This question may sound as stupid as it is, but I just want to feed my curiosity (I am not going to eat mouldy food).

I am trying to find a common point for these two assumptions (provided that both are true):

  1. Many years ago I was told that microwave heating purifies food out of any valuable nutrition values, because microwave radiation plus high temperature kills all biological forms of life (i.e. "good" bacteria) or organic chemistry (i.e. vitamins) that exists in heated food.

  2. About 2-3 years ago I also run through a question asked here (can't find it now) to which answer explained that there are only 2-3 examples of food that can be still eaten after removing mold. All other thousands of food examples must be recycled, if mouldy.

If both assumptions are correct then how it is that treating a food with a little bit mold over it for about 5-7 minutes in microwave at let's say 800 W doesn't do the same (point 1) to mold, which is after all a biological component (fungi?)?

Isn't 5-7 minutes of heat and microwave emission enough to kill all colonies of mold and enough to make food again eatable?

(of course I am talking about "bad grey mold", not "good cheesy blue mold")

  • 3
    There are already answers, which I won't repeat, but a rule of thumb: there is no provision for turning unsafe food into safe food. Once it has passed the time limits, or shown any signs of spoilage, it's final. Since many people don't know these basics, we have written up a short primer in the food safety tag info, which might be interesting: cooking.stackexchange.com/tags/food-safety/info.
    – rumtscho
    Commented Dec 9, 2022 at 16:28
  • 1
    #1 is just nonsense said by people who have no clue how microwaves work. if photons at the frequency of microwaves killed biological lifeforms we'd all be dead as we are constantly bombarded by photons of even higher energy levels (visible light, for one). also, when it comes to nutrition there's no difference between microwaving and heating up the thing with, for example, an oven.
    – eps
    Commented Dec 9, 2022 at 22:39
  • for comparison, a sunbather on a sunny day receives roughly the same wattage of energy as something in a microwave. Microwaves are like the singers who can break glass from singing a particular note. It's not the energy of the note that matters, it's that (like microwave ovens) the frequency is just right, so that the object vibrates extremely rapidly.
    – eps
    Commented Dec 9, 2022 at 22:50

2 Answers 2



In many cases, it's not the mould (or bacteria etc.) itself that poisons you, it's toxins released by the pathogen. Killing the mould doesn't say anything about what happens to the toxins, any more than killing a creature cleans up its excrement. You should assume this to always be the case as even if you could identify the most visible mould as not too much of a threat, you're quite likely to have other forms as well.

It will also taste bad, as you'll know if you've ever bitten into bread that hadn't kept as well as you'd expect, without noticing mould spots.


A microwave is NOT a treatment for mold or food pathogens. It is simply a device that causes the water molecules in food to vibrate producing heat in food. Of course, heat is a treatment for many food pathogens. However, a microwave is particularly tricky here, because depending on where the water molecules are, or other interference, such as bone structure, or density of the product, many foods don't heat evenly in the microwave. Other than producing inconsistent heating, there is nothing special happening in your microwave that will take care of mold or pathogens.

Some molds are edible (think blue cheese). Some problematic varieties can be scraped off the surface without issue. However, molds can grow into products (where you can't see them) and produce toxins. The least risky approach is to discard moldy foods.

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