Yeah, you can, but it requires a really perfect resevoir- I don't think most bowls or glassware would be perfect enough for that.

There's a video of it happening somewhere... I'll see if I can find it. Pretty cool.

Same thing can happen with freezing, but it's not nearly as dramatic.

Here it is.
 
Hehe cool, thats just a beaker though, will it work better if the glass is perfectly smooth and still? Could take the magnetron out and point it at it, save having to move it.
 
Are you sure that water is superheated? It looks more like he adds a spoonful of something to the water to make it explode like that, (Its brown)
 
I expect the stuff added to the water is just providing nucleation sites for bubbles to form.
Boiling stones might work a treat, if this is the case :) .
 
Yeah, it's super heated, I'm pretty sure it's just sand or some sort of powder.
 
Good point, anyone ever forgot to add boiling stones and thought it would be ok to put them in while its hot? You only do that once!
 
It's coffee they use in that demonstration, says so underneath.

Also, orchid breeders (tissue culture) and mushroom growers sometimes use microwave sterilization, but it's risky.

If you combine it with another sterilizer...like alcohol or peroxide, you stand a much better chance of preventing contamination.
 
I don't think you'd want to be adding peroxide to anything you're gonna be shooting...
 
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