PDA

View Full Version : Will a microwave oven kill germs on food?


Elendil's Heir
12-15-2008, 10:03 AM
So say my idiot brother (I don't have one) purposefully sneezes on my pizza. Would nuking the pizza kill any germs, viruses or other bugs he might have left on it? Is there an average length of nuking that will be sure to get the job done?

CookingWithGas
12-15-2008, 10:17 AM
My first impulse was to say that it would kill germs, particularly if they are on the surface of the food, because it will heat up the food as well as the germs themselves, and heat can kill germs. Although there are two more specific questions that should be answered by someone who really knows.

1. Do microwaves directly kill bacteria or virus? If so, how long does it take?

2. How long must bacteria and virus be exposed to heat, either by a hot food surface or by hot ambient air, to be killed? Boiling water kills most germs but some guidelines say to boil for, say, 20 minutes. I believe there are some bacteria that can survive boiling. IIRC anthrax spores are very robust; not sure if they can survive boiling.

It may be that a minute in the microwave, sufficient to heat a slice of pizza, might not be enough to wipe out the germs. And I suppose there are also some differences between what it takes to kill bacteria vs. kill a virus.

Mr Buttons
12-15-2008, 10:18 AM
I'm not sure if the microwave has any particular benefit for killing germs vs a fryer or an oven. Assuming you heat the food properly in any of these cooking appliances, any formerly-live germs will die when the temperature reaches around 180-200 degrees.

sailor
12-15-2008, 10:52 AM
A microwave oven will heat a pizza more unevenly than a standard oven or other traditional heating methods.

jayjay
12-15-2008, 11:25 AM
Besides, I doubt the microwave is going to kill the snot. That would be a trashed pizza if it were mine, even if I could autoclave it.

KneadToKnow
12-15-2008, 11:35 AM
Microwaves heat things by heating up the water in the things. I would expect that a microwave would only be a satisfactory way of killing germs only if you could use it to reliably heat all the water in all the germs and/or the food bearing the germs, to a boil.

And if you could do that, I expect the food wouldn't be something you'd then want to eat, now having no water left in it.

But this is 88% WAG.

Fubaya
12-15-2008, 11:45 AM
The microwave won't kill them but the heat might. One study (http://webmd.com/news/20070124/microwave-kills-germs-sponges) showed that microwaving sponges for 2 minutes in a microwave killed 99% and four minutes killed them all. Ugh, I can't eat a pizza that's been nuked for two minutes, let alone four, and the sponges had to be soaked in water beforehand, I don't know that pizza has enough water in it to work.

I personally wouldn't eat the pizza just because it's gross, however there are more microbes on your hands than there are people on earth, you take in 100,000 with every breath. I wonder how dangerous eating someone's sneezy pizza really is if they aren't currently infected with some highly contagious flu or something.

Squink
12-15-2008, 12:32 PM
Google answers (http://answers.google.com/answers/threadview?id=108430):I got to work this morning a little sleepy and shoved my breakfast in
the microwave oven. After five minutes, it was finished cooking, and
upon removing it, I noticed several ants inside the oven, apparently
unphased by the intense microwave radiation.
...
To understand the reason why an ant survives in a microwave oven is to
understand the way a microwave oven works. A microwave oven emits a
form of energy called ‘standing waves”. That is to say that evenly
spaced, stationary waves of energy bombard the turntable (or plate) in
a vertical fashion so that only specific areas of the turntable are
struck by the waves.,,,
Wiki answers (http://wiki.answers.com/Q/Why_do_ants_survive_in_a_microwave_oven):Microwave ovens heat foods by subjecting them to high frequency (2.5GHz) radio waves that excite the atoms (creating friction) within the foods. A microwave, produces what is called a standing wave pattern. These "standing waves" concentrate the microwave energy vertically at specific points within the oven, most being towards the center and less concentrated at the interior walls of the oven. The reason a microwave oven has a turntable is to rotate the food so that all parts of it pass through one of these standing waves.

Ants, being quite small, are able to avoid these standing waves within the microwave oven, and therefore not get cooked. If an ant was subjected to microwave energy and restrained, so that it could not get out of the heat so to say, it would die.Bacteria can't move as fast as ants, so the question becomes "does the turntable cause every part of the food surface to be swept by standing waves?" That clearly depends on the oven, but I've had several microwaves that left relatively cool spots on the food surface.

engineer_comp_geek
12-15-2008, 12:35 PM
Some people have the idea that microwaves work because of a resonance with water and that microwaves only heat water. This is not true. Microwaves do make water molecules bounce back and forth but it's not a resonance, otherwise microwave ovens would only work at one specific frequency and in reality anywhere from about 2 to 10 GHz will work for heating stuff up fairly well. Microwaves also heat up sugars, fats, and other non-water materials and induce eddy currents in conductive materials that ends up producing heat.

