If Percy Spencer had preferred a different kind of snack, it may have set the development of the microwave oven back for years.
If he had brought carrot sticks or a bag of pretzels? He wouldn’t have noticed the effect of microwaves quite so quickly. But he always brought a Payday candy bar to work, which is chocolate with peanuts. His specialty for many years had been magnetrons.
One day in 1945, Percy Spencer was at work at Raytheon Corporation, where he had been employed for 20 years. He was working with magnetrons as usual, doing experiments with microwave radiation. But on that day, he noticed that the chocolate bar in his pocket had melted. Another person might have just thrown it in the trash and gone on with their day. But Percy wanted to know why it had melted.
Specific experiments followed. It turned out that microwaves could pass through some materials and not others.
Not only could they could pass through clothes and melt candy...
They could pass through glass and boil water astonishingly fast.
They could pass through wax paper and pop popcorn.
They could pass through plastic and reheat cold food.
They would go on to revolutionize food preparation for all time.
This guide was authored by John Hutchinson, Fogler Library Business Librarian and Representative for the Patent & Trademark Resource Center. Patent Documents come directly from the United State Patent & Trademark Office Website. The University of Maine Special Collections Department provided indispensable assistance.
Percy LeBaron Spencer was born in 1894, in Howland, Maine, just 25 miles north of Orono. His father died when he was still a toddler, and he was sent to live with his aunt and uncle in South Lincoln. When his uncle died, Percy had to leave school at age 12 to help support the family by working at a spool mill.
When he was 17, he got a job installing electricity at a paper mill in Lincoln. Back then, electricity was just starting to be installed in rural areas, and most companies were willing to hire people with little or no experience and give them on-the-job training.
When the Titanic sank in 1912, Percy was fascinated by the role of radio contact in the rescue efforts. He joined the Navy and got technical training in radio and other technology, He also used his time well and educated himself in many subjects on his own time.
After his Naval service, Percy got a job with the Wireless Specialty Apparatus Company of Boston, and spent the rest of his life working with electronics.
A microwave is a form of electromagnetic radiation, typically in the 300 GHz – 300 MHz range. Microwaves can be absorbed by water, fats, and some other substances.
When you microwave certain foods, the microwaves agitate the water molecules, creating heat and friction from within the food itself, not from the outside like a convection oven.
Percy Spence obtained over 100 patents in his lifetime; almost all of them were in the field of microwave technology. The most noteworthy is Patent #2,495,429 Method of Treating Foodstuffs, 1950. In which he states "one of the objects of my present invention to provide an efficient method of employing electromagnetic energy for the cooking of foodstuffs."
Percy Spencer used his skills in electrical engineering and microwaves during World War Two as well. The same microwave radiation, which would later be used to cook food, was also used for the radar sets to detect enemy aircraft and ships. Radar was invaluable in detecting enemy movements because radar could detect movement at a greater distance than human eyesight. It could also penetrate fog, clouds, and darkness.
Magnetrons generate microwaves. The British government had problems manufacturing magnetrons fast enough for the war effort. They could only make 17 per week. Percy Spencer offered to help revise the manufacturing process. After a complete overhaul of the assembly process, he increased the number of magnetrons completed from 17 per week to 2600 per day!
For this feat, the US Navy awarded him the Distinguished Public Service Medal.
One of the very first experiments that Percy Spencer did with microwave cookery was popping popcorn! When you make microwave popcorn at home, you are recreating this very successful experiment.
In a later experiment, Percy and his team tried cooking eggs with microwaves. The eggs blew up and made a huge mess. So Percy made a new rule: When cooking with microwaves, put the food inside a container so it doesn't make a mess. That advice is as good now as it was then.
The first commercially available microwave ovens were over five feet tall and, in 2023 dollars, cost about $48,000. The only purchasers were restaurants, who quickly found them indispensable. They could boil water faster than a stove and could reheat food. Companies began to develop containers and pre-packaged foods specifically for microwaves.