Hot food, fast: The home microwave oven turns 50

The year 2017 marks the 50th anniversary of the home microwave oven. The ovens were first sold for home use by Amana corporation in 1967, but they had actually been used for commercial food preparation since the 1950s. It wasn’t until 1967, however, that technology miniaturization and cost reductions in manufacturing made the ovens small enough and cheap enough (a still steep US$495; US$3,575 in 2017 dollars) for use in the kitchens of the American middle class. Now, it would be hard to find a U.S. home without a microwave. The Conversation

Amana, a subsidiary of Raytheon corporation, actually called their first model the “Radarange” – a contraction of radar and range (as in stove). What do microwave ovens have to do with radar?

Radar is an acronym for “radio detection and ranging.” Developed prior to World War II, the technology is based on the principle that radio waves can bounce off the surfaces of large objects. So if you point a radio wave beam in a certain direction, some of the radio waves will come bouncing back to you, if they encounter an obstruction in their path.

By measuring the bounced-back radio waves, distant objects or objects hidden from view by clouds or fog can be detected. Radar can detect planes and ships, but early on it was also found that rainstorms caused interference with radar detection. It wasn’t long before the presence of such interference was actually utilized to track the movement of rainstorms across the landscape, and the age of modern radar-based weather forecasting began.

Original cavity magnetron as used to develop radar.
Mrjohncummings, CC BY-SA

At the heart of radar technology is the “magnetron,” the device that produces the radio waves. During World War II, the American military couldn’t get enough magnetrons to satisfy their radar needs. So Percy Spencer, an engineer at Raytheon, was tasked with ramping up magnetron production. He soon redesigned the magnetron so that its components could be punched out from sheet metal – like sugar cookies are cut from dough – rather than each part needing to be individually machined. This allowed mass production of magnetrons, raising wartime production from just 17 to 2,600 per day.

One day, while Spencer was working with a live magnetron, he noticed that a candy bar in his pocket had started to melt. Suspecting that the radio waves from the magnetron were the cause, he decided to try an experiment with an egg. He took a raw egg and pointed the radar beam at it. The egg exploded from rapid heating. Another experiment with corn kernels showed that radio waves could quickly make popcorn. This was a remarkably lucky find. Raytheon soon filed for a patent on the use of radar technology for cooking, and the Radarange was born.

Amana Radarange commercial from 1976.

As time passed and other companies got into the business, the trademarked Radarange gave way to more generic terminology and people started calling them “microwave ovens,” or even just “microwaves.” Why microwaves? Because the radio waves that are used for cooking have relatively short wavelengths. While the radio waves used for telecommunications can be as long as a football field, the ovens rely on radio waves with wavelengths measured in inches (or centimeters); so they are considered “micro” (Latin for small), as far as radio waves go.

Microwaves are able to heat food but not the paper plate holding it because the frequency of the microwaves is set such that they specifically agitate water molecules, causing them to vibrate rapidly. It is this vibration that causes the heat production. No water, no heat. So objects that don’t contain water, like a paper plate or ceramic dish, are not heated by microwaves. All the heating takes place in the food itself, not its container.

Microwaves have never completely replaced conventional ovens, despite their rapid speed of cooking, nor will they ever. Fast heating is not useful for certain types of cooking like bread-baking, where slow heating is required for the yeast to make the dough rise; and a microwaved steak is no taste match for a broiled one. Nevertheless, as the fast-paced American lifestyle becomes increasingly dependent upon processed foods, reheating is sometimes the only “cooking” that’s required to make a meal. Microwave ovens’ uniform and rapid heating make them ideal for this purpose.

Over the years, there have been many myths associated with microwave cooking. But the truth is that, no, they don’t destroy the food’s nutrients. And, as I explain in my book “Strange Glow: The Story of Radiation,” you don’t get cancer from either cooking with a microwave oven or eating microwaved food. In fact, the leakage standards for modern microwave ovens are so stringent that your candy bar is safe from melting, even if you tape it to the outside of the oven’s door.

What’s the deal with metal in the microwave?

Nevertheless, you should be careful about microwaving food in plastic containers, because some chemicals from the plastic can leach into the food. And, yes, you shouldn’t put any metal in the microwave, because metallic objects with pointed edges can interact with the microwaves from the magnetron in a way that can cause electrical sparking (arcing) and consequently damage the oven or cause a fire.

The microwave oven has definitely transformed the way most of us cook. So let’s all celebrate the 50th anniversary of the home microwave and the many hours of kitchen drudgery it has saved us from. But if you want to mark the date with an anniversary cake, best not to cook it in your microwave – you’d likely end up with just a very hot and unappetizing bowl of sweet mush.

Timothy J. Jorgensen, Director of the Health Physics and Radiation Protection Graduate Program and Associate Professor of Radiation Medicine, Georgetown University

This article was originally published on The Conversation. Read the original article.


Top image; 1967 promotional image for the Amana Radarange

Health check: is it safe to microwave your food?

Today every kitchen would seem “under-equipped” without a microwave, with its efficient ability to cook, defrost and reheat a variety of different foods. The handy appliance uses microwave radiation to do so. This is a type of electromagnetic radiation similar to radio waves and infrared light.

