Can Microwave Waves Kill Bacteria?

If we take a slice of pizza that has been on the table for some time and put it in the microwave for one minute, will all the bacteria die, and can thus reduce the likelihood of food poisoning, or are we just eating hot bacteria?

This question has several components: microwave oven, pizza, food poisoning and death, and even eating sizzling bacteria.

Before we get started on this topic, let’s look at three important questions: First, can bacteria actually get on food while it is on the table? Second, what is the best way to kill bacteria? Third, is the microwave a suitable bactericide (killing bacteria) tool?


The first question is easy enough to answer.

Yes, bacteria are not only found on floors, countertops, and other surfaces, they also drift in the air. Scientists from San Antonio and Austin, Texas, collected air samples for 17 weeks and found 1,800 species of bacteria in them. Among them were the Francisella tularensis “cousins”, also known as potential biological weapons. I agree that Texas is known for its variety of lower life forms, but still, the results of the above experiment should be considered, especially if the food storage conditions in your home are not good enough.

The next issue is killing bacteria.

Alcohol, which is always doing its job, can make pizza lovers think the problem is solved. Unfortunately, the concentration of alcohol needed to kill bacteria has a long way to go, causing direct harm to your body. Isolating bacteria from oxygen can kill some of them, but, for example, anaerobic bacteria can do just fine without it.

The best way to kill bacteria is by heating. Milk, for example, is pasteurized by heating it to about 162 degrees Fahrenheit (72.2 degrees Celsius) for 15 seconds. But even this does not solve the problem – some bacteria thrive at temperatures up to 167 (75) degrees, and some bacterial spores, such as Clostridium botulinum (responsible for the deadly toxins of botulism), can live for an hour at temperatures equal to 212 (100) degrees.

Can Microwave Waves Kill Bacteria?

Sure. Microwaves use electromagnetic radiation to heat the water molecules in food. It’s heat, not microwaves, but it’s deadly; the hotter you make your food, the more likely you are to kill bacteria in it. (Some have argued that microwave energy itself is deadly to bacteria, but this has not been proven.) The idea is to heat food evenly over a long period of time. If it does not heat up evenly, then the biggest disadvantage of a microwave oven is that some bacteria can survive.


It’s time to do our own experiments. My friends decided to proceed as follows:

  1. They took 30 Petri dishes containing agar (bacteria nutrients), plus an impressive collection of flasks and other laboratory equipment.
  2. I ordered “Meat Lovers” pizza from Pizza Hut. Immediately after delivery, three swabs were taken from the pizza and placed on Petri dishes. The rest of the samples were diluted 1:10 to 1: 100 with distilled water and placed on two more pairs of cups for a total of seven samples, in case there are so many microbes in the clean pizza samples that they cannot be counted individually. …
  3. Then they left the pizza outdoors for four hours. Then the other three swabs that were taken from the pizza were placed on Petri dishes, like the previous ones in a ratio of 1:10 and 1: 100, for a total of seven additional samples.
  4. The pizza was then reheated in a 1000-watt microwave oven at the highest temperature for 30 seconds. Seven more samples were taken.
  5. Then the pizza was kept in the microwave for another 30 seconds. Received seven more samples.
  6. Control samples were taken from distilled water and air.
  7. Petri dishes were placed in sealed bags to prevent evaporation of moisture and were kept for one week at a temperature of 75 (23.8) degrees. Then the experimenters checked for the presence of bacteria. Here are the results that were obtained:
  • Undiluted samples from freshly delivered pizza contain 11 groups of bacteria. Since we cannot change these samples, we will consider them as the basis for a normal, as a rule, a harmless bacterial infection.
  • Samples obtained from pizza left outside for four hours contained 28 groups of bacteria; two more were found diluted 1:10. They are probably harmless too, but my guess is that tripling the number of bacteria triples the risk.
  • Samples taken after 30 seconds in the microwave contained 17 groups of bacteria; 60-second samples are only three. Diluted and control samples did not contain bacteria at all.


Conclusions: (1) Heating the pizza for 30 seconds in the microwave was relatively ineffective. (2) heating it for a full minute killed most bacteria, but not all. As our research budget was exhausted, we decided not to carry out additional experiments, but I suspect that heating the pizza for at least two minutes in the microwave can ensure the disappearance of 100 percent of the bacteria, while at the same time, it may make the pizza inedible. (3) Fresh pizza undoubtedly contains its share of microbes, of course, mostly harmless, but nevertheless, you never know for sure.