The Fascinating History and Evolution of the Microwave Oven

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The microwave oven is now a ubiquitous household appliance, with over 90% of American households owning one. However, few people know the captivating history behind the development of this revolutionary cooking technology.

Key Takeaways

1. Percy Spencer accidentally discovered microwave cooking in 1945 when a candy bar in his pocket melted while working near a magnetron.
2. The first microwave ovens were enormous, cost prohibitive devices used commercially, not in homes.
3. Key innovations like cavity magnetrons, solid state controls, and safety interlocks allowed smaller, affordable countertop models.
4. Microwaves rapidly heat food by exciting water molecules that generate thermal friction, not by heating from interior out.
5. Despite myths, microwave radiation cannot escape the interior or harm you when operating.
6. Nutrient retention in microwaved food is equal or better than conventional cooking.
7. Metal objects like foil cause arcing and damage and should never be put in a microwave oven.

Accidental Discovery Leads to Microwave Cooking

It all started with a serendipitous discovery in 1945 by an engineer at Raytheon Corporation named Percy Spencer. He was working on building magnetrons, vacuum tubes used to generate microwaves for radar equipment. One day while working near an active magnetron, he noticed a peanut candy bar in his pocket had started to melt. Intrigued, Spencer started experimenting by aiming microwave energy at food like popcorn kernels and eggs, discovering they cooked much faster than conventional heating methods.

He constructed a metal box with an opening into which he fed microwave power, inventing the first true microwave cooking oven. The heatmap generated allowed the food to be heated evenly and quickly. Raytheon filed a patent for Spencer’s microwave cooking invention on October 8, 1945.

The First Microwave Ovens – Large and Expensive

In 1947, Raytheon built the first commercially available microwave oven called the Radarange. It stood 5’6″ tall, weighed around 750 lbs, and cost over $5,000 (around $50,000 today!). Unsurprisingly, it was too large and expensive for home use. Instead, restaurants, ocean liners, and other commercial operations installed them for food preparation.

The first domestic microwave oven was introduced in 1955 but still cost over $1,000. By 1967, the price had dropped to $495 ($3,500 in today’s dollars) – still outside most home budgets. It wasn’t until technological improvements in the 1970s that microwave ovens became both affordable and small enough for home kitchens.

Key Microwave Oven Innovations

Several important innovations transformed bulky, costly microwave ovens into convenient cooking appliances for the average household:

  • Cavity magnetron – The discovery in the 1930s that allowed generating high-power microwave radiation
  • Short cavity design – A more compact interior cavity reduced size substantially
  • Lower wattage – Newer magnetrons reduced power consumption and price
  • Electronic controls – Replaced knobs with keypads for programming cooking times/power levels
  • Safety interlocks – Prevents microwaves leaking out when door opens

These advances allowed companies like Sharp, Amana, GE, and others to manufacture affordable “counter-top” sized microwave ovens.

The Microwave Oven Goes Mainstream

By 1975, microwave oven sales surpassed gas ranges. In the 1980s, owning a microwave was almost universal in American households. Prices dropped to under $100 for basic models. New features emerged like auto-cook menus, sensors, and inverter power supply for more even heating.

Today, microwaves are produced by major appliance companies and remain a staple for quick cooking and reheating food. Modern models have child safety locks, smart sensors, and convection heating capabilities. While styling and features have evolved, Percy Spencer’s 1945 discovery remains the basis for all microwave ovens.

How Do Microwaves Cook Food So Quickly?

Microwave ovens contain a magnetron that generates microwave radiation at a frequency of 2.45Ghz. This energy is absorbed by polar molecules like water, fat, and sugar which heat up through molecular friction.

Food contains varying amounts of water – lean meats vs veggies for example. Microwaves excite water molecules quickly, transferring thermal energy deeply into food. Conventional heating relies on external heat penetrating inward more slowly.