Although generally recognised as safe, the internet is awash with articles about the dangers microwave radiation poses to your food. Some claim using microwaves can cause “cataracts and cancer”. Other posts says it “zaps the nutrients right out of your food”.

If you believe this, the “killer” oven in your kitchen must be a terrifying sight, but there is actually no research to support the supposed dangers of microwave cooking. Hopefully we can allay your fears by checking some common danger claims against the evidence.

Does it zap the nutrients out?

Putting raw foods through any type of process – including heating and cooling – leads to changes in their physical properties, chemical composition and nutritional profile.

If nutrients are lost from foods cooked in microwaves, this would be because too high a temperature was used, or they were cooked for too long. The correct combination of time and temperature can help preserve most nutrients while also improving the foods’ taste, texture and colour.

The time and temperature required depends on the type of food. High risk foods such as meat, fish and eggs need to be heated to at least 60℃ to be safe.

Rapid cooking helps preserve beneficial chemicals in green vegetables.

Microwave cooking is unlikely to negatively affect vitamins and other compounds associated with improved health. For instance, rapid cooking actually helps preserve a group of beneficial chemicals, the polyphenols – that increase the total antioxidant activity of foods – in green vegetables.

One study compared microwaving or steaming vegetables, such as cabbage, carrots, cauliflower and spinach, to pressure cooking. It found vegetables that were pressure cooked lost more insoluble fibre, which is good for gut health, than those that were microwaved or steamed.

A key nutrient usually destroyed when cooking vegetables is vitamin C, a severe lack of which can lead to conditions like scurvy. But boiling vegetables accounts for greater nutrient losses than microwaving them. This is because water soluble nutrients are readily leached into water when they are boiled, while very little water is used in microwaving.

Short bursts of heating, such as used in microwave cooking, can retain most of a vegetable’s vitamin C.

Can it give you cancer?

Some of the best studied cancer-causing compounds are the heterocyclic aromatic amines (HCA). These are formed naturally in protein-rich food such as meat and fish during cooking, and are more likely to form if the meat is cooked for a long time and at higher temperatures.

The method of cooking is a major factor affecting HCA formation. Some researchers have reported HCA are formed in chicken at higher levels when cooked in a microwave, compared to when pan-fried, barbecued or baked.

Barbecued fish has higher levels of HCA than microwaved fish.

But no research has claimed or shown an association between regular consumption of microwave-cooked poultry and cancer.

A recent study has revealed barbecued fish contains more HCA than microwave-cooked fish, while HCA could not be detected at all in microwaved beef. Also, thawing beef and re-heating previously-cooked meat or fish in a microwave just for a few minutes, does not produce any extra HCA.

What about the packaging?

There is some evidence to suggest chemicals in plastic packaging can migrate into foods when microwaved, which has been associated with increased risk of cancer.

If your packaging has a microwave safe symbol, it is safe to use in the microwave.

But most of today’s plastic containers, packages and wraps are specially designed to withstand microwave temperatures.

If packaging is marketed as microwave safe, has a microwave symbol or provides instructions for proper microwave use, it is safe for microwave cooking or heating.

Leaching of harmful toxins or “cancer-causing” compounds from appropriately packaged products during microwaving is highly unlikely in Australia, although this area could benefit from more research.

Does it kill bad bugs?

Cooking food significantly reduces the risk of food-borne illness.

A major challenge in microwaving is the unevenness of temperature distribution due to the shape of the food. You may notice when you heat food in a microwave that there are often hot and cold spots. This poses a potential safety issue.

Microwave cooking can only kill disease-causing bugs when the correct temperature and time combination is achieved throughout the food portion. Cooking to temperatures above 60℃ will kill most bugs known to cause food-borne illness, but the toxins produced by them may be heat-tolerant.

Stir food during the microwaving process so the heat is evenly distributed.
Lachlan Hardy/Flickr, CC BY

If the food is already contaminated with bugs that produce toxins, microwaving might kill the toxin-producing bug but not destroy the toxins, despite the correct temperature and time combination. This can also apply to other cooking methods. Appropriate food storage is the key to minimising such risks.

Minimising risk

  • Avoid overcooking vegetables to minimise nutrient losses
  • Before microwaving, check the labelling on the package and follow the instructions
  • If the package is not marked as being microwave-safe, switch to a suitable microwave container
  • Rotate and stir foods during cooking to spread the temperature of heating equally and as such minimise potential for food-borne illness. Check the temperature of food before consumption
  • Remember microwaving cannot magically make contaminated food safe. So if in doubt, throw it out.

The Conversation

Senaka Ranadheera, Early Career Research Fellow, Advanced Food Systems Research Unit, College of Health and Biomedicine, Victoria University; Duane Mellor, Associate Professor in Nutrition and Dietetics, University of Canberra; Nenad Naumovski, Asistant Professor in Food Science and Human Nutrition, University of Canberra, and Robyn McConchie, Professor, Faculty of Agriculture and Environment, University of Sydney

This article was originally published on The Conversation. Read the original article.