How a microwave oven transfers energy into food
A microwave oven sends electromagnetic waves into food. Their changing electric field interacts with polar molecules, especially water, and dissolved ions, transferring energy that becomes heat. The heating can be uneven, which is why a hot edge does not guarantee that the centre of a dish is equally warm.
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Energy absorbed inside the food
A microwave oven produces electromagnetic waves that interact with the food's electrical properties. Polar molecules, particularly water, respond to the changing electric field, while dissolved ions also contribute to energy absorption.
The absorbed energy becomes heat. Microwaves penetrate some distance into food, but they do not necessarily reach and heat every part equally. Heat also spreads by ordinary conduction from warmer regions to cooler ones.
Microwave cooking is not simply heating from the inside out. The pattern depends on the food's composition, shape, thickness and position in the oven.
- A turntable moves the food through different parts of the heating pattern.
- Stirring redistributes warmer and cooler portions.
- Standing time allows heat to spread further.
A thick dish can therefore contain areas at noticeably different temperatures.