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I don't have any pictures. If you microwave leftover egg shells is the salmonella strain killed or not?

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    are these broken pieces of egg shell or emptied whole egg shell? Think you are better off steaming them – user110084 Jun 11 '17 at 18:15
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Yes or no - it depends.

We need to look at the question from two different angles.

  1. Microwaves don't kill pathogens, they create heat that can kill pathogens.
    While it seems basically the same, the important difference is that microwaves heat water, not dry substances. If your egshells are dry, you can microwave them for a long time and they will remain cool. Now add to this the fact that while many salmonella bacteria die after a few hours on dry surfaces, some go into a "hibernating" form that remains viable for weeks, your microwaved dry shells remain mostly unchanged with regards to their infectious potential.

  2. Microwaves do not heat evenly.
    Microwaves are notorious for heating unevenly. They can create hot spots and cool spots during normal use. The former is one of the reasons why baby food manufacturers typically discourage parents to warm baby food in the microwave, the latter is actually linked to various salmonella outbreaks when users heated chicken meat or other leftovers in the microwave without making sure adequate temperatures were reached. [1], [2], [3]

So the conclusion:

You need to make sure there is enough water and enough time involved to kill your salmonella in a microwave. Consider the techniques used for pacifiers and similar baby items: A closed, microwave-safe container and a few tablespoons of water to generate plenty of steam, a minimum time of three minutes once the water boils. What's considered safe for a newborn should suffice for your eggshells, too.

Personally would probably dump the shells in a pot of boiling water instead, if I wanted to be very sure. Or pop them in a hot oven after using it anyway, e.g. after baking bread or cake.

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The actual micro-waves only really interact with the water content in objects. So unless your shells are wet your microwave is not going to interact with egg shells in any meaningful way. That is why the same technology is used on an industrial scale in lumber yards to control the moisture content in wood.

It is also why you get uneven heated food when microwaves are used to heat food with uneven moisture distribution, I believe that to be the case with doughnuts (whether doughnuts are eaten hot or not).

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  • Microbes contain water - but what happens at that scale is probably not well researched yet... Also, fats seem to get heated strongly by microwave energy, not just water... – rackandboneman Jun 11 '17 at 23:04
  • @rackandboneman A microwave is a standing wave that does not heat everything across it's field. If ants are too small to be affected reliably (or can literally fall between the high-energy waves), I don't think I would rely on them having an effect on the water in microbes. – Robert Cartaino Jun 12 '17 at 18:12
  • Yes, if there is a stable standing wave .... I thought in a microwave with a fan and turntable, things were intentionally chaotic? Oh well, entomophagy and microwave ovens are going to be a frontier :) I guess swept frequency designs will be the newest thing then :) – rackandboneman Jun 12 '17 at 19:51

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