# Do Microwave Ovens Kill Bacteria **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [July 16, 2010, 6:12am UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886 "2010-07-16T06:12:03Z")\ **Posts on this page:** 13\ **Page:** 2
**Author:** ![Threbus](https://avatars.discourse-cdn.com/v4/letter/t/73ab20/32.png) [@Threbus](https://boards.straightdope.com/u/Threbus)\ **Post date:** [July 18, 2010, 6:07am UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/21 "2010-07-18T06:07:37Z")
Just to throw out another related subject to argue about 🙂 Bacterial growth is often affected by the pH of the medium. Pizza with tomato sauce would tend to be acidic, and should therefore be a more difficult place for bacteria to survive. Other sauces, especially dairy-based, might allow bacteria to flourish more easily. Toppings could conceivably also alter the rate and quantity of bacterial growth. Regarding pizza consumption: I’m not too picky… but microwave reheating is out! It’s either cold out of the fridge or reheated in a regular oven. CKD, thank you for the welcome note 🙂 ---
**Author:** ![Muffin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/muffin/32/4341_2.png) [@Muffin](https://boards.straightdope.com/u/Muffin)\ **Post date:** [July 18, 2010, 7:27am UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/22 "2010-07-18T07:27:49Z")
> [@Hari\_Seldon](#): > > The only caveat I have on this experiment is that the petri dishes should have been incubated at body temperature. > . . . . > One more caveat, however is that not every bacterium that is harmful in a human body will necessarily grow on an agar medium. It might require a human body environment. Sounds like a typical morning after a frat party, with left-over pizza laying on passed out partiers. ---
**Author:** ![tomL](https://avatars.discourse-cdn.com/v4/letter/t/b782af/32.png) [@tomL](https://boards.straightdope.com/u/tomL)\ **Post date:** [July 18, 2010, 4:05pm UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/23 "2010-07-18T16:05:54Z")
> [@Anthony\_Kaye](#): > > Firstly, there is no doubt that microwaves cannot kill bacteria directly. They can’t even roast ants, as the wavelength of microwaves is greater than the dimensions of the ant, never mind bacteria. Well, I just had to google that assertion, and I was rewarded with this nugget of unadulterated genius: > **[Google Answers: Ants in a microwave oven.](http://answers.google.com/answers/threadview?id=108430)** And the enterprising experimenter reports back: > [@](#): > > For example, an ant on top of a plastic cup in the microwave > oven fairs far worse than one crawling on the oven floor. Microwaves certainly do kill bacteria “directly”, by heating the water in their cytoplasm; they don’t, however, ionize molecules and thus kill by damaging DNA. ---
**Author:** ![Sparky812](https://avatars.discourse-cdn.com/v4/letter/s/eb9ed0/32.png) [@Sparky812](https://boards.straightdope.com/u/Sparky812)\ **Post date:** [July 20, 2010, 3:56am UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/24 "2010-07-20T03:56:48Z")
Funny, once you’ve have food poisoning once, you’ll never take that chance again!🙂 ---
**Author:** ![Tyrannorabbit](https://avatars.discourse-cdn.com/v4/letter/t/41988e/32.png) [@Tyrannorabbit](https://boards.straightdope.com/u/Tyrannorabbit)\ **Post date:** [July 20, 2010, 4:22am UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/25 "2010-07-20T04:22:32Z")
On a related note - a few times, I have heard that “microwaving destroys nutrients”, or some variant of that. This whiffs of crapitude, and stirs in me a mighty urge to tell off the snotty “a microwave is only good for boiling water” people with almost reflexive quickness, but I thought I’d post it to the board first. Are they full of it, or am I? Any takers? ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [July 20, 2010, 4:31am UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/26 "2010-07-20T04:31:19Z")
Just because _you_ don’t reheat pizza in a microwave doesn’t mean that nobody does. I do. ---
