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Author Topic: do microwaves kill bacteria?  (Read 16111 times)

paul.fr

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do microwaves kill bacteria?
« on: 18/08/2007 23:41:01 »
If i put my dishcloth, or food perhaps, in a microwave oven. Would it kill the bacteria? yes, no, why, why not.


 

another_someone

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do microwaves kill bacteria?
« Reply #1 on: 19/08/2007 00:05:22 »
Microwaves do not have a direct biological effect in the way that X rays have, but they do generate heat, so putting a wet dishcloth into a microwave will have the effect of boiling the water in the dishcloth (will have far less effect if the dishcloth is bone dry), and this is the same as boiling the dishcloth in any other context.
 

Offline JimBob

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do microwaves kill bacteria?
« Reply #2 on: 21/08/2007 02:25:52 »
It is size dependent. There are bacteria - single cells - visible with the naked eye. If the bacteria is smaller than the microwave wave leingth, then no - if it is larger yes, it wil bounce around as if it were in a poodle. I really loved that dog, too.  [V]
 

Offline DoctorBeaver

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do microwaves kill bacteria?
« Reply #3 on: 31/08/2007 07:38:39 »
It is size dependent. There are bacteria - single cells - visible with the naked eye. If the bacteria is smaller than the microwave wave leingth, then no - if it is larger yes, it wil bounce around as if it were in a poodle. I really loved that dog, too.  [V]


 

Offline Seany

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do microwaves kill bacteria?
« Reply #4 on: 03/09/2007 13:39:06 »
If you shove milk (in a glass of course) in the microwave.. Apparently it kills all the good bacteria and stuff too?
 

Offline MooseHole

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do microwaves kill bacteria?
« Reply #5 on: 14/09/2007 23:30:58 »
Yes, but it makes you sleep better.
 

Offline Quantum_Vaccuum

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do microwaves kill bacteria?
« Reply #6 on: 24/09/2007 04:51:03 »
Actully, sticking stuff in the microwave will excell the growth of bacteria, because it will heat all of the surrondings, and any bacteria that is already their will grow at rapid speeds, but if you heat something up that was in the fridge, or freezer, there wont be much bacteria because the cold will either slow down (fridge, or completely stop (freezer) the growth of bacteria
 

another_someone

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do microwaves kill bacteria?
« Reply #7 on: 24/09/2007 04:59:00 »
Actully, sticking stuff in the microwave will excell the growth of bacteria, because it will heat all of the surrondings, and any bacteria that is already their will grow at rapid speeds, but if you heat something up that was in the fridge, or freezer, there wont be much bacteria because the cold will either slow down (fridge, or completely stop (freezer) the growth of bacteria

As you say, a fridge will not kill the bacteria, but only slow down its growth, so bacteria that were there before will still be there afterwards.

Putting things in the microwave on a low temperature (to defrost) will not kill any bacteria, but will speed up its growth; but heating up in a microwave to boiling point will kill just as many bacteria as if you had boiled the food anywhere else.
 

Offline Quantum_Vaccuum

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do microwaves kill bacteria?
« Reply #8 on: 24/09/2007 05:10:16 »
 Oh, so does that mean that over 100 degree C. every bacteria is killed?
 

another_someone

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do microwaves kill bacteria?
« Reply #9 on: 24/09/2007 12:52:12 »
Oh, so does that mean that over 100 degree C. every bacteria is killed?

There are two different issues.

The vast majority of bacteria are killed at 100C, but there are a small group of exotic bacteria (called thermophiles) that are quite happy to live at temperatures up to 140C (maybe even higher), but these are not normally bacteria responsible for most infections (a bacteria that can thrive at 140C is not normally one that is optimised for living within the human body, which is normally at 36C).

The second issue is that while some bacteria can live in very hot water (i.e. water above 100C that is under pressure, and so is not boiling), they cannot as easily survive steam at 100C.
 

Offline Quantum_Vaccuum

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do microwaves kill bacteria?
« Reply #10 on: 25/09/2007 00:37:07 »

There are two different issues.

The vast majority of bacteria are killed at 100C, but there are a small group of exotic bacteria (called thermophiles) that are quite happy to live at temperatures up to 140C (maybe even higher),


Oh yes, I remember one of my 7th grade science teachers talking about this to us, they find those in the poles, and i think they found a living one on one of Jupiter's or Saturn's moons, so it would be reasonable that they could also live in much colder temperatures as well.

Is there any low temperature that is so cold it kills these "thermophiles" not including,
0 Kalvin?
 

another_someone

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do microwaves kill bacteria?
« Reply #11 on: 25/09/2007 00:47:53 »
Is there any low temperature that is so cold it kills these "thermophiles" not including,
0 Kalvin?

There is no minimum temperature that will guarantee killing all bacteria.

In order to function, bacteria need liquid water, so if they do not have liquid water, they may still simply become dormant until the environment improves.  The key problem with bacteria (or any cells) is the buildup of ice within the cell that can burst the cell wall; but some organisms contain various kinds of anti-freeze that, even if the water freezes, it is prevented from crystallising, and so will not burst the cell wall.
 

Offline Quantum_Vaccuum

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do microwaves kill bacteria?
« Reply #12 on: 25/09/2007 00:55:52 »
So if i used freezing point depression would that mean that bacteria could survive in water that is about -30 Celsius?
 

another_someone

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do microwaves kill bacteria?
« Reply #13 on: 25/09/2007 01:08:05 »
So if i used freezing point depression would that mean that bacteria could survive in water that is about -30 Celsius?

For many bacteria, yes (although it will also depend on how you depress the freezing point - for instance, adding salts to reduce the melting point could themselves be harmful to some bacteria, but not to others).
 

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do microwaves kill bacteria?
« Reply #13 on: 25/09/2007 01:08:05 »

 

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