As far as accidental inventions go, the microwave is a pretty good one. Legend has it that Percy Spencer, an engineer with defence contractor company Raytheon, was testing radar magnetrons (a kind of electric whistle that creates vibrating electromagnetic waves) in 1946 when he discovered that the peanut cluster bar in his pocket had melted. Curious as to what happened, he conducted two more tests — one with an egg and another with a kernel of popcorn — and the microwave oven was born.
It would take another 30 years before the microwave would become a staple kitchen appliance in American homes, but the truth of the matter is, Spencer never stopped to think about its safety in food preparation.
“This was when people would wear nuclear stuff around their neck to get rid of cancer,” Spencer’s grandson, George Spencer Jr., told Popular Mechanics.
Despite the microwave’s many detractors — in a column for the Washington Post, food writer Ellie Krieger was on the receiving end of a litany of anti-microwave sentiment, including the insinuation that the ice crystals from microwaved water are influenced by the word “Satan” — it has been given a clean bill of health and safety.
The World Health Organization has stated that “when used according to manufacturers’ instructions, microwave ovens are safe and convenient for heating and cooking a variety of foods.” It goes on to say that the microwaves stay within the oven and leakage is safely limited by design.
But consumers have long struggled with the debate of convenience versus optimal cooking method for nutrition.
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Will the microwave kill off nutrients in your food?
The answer is a little from column yes and a little from column no.
“It’s all relative,” says Keith Warriner, a microbiologist and professor in the Food Science Department at the University of Guelph. “It’s better than boiling, marginally better than steaming and obviously better than frying.”
However, this really only pertains to vegetables.
“It comes down to those high-energy wavelengths, because you can get more rapid heating and cooking in a microwave that will preserve certain vitamins,” he says.
Nutrients like vitamin C and the B vitamins are sensitive to heat and have a certain rate at which they degrade. Therefore, the faster they can cook, the less chance they have of losing their potency. With that in mind, and considering that the best way to cook vegetables for optimal nutrition is by steaming, the microwave is actually your best bet for health.
“If you boil broccoli in a vat of water, most of the nutrients will be leached into the water, but if you cook it at a high temperature for a short period of time in the microwave, you’re retaining virtually all of the nutrients.”
Similarly, an article published by Harvard Medical School states the following: “The cooking method that best retains nutrients is one that cooks quickly, heats food for the shortest amount of time, and uses as little liquid as possible. Microwaving meets those criteria.”
By this rationale, if you’re reheating leftovers, your best bet for retaining any nutritional value is by putting them in the microwave versus heating them up in the oven, which takes longer.
When is microwaving food a bad idea?
This is where Warriner turns what was a commonly held belief about microwaves on its head. Specifically, the notion that microwaves cook from the inside out.
“If you take poultry, for example, a lot of people choose to defrost a chicken in the microwave, but that’s a bad idea,” he says. “It’s a myth that microwaves cook from the inside out. They use high frequency wavelengths to heat the outside of food and the heat radiates inside, much like it does in a traditional oven. As a result, because the microwave has so much energy, it will cook and even dehydrate the surface of the chicken, but it’ll still be frozen inside.”
Warriner references a recent study out of Abertay University in Scotland that states the best way to defrost meat is in the refrigerator as being somewhat misguided.
“To defrost your chicken, you want to do it in cold water, because it’s a constant temperature and has better heat transfer characteristics.”
And while your microwave likely has a defrost button, he says that using that setting to defrost something like a frozen block of vegetable stew will prove just how ill-advised it is to use it to defrost something like a whole chicken.
“You’ll see that it will look defrosted on the surface but inside it’ll still be frozen. It’s OK if you’re defrosting stew because you can stir it to even out the heat and put it back in. But you can’t stir a whole chicken.”
The microwave won’t do anything to rob your chicken (or