A Microwave Heats Water And That Explains Its Failures

A microwave does not heat food evenly and was never able to. It heats water specifically, and every characteristic behaviour follows from that.

The energy targets water molecules

Microwave radiation makes water molecules rotate rapidly, and the friction between them produces heat directly inside the food rather than at its surface.

Fat and sugar respond to a lesser degree, and dry materials such as ceramic, glass and most plastics barely respond at all, which is why the plate stays cool.

That is also why a dry bread roll warms slowly while its damp filling becomes scalding, and why a plate can be cold under hot food.

Penetration is shallow

The energy is absorbed within the outer layer of food and only travels further inward by ordinary conduction, the same as in any other cooking.

So a thick or dense item heats at its edges while the centre lags, and continuing to run the oven overcooks the outside before the middle catches up.

Standing time exists to let conduction even this out, which is why instructions specify it and why skipping it produces a cold core.

Nothing browns because nothing gets hot enough dry

Browning requires a dry surface above the boiling point of water, and a microwave keeps the surface wet by driving moisture outward from within.

The surface therefore sits at boiling point and food emerges pale, soft and steamed regardless of the power setting used.

Combination models add a grill or convection element for exactly this reason, since the browning has to come from conventional heat.

Power settings are duty cycles

Most microwaves have one power output and reduce the setting by switching on and off rather than by emitting less energy.

A low setting therefore alternates bursts of full power with pauses, and the pauses are when conduction evens the temperature out.

Which is why defrosting works better at low power over a long period: the pauses do the work, and full power simply cooks the edges.

Using it for what it is good at

Steaming vegetables in a covered dish with a little water plays to the mechanism exactly, and it is faster and more even than a pan.

Reheating wet dishes works well, particularly stirred partway through, since stirring does by hand what conduction would do slowly.

Anything expected to be crisp, browned or evenly cooked through a thick piece is asking for a mechanism the appliance does not have.