That’s why microwaves can cook foods like a potato in a few minutes compared to an hour in the oven. The rapid vibration of molecules produces friction that instantly heats the food.

Common Myths and Misconceptions

Despite their ubiquity in households worldwide, people still have some misconceptions about microwave oven safety and function. Let’s examine and debunk some of the most common myths.

Microwaves Cook from the Inside Out

Myth: Food cooks from the “inside out” when heated in a microwave oven.

Fact: This is false. Microwave energy actually penetrates and heats food quite evenly throughout the entirety of the food. While the inside of thicker foods may retain more heat initially, there is no cooking exclusively from the interior outward. The rapid vibration of water and fat molecules happens relatively uniformly through the food.

Standing Near a Microwave is Dangerous

Myth: Microwave radiation can leak out and harm you if you stand close to an operating microwave oven.

Fact: This is completely false. Microwave ovens have thick metal casing that prevents any radiation from escaping. This functions as a Faraday cage to contain the energy. Also, the glass plate and sealing on the door prevent leakage. There are safety interlocks that immediately disable the magnetron if the door is opened.

Microwaves Destroy Nutrients

Myth: Cooking food in a microwave destroys more nutrients than conventional cooking.

Fact: Extensive studies have shown this is untrue. Microwaved food retains its vitamin and mineral content as well as or better than other cooking methods. The extremely rapid heating actually preserves nutrients that would be lost in slower cooking. The lower moisture loss also helps retain vitamins.

It’s Safe to Microwave Metal

Myth: Small metal objects like forks or foil are okay to microwave.

Fact: Absolutely false. Metal objects like utensils, foil, or twist ties can reflect microwave radiation and cause arcing, sparks, and damage to the oven. Only microwave-safe materials like glass, ceramic, and plastic should be used. Metal cookware like aluminum foil should never be microwaved.

Plastic Containers Leach Chemicals

Myth: Chemicals from plastic containers and wrap leach into food during microwaving.

Fact: Microwave-safe plastic containers have been extensively tested by the FDA and do not leach chemicals when used properly. Do not microwave plastics not labeled microwave-safe.

By understanding the real facts behind these common myths, you can use your microwave oven safely and utilize it for fast, convenient cooking.

Microwave Usage Tips

  • Arrange food in a ring pattern for even heating
  • Cover food to retain moisture and prevent splattering
  • Adjust power levels for optimal results
  • Allow standing time for food to finish cooking
  • Use microwave-safe cookware like glass or ceramic
  • Ensure adequate ventilation


Who invented the microwave oven?

Percy Spencer, an American self-taught engineer, while working on magnetrons for radar systems in 1945. He constructed the first true microwave oven after noticing melted candy in his pocket.

When did microwave ovens become affordable for homes?

In the 1970s, technological improvements like solid state electronics and lower wattage magnetrons allowed companies to manufacture much cheaper and smaller countertop models.

What makes microwaves able to heat food so quickly?

Microwaves energize water, fat and sugar molecules in food at the atomic level, producing rapid molecular friction that heats the food instantly.

Is microwave cooking safe?

Yes, microwave ovens utilize Faraday cage shielding to contain radiation safely. Plus, safety interlocks disable power when the door is opened.

Can metal go in a microwave oven?

No, metal objects cause arcing and damage due to reflection. Only microwave-safe materials like glass, ceramic and plastic are recommended.

The microwave oven has revolutionized home cooking. With origins in World War 2 radar technology, this ingenious appliance has become an essential time-saving kitchen tool. Though the basic operating principles remain unchanged, microwave ovens continue improving with smart features and faster reheating.


  1. Smithsonian snapshot: Microwave Oven
  2. Wikipedia: Microwave Oven
  3. Facts and History of Microwave

By Rosie Elliott

I’m Rosie. I’m a professional chef with experience in Western, Mediterranean, and Italian cuisine. I’ve been cooking for over 15 years, and I have two daughters that keep me busy!

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