The chocolate bar that melted next to a radar: the story of the birth of the microwave

D uring World War II, radar became a decisive technology for detecting enemy aircraft and submarines. Behind those systems was a fundamental component: the magnetron , a device capable of generating microwaves. In one of the laboratories of the American company Raytheon, Percy Spencer worked there, a self-taught engineer who would end up finding an unexpected application for that technology.

In 1945, while conducting tests near an operating magnetron, Spencer noticed that the chocolate bar he had in his pocket had melted.

From popcorn to the first oven

His next experiment was with corn kernels. He placed them near the device and watched as they began to pop into popcorn . He then tried an egg, which ended up exploding due to the pressure building up inside it. Those tests gave him a clue: the energy emitted by the magnetron could also be used for cooking.

Spencer then devised a metal box in which to concentrate the microwaves and heat food in a controlled way. Raytheon saw the potential of the idea and filed a patent application for a microwave cooking process in October 1945 . The patent was granted in 1950.

The first commercial model, christened Radarange, reached the market in 1947 . However, it was very far from today’s household appliances : it stood around 1.8 meters tall, weighed hundreds of kilos, and had a high price. Its size and cost initially limited its use to restaurants, industrial kitchens, and other professional spaces.

The technology needed decades of improvements to reach homes. The models became smaller and more affordable, eventually turning that accidental discovery into a common household appliance . Spencer, who amassed more than a hundred patents during his career, did not start out with a project to revolutionize kitchens: he simply noticed a melted chocolate bar and wanted to find out why it had happened.