**Author:** ![DrHow](https://avatars.discourse-cdn.com/v4/letter/d/3da27b/32.png) [@DrHow](https://boards.straightdope.com/u/DrHow)\ **Post date:** [July 20, 2010, 6:29am UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/27 "2010-07-20T06:29:28Z")
The article says, "The pizza was microwaved … ", which, with the definite article up front, tends to imply that the whole pizza was microwaved. However, 30 seconds or even a minute is no where near enough time to adequately heat up a whole pizza. Since the temperature rise in a microwave oven for a given run time depends on the total amount water in there to heat, some measure of the amount of pizza heated should have been mentioned. I am guessing that it was probably a single slice; but even that is an imprecise measure. The weight of the slice would also have been a relevant thing to mention. Even more relevant would have been to mention something representative of the actual temperature achieved. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 20, 2010, 10:19pm UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/28 "2010-07-20T22:19:25Z")
> [@](#): > > On a related note - a few times, I have heard that “microwaving destroys nutrients”, or some variant of that. Microwaving will destroy some nutrients, but those are the same nutrients that will be destroyed by any kind of cooking at all. And on the other hand, there are some nutrients that can’t be easily digested until they’re cooked. ---
**Author:** ![bigeater](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@bigeater](https://boards.straightdope.com/u/bigeater)\ **Post date:** [July 21, 2010, 2:35am UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/29 "2010-07-21T02:35:51Z")
If you’re such a cheapskate that you would rather risk three or four days of vomiting and GI distress than throw away $3 worth of leftover pizza, then you deserve everything you get. Once food gets to room temp. you have 4 hours AT MOST of safe eating; 2 hours is better. After that you’re playing bacterial Russian roulette. And as the other poster noted, heat won’t eliminate the bacteria’s waste products. ---
**Author:** ![qazwart](https://avatars.discourse-cdn.com/v4/letter/q/5fc32e/32.png) [@qazwart](https://boards.straightdope.com/u/qazwart)\ **Post date:** [July 21, 2010, 4:56am UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/30 "2010-07-21T04:56:45Z")
I use the microwave to sterilize my dish sponges. I put them in wet for two minutes on a turntable on high. After two minutes on the turn table, they’re pretty hot. It gets rid of the mildewy smell. This was recommended to be done daily by either the CDC or the British equivalent. However, the agency changed its recommendation because the sponges could catch on fire. The changed recommendation was daily sterilization via the dishwasher. ---
**Author:** ![Muffin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/muffin/32/4341_2.png) [@Muffin](https://boards.straightdope.com/u/Muffin)\ **Post date:** [July 21, 2010, 5:50am UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/31 "2010-07-21T05:50:40Z")
> [@bigeater](#): > > If you’re such a cheapskate that you would rather risk three or four days of vomiting and GI distress than throw away $3 worth of leftover pizza, then you deserve everything you get. > Once food gets to room temp. you have 4 hours AT MOST of safe eating; 2 hours is better. After that you’re playing bacterial Russian roulette. And as the other poster noted, heat won’t eliminate the bacteria’s waste products. For cold pizza, four hours is not long enough to develop the right flavour. ---
**Author:** ![tomL](https://avatars.discourse-cdn.com/v4/letter/t/b782af/32.png) [@tomL](https://boards.straightdope.com/u/tomL)\ **Post date:** [July 21, 2010, 8:05am UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/32 "2010-07-21T08:05:26Z")
> [@bigeater](#): > > Once food gets to room temp. you have 4 hours AT MOST of safe eating; > … > After that you’re playing bacterial Russian roulette. Wow. You must not get much fruit and veg in your diet. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [July 21, 2010, 2:09pm UTC](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886/33 "2010-07-21T14:09:47Z")
> [@Una\_Persson](#): > > 1000 Watt. > > Edited: vBulletin keeps changing the W to lower case. While the symbol for watt (W) is correctly capitalized, the unit when written out in full need not be. [Cite](http://physics.nist.gov/cuu/Units/units.html). This is true even for units named after people, such as the newton (N), joule (J), pascal ¶, and watt (W). [Previous page](https://boards.straightdope.com/t/do-microwave-ovens-kill-bacteria/546886.md?page=1)