The greatest discovery since fire

‘The greatest thing since sliced bread,’ is an accolade often bestowed on an invention. However, it never seems to surpass the actual invention of sliced bread. But an invention now found in almost every home in the Western world was introduced as ‘the greatest discovery since fire’. Now that’s an accolade.

Percy Spencer, a self-taught scientist, was working in Massachusetts for Raytheon, a company that made radar equipment for military use. In the 1940s, Raytheon was the largest electronics manufacturer in the USA.

One day, Percy noticed that a chocolate bar in his pocket melted when he stood close to a magnetron, which generates the radio signals at the heart of a radar set.

Rather than ignore the chance observation of his chocolate-bar mishap, as others had done when engineers had warmed themselves by stacks of magnetrons, Percy sprang into action. He wanted to know whether other foods could be cooked by the magnetron’s emitted high-frequency radio waves – known as microwaves. He succeeded with popcorn and even an egg.

Percy applied in 1945 for the first patent for a microwave oven, which he envisaged would cook food as it moved on a conveyor belt through magnetron waves. But cooking wasn’t the only use he saw for microwave ovens. He imagined it would one day be used for a wide range of applications, from ink drying to tobacco curing.

His notebooks record his culinary exploits. Potatoes cooked in a minute – ‘the flavour was good but the potato was not crisp.’ Brussels sprouts cooked for 1 minute 15 seconds – ‘the flavour was dry and not good.’ He lamented that ‘steak doesn’t brown.’

In 1947 Raytheon produced the first commercial microwave oven. A staff competition came up with a name: the Radarange. This was a monster device. It was almost two metres high, one-metre-deep and wide and weighed 340 kilograms. The Radarange blasted out three times the microwave energy produced by today’s ovens. It needed water pipes to keep it cool. At $40,000 in today’s money, the Radarange was not something that was going to catch on quickly in a domestic kitchen.

The first home microwave oven was on sale in 1955, but at half the cost of a Radarange it was still not cheap enough to make an impact.

However, the technology developed rapidly. In 1967, Raytheon launched a sleek, elegant microwave oven onto the market. The time was right – many households now had two working parents, and ready-made meals or reheating had become the way to make dinner.

By the late 1970s, prices had fallen sufficiently to bring the ovens within reach of everyday kitchens. By the 1980s, they had morphed from expensive curiosity to cheap kitchen necessity in a hectic world. Microwave ovens are now in most American and Australian kitchens. There are more than 200 million microwave ovens in use around the world today.

How it works: Turn up the radio

People have used radiation to heat and cook for millennia – sunlight emits radiation at visible (and other) wavelengths; our ancestors used the visible and infrared radiation from fires to cook and stay warm; and electric ovens cook using radiation from a metal element rather than a gas flame. Radiative heat cooks food from the outside, penetrating food through the process of conduction.

Microwaves, radio waves with much longer wavelengths, penetrate food and set water, sugar and other molecules in motion. Molecular motion is what creates heat, so this considerably reduces the cooking time.

Invention of the microwave epitomises a common story in the development and application of technology. A visionary researcher asks a question that no one else has asked. In Percy Spencer’s case, it was ‘will this thing cook an egg?’. He investigated. The answer was ‘yes’. The engineers got cracking. Innovation and mass production drove down the price.

It took decades, but Percy’s perseverance changed our kitchens for ever.

What’s your favourite invention?