Whether it is about warming up some leftovers, making some popcorn for a quick snack, or cooking a full-course meal, a microwave always comes in handy. Have you ever wondered how this little box-like machine creates such wonders with food? Have you ever wondered how a microwave works?
When microwave ovens first came in to use in the 1970s, they lifted household convenience to a whole new level. A conventional oven heats food very slowly from the outside, but a microwave oven uses tiny, high-powered microwaves to cook food more evenly from the inside. This is why a microwave can cook meat roughly six times faster than a conventional oven. Microwave ovens also save energy, because food can be cooked immediately without waiting for the oven to heat up to a high temperature first.
Like many great inventions, the microwave oven was an accidental discovery. Back in the 1950s, an American electrical engineer Percy Spencer (1894–1970) was carrying out some experiments with a magnetron at the Raytheon Manufacturing Company when he accidentally discovered microwaves. Microwaves are a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter, with frequencies between 300 MHz (1 m) and 300 GHz (1 mm). Microwave ovens are so quick and efficient because they channel heat energy directly into the tiny food particles. Microwaves heat food like the sun heats water—by radiation. A microwave oven passes microwave radiation at a frequency near 2.45 GHz (12 cm) through food, causing dielectric heating.
Another critical factor is the size and shape of the food item. Microwaves can’t penetrate more than a centimeter or two into the food. If you’re cooking anything large, only the outer layers will be cooked. The interior will be cooked using the exterior layers by conduction. Fortunately, most of the things people cook in small microwave ovens aren’t more than a couple of centimeters across. Unfortunately, since the inside and outside of the food are cooking in different ways, and at different speeds, it’s easy to end up with something that’s cooked on the outside and uncooked in the middle, or overdone on the outside and cooked just right in the middle. Microwaveable dinners specify a “cooking time,” followed by a “standing time” (where you leave the cooked food alone before eating it). During this period, the food effectively keeps getting cooked: the heated parts of the food pass the heat by conduction to the cooler parts, giving uniform cooking throughout.
Despite their small size, microwaves carry a massive amount of energy. One drawback of microwaves is that they can damage living cells and tissue, which is why these ovens are surrounded by sturdy metallic boxes that do not allow the waves to escape. In regular operations, microwave ovens are perfectly safe but like every other cooking method, this method has its drawbacks and takes some getting used to.