The microwave radio waves themselves are not effective against germs or bacteria, and in fact you can even nuke insects for quite a bit of time and they won't die either. If you nuke a slice of pizza long enough you will kill germs, but only because the cheese will get boiling hot and the heat will kill the germs. The dough will also get rubbery and the entire thing isn't going to be very edible, IMHO.

I'm with jayjay. Just trash the pizza.

ETA: Squink beat me to the punch about nuking bugs.

masterofnone
12-15-2008, 12:55 PM
1. Do microwaves directly kill bacteria or virus? If so, how long does it take?

2. How long must bacteria and virus be exposed to heat, either by a hot food surface or by hot ambient air, to be killed? Boiling water kills most germs but some guidelines say to boil for, say, 20 minutes. I believe there are some bacteria that can survive boiling. IIRC anthrax spores are very robust; not sure if they can survive boiling.

1. Yes, eventually, but to be sure you killed all of them it would take so long that your pizza would probably dry out and light on fire first.

2. Dry heat sterilization requires one hour at 340F or 6 minutes at 370F. This usually assumes a low biological load, such as a clean container. Obviously, the biological load of the pizza is pretty high even before being snotted on, so you'd have to increase the time or temp by quite a bit. You may think the 6 minutes at 370F would not be too bad, but that is 6 minutes after the pizza has reached 370F, not 6 minutes in a 370F oven.

Boiling water kills most actively growing bacteria, but actually promotes the germination of bacterial spores. Three spore-forming bacteria that cause food poisoning are Clostridium perferingens, Clostridium botulinum and Bacillus cereus. Not that any of these are likely in your idiot brother's snot.

To reliably kill spores, you need to put your slice of pizza in a pressure cooker at 250F and 15PSI for 15 minutes.

If you ate the pizza as is, or with a normal amount of re-heating, the most likely result is absolutley nothing if you have a decent immune system. If you want to sterilize it, what you are left with will be even less apetizing than what you start with, as it will be either burt to a crisp, or steamed into a soggy mess.

Personally, I'd swap pieces with my idiot brother when he wasn't looking. :D

Santo Rugger
12-15-2008, 12:58 PM
...there are more microbes on your hands than there are people on earth, you take in 100,000 with every breath... Cite?

Squink
12-15-2008, 01:20 PM
To reliably kill spores, you need to put your slice of pizza in a pressure cooker at 250F and 15PSI for 15 minutes.If you were to try this at home, and report back to us on the taste experince, I'm sure everyone in the thread would owe you a debt of eternal gratitude.

masterofnone
12-15-2008, 01:34 PM
I don't think Fubya is far off on the number of microbes on the hands.

"...depending on the body location and amount of skin moisture, the number of bacteria on the skin surface may range from only about 1000 organisms per square centimeter on the back to more than ten million on the scalp and in the armpit." Microbiology - A Human Perspective Nester, Roberts, Nester p.423

I'd argue that the hands are much closer to 10 million/cm2 than 1000/cm2, as there are way more transient flora on the hands than other areas, and the area between the fingers is relatively moist.

Let's see...

My hands are roughly 10cm x 20cm x 2sides x 2 hands = 800cm2
10,000,000/cm2 x 800cm2 = 8,000,000,000

Wikipedia estimates world population at around 6.7 billion (http://http://en.wikipedia.org/wiki/World_population).

The 100K/breath figure is way off ulness you're cleaning out a damp moldy basement.

masterofnone
12-15-2008, 01:38 PM
If you were to try this at home, and report back to us on the taste experince, I'm sure everyone in the thread would owe you a debt of eternal gratitude.

No thanks, I prefer that nice bacterial tanginess. :)

Rhythmdvl
12-15-2008, 01:40 PM
What about microwaving the germs on a cooking pot?

What if I put the microwave on a treadmill?

A fun experiment: Take a tortilla, put it on a paper towel, and spread a thin layer of shredded cheese on it (you may want to consider dusting with chili or garlic powder, or the flavor of your choice). Put it in the 'wave for a minute or so, then eat it. Science! Yum!

Oh, wait. I forgot to mention looking at the melting pattern first -- as noted in earlier posts, microwaves don't heat uniformly. This is a good (and tasty) way to see where your own 'wave's hot spots are.

Fubaya
12-15-2008, 05:12 PM
Cite?I don't know where I heard the bit about microbes on your hands. A little searching turns up some links (http://google.com/search?num=100&hl=en&safe=off&q=%22microbes+on+your+hand%22&btnG=Search) on microbiology where it's quoted, but not hard data.

I made a mistake with the 100k per breath but I'd wager I'm still right. I was going from memory of a lecture by Craig Venter (http://en.wikipedia.org/wiki/Craig_Venter) in which he talks about sequencing the DNA in the air. After listening to it again he says being in a large room such as the auditorium where he is giving the speech, "sitting here for an hour, you would absorb maybe 10,000 different bacteria and maybe 10 times that in viruses in an hour. If you go outside it's twice that much.." It's not entirely clear, but I'm pretty sure he is talking about 10,000 different species because that's what that whole part of the lecture is about. Given the number of microbes on the body and the fact that the mouth is a place they thrive, I still think 100k has to be close.

I'll find the lecture source later tonight.

clayton_e
12-16-2008, 06:29 AM
One study (http://webmd.com/news/20070124/microwave-kills-germs-sponges) showed that microwaving sponges for 2 minutes in a microwave killed 99% and four minutes killed them all.


I don't care about the germs, I care about eating anything out a microwave that nuked a soaked sponge for four minutes. I can't imagine what weird tastes would forever be in that machine.

I had a itty bitty piece of hamburger that came off a big chunk.. I'm talking a little curly wavy looking piece from a couple pound piece of ground meat that I was defrosting. It fell off the edge of the turning plate and I found it much later as an even smaller crispy black thing barely recognizable. Reason I looked for it? It stunk up the whole kitchen like death for several microwaves.

Rhythmdvl
12-16-2008, 08:24 AM
I found it much later as an even smaller crispy black thing barely recognizable. Reason I looked for it? It stunk up the whole kitchen like death for several microwaves.

For those playing along at home: Don't forget to take the sponge out of the microwave after nuking it.

clayton_e
12-16-2008, 11:44 AM
Well four minutes should make it hot enough to smell somethin' funky.. Who knows for how long.

Fish
12-16-2008, 11:56 AM
2. Dry heat sterilization requires one hour at 340F or 6 minutes at 370F. ... You may think the 6 minutes at 370F would not be too bad, but that is 6 minutes after the pizza has reached 370F, not 6 minutes in a 370F oven.
For the record, this is far, far, far hotter than food usually gets. (http://cooksrecipes.com/tips/meat-cooking-temperature-chart.html)

Chicken is often cooked to an internal temperature of 165-175F, beef to 140-145F, and pork to 160-170F.

If you cooked all your food to a temperature of 370F it would be like leather. But it would be sterile.

Fubaya
12-16-2008, 06:17 PM
I'll find the lecture source later tonight.here (http://longnow.org/projects/seminars/) it is, scroll down to Craig Venter and snarf the mp3 if interested. Very fascinating stuff.

Best Topics: fake swan us president phd grow horsetail ball peenhammer sex beautiful domestic housewife ear wax taste prominent clavicle buy cabin cruiser bullfighting spears vidangel wiki mother russia meaning elvita adams story mona bone jakon hank hill's dad strip shopping centers black semen cashews poisonous 1mc navy dragon armor military aaa sticker placement slash pairing pennsylvania initials spices for omelets southpark bono peace corps cia does ammonia evaporate bending unit uncirculated denver penny computer makes buying a new car in massachusetts my cat keeps farting whack fol the daddy o received package for someone else usps drinking games to play in the car get receipt from amazon king of the hill buckley best time to drive through chicago 5 cylinder chevy engine how many volts are in a power line best way to reheat fries in microwave cannot find brother printer on network world's most awesome flea market long tail blue jay how to get rid of old checks drano clogged my drain how to pronounce brillouin is daryl hall gay who else died on the same day as michael jackson how long does walgreens keep prescriptions venomous snakes in nh signs of water in your gas tank what glue to use for bookbinding is a piano a string instrument how much diphenhydramine will kill you hot water without gas a=b b=c a=c unlimited music downloads per month csc laundry card reload how tall is arnold schwarzenegger in feet violets are not blue where is your god now movie quote