Tinfoil hats and such.

From A., 22 November 2010, microwaves – are they the devil?

Q: And now for something entirely different, I have a good friend who’s skeptical about using microwaves, concerned about potential changes to the molecular structures of food that might impact them (and, in turn, our health). Fact? Fiction? Otherwise?

A: Thanks for your question. Ah, the microwave doubters. I suppose one of the reasons microwaves freak out so many people is that microwave ovens use microwave radiation to heat food. This is one of those circumstances where a little knowledge is a dangerous thing. To the uninformed I suppose the word “radiation” conjures up images of x-rays and nuclear reactors, ionizing rays that cause all kinds of damage over the short and long term. Radiation, however, encompasses heat, visible light, audible radio, television, and so on. On the electromagnetic spectrum, microwave radiation occupies a position somewhere between long infrared and radio/television.

The electromagnetic spectrum*

In a nutshell, here’s how the microwave oven works. Most food is primarily liquid water (even if it doesn’t seem that way). Liquid water is a polar substance – it has a positive charge on each end (the positive hydrogen ion, H+), and a negative charge in the center (the oxygen molecule, O-2). Electromagnetic radiation – the type of radiation the microwave produces – oscillates in waves. I’m going to oversimplify here, but when certain types of polar substances such as water come in contact with an oscillating electromagnetic field, these substances will attempt to reorient themselves in concert with the oscillation of the wave. This rotation – known as dipole rotation – produces heat.

So, no. The microwave does not, on its own, change the molecular structure of the food, by rearranging molecules, breaking them up, or in any other way. The microwave merely heats the food by inducing the rotation of its water molecules. I mentioned in an earlier post that this action effectively cooks the food at the boiling temperature of water (or, more accurately, at temperatures up to the boiling temperature of water). Accordingly, although microwave cooking is less gentle than poaching – making it unsuitable for cooking proteins – it is ideal for cooking vegetables that can be steamed or boiled. In addition, because water vapor escapes during microwave cooking (as opposed to steaming or boiling), it is a useful cooking method for collapsing cell volume in vegetables such as eggplant. So don’t worry – you don’t need to fear the microwave from a health standpoint.

*Source: http://en.wikipedia.org/wiki/File:Electromagnetic-Spectrum.png