Radiation: Energy from Radiant Heat and Microwaves

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Radiation is pure energy from within the electromagnetic spectrum from microwaves through to infrared. Atoms in the food absorb this electromagnetic energy directly, then release it as increased atomic motion, which we sense as heat.

Generally, for cooks, radiation is a flame, glowing charcoal or a heated electric element that is glowing red and radiating infrared. Ingredients are cooked by being sufficiently close to the source of radiant heat to be able to absorb heat energy across the space between the two.

Fire is the most basic type of radiant energy. Although relatively inefficient, radiant heat from fire is still used in broiling or grilling and barbecuing. In these methods, the coals heat up to 1090oC (1994oF) and catalyse the browning processes in food to give them a good flavour on the food's surface. Coals or wood are also used in tandoor ovens, old bread ovens especially for flat-breads and similar fuel ovens like clay crocks, where the linings take up the heat energy from the fires within them and then radiate out infrared energy back to the food being cooked.

Microwave ovens also use radiant electromagnetic energy, but at a longer wavelength than the infrared methods above. Microwaves only make polar molecules such as water vibrate and heat up.

Because water heats up only to 100oC (212oF) (boiling point), the food is cooked at a lower temperature than with infrared. Therefore, the food does not go through the browning processes and the food can look pallid and have a strange, almost rotten taste. However, microwaves do get further into the food, so cooking it within the food as well as on the surface. Microwave cooking is best for reheating foods and those cooked in a strong sauce to provide it with decent depths of flavour.

Further Reading

  • Davidson, A. (1999) The Oxford Companion to Food, Oxford University Press. ISBN 0192115790.