Every point you made is counter to the literature I've seen, which is certainly not exhaustive. I have no personal experience to challenge either side of the argument, but the published analyses make sense.

Starch itself does not absorb much microwave energy. But starch contains about 10% moisture that accounts for the easy heating. If you dry your starch to bone dry first - overnight at 60°C will do it pretty well - you'll find it heats much less readily.

If I get time this evening I'll collect the data on ice melting and prove that one. Another fun and easy experiment would be to put two identical, insulated glasses of water into the microwave, one as cold as possible and the other tepid. Heat for 2 minutes and measure the ∆T of the two glasses. The warm one will have gained more than the cold one.

 

Starch itself does not absorb much microwave energy. But starch contains about 10% moisture that accounts for the easy heating. If you dry your starch to bone dry first - overnight at 60°C will do it pretty well - you'll find it heats much less readily.

Pity your sources don't go in for experimental verification.

Any small % water would have been driven off in the first 100 heatings on my starch bags.

Afeter some 5,000 or so reheatings I can experimentally report that the wheat bags are as good as ever. (Although the bags themselves may burn if you are not careful).

I will supply the recipe if you like, but be aware you need a seamstress to complete the job.

 

Starch and grain containing it will hydrate itself to ~10% if exposed to ambient conditions. So while you might drive some of that off, it will quickly return.

 

Starch and grain containing it will hydrate itself to ~10% if exposed to ambient conditions. So while you might drive some of that off, it will quickly return.

How quickly?

You have no idea how my girls use these bags.

Anyone would think jumpers had never been invented.

 

Right, and crystals absorb far less microwave energy as a result.
A microwave oven transfers energy to water by rotating some of the molecules in the field. If they don't rotate, they don't absorb energy from the field.

Right, they don't have to spin or rotate to absorb energy. A stretch or compression of the molecule even while locked as a whole in a lattice is the equivalent of a displacement current. But what it usually does is to limit the direction that energy is absorbed by polarization so it won't heat as fast as water that can absorb energy efficiently in any direction of a changing field with the viscosity of the fluid giving it possible rotational inertia across the material.

 

I want to say yes, but I think we're all hung up on different meanings of "resonance".
...

I definitely am!

If 650W at 2.4GHz makes the water hot because the 2.4GHz is some "resonant" freq of water, then how hot will the water get when exposed to;
650W 2.1GHz ?
650W 2.75GHz? etc

because to my way of thinking if "resonance" was a significant part of the heating effect then it would be easily demonstrated by heating being REDUCED by shifting the freq away from the resonant freq or its main harmonics.

And if the freq does not matter much at all, then it can't be "resonance" it is just "movement" caused by lots of energy.

 

I found this article to be a decent description, in-depth but still readable. This link is so-so.

"Resonance" is really the wrong term to describe what's going on, as it implies some sweet spot in a frequency-dependent process. That's not really right. The microwave frequency is a compromise of penetration (goes down with higher frequency) and effectiveness (goes up with higher frequency).

 

I'd like to explain.
The water molecule is a dipole. Because the oxygen nucleus strongly attracts the electron cloud of molecule to it.
The water molecule has a rotating motion.

Imagine something with the charge plus and minus in its ends that rotates.

It can interact with an externally applied electric field.

Let's take a swing example that swings to a certain frequency.
I can push it with a lower or higher rhythm. Only when I push it in its rhythm I accelerate it most.

Equally at rotation to resonance, the frequency of the applied field must be similar to the frequency of rotation of the molecule.

equations:
Search for Maxwell equation conduction sigma
Dielectric gamma dispersion

The resonance frequency of the water molecule depends on the molecules around which slows it down.

Pure water has resonance frequency at 10GHz.

If we want to calculate how much energy the water absorbs from the external electromagnetic field:
- how much energy actually reaches the water molecule after absorption into the substance around it.
- which is the frequency of water resonance in that fluid
- what percentage is absorbed from the field applied locally.


Biological materials respond to electric field and very little to magnetic field.
On mobile phones, SAR is used to measure the energy absorbed on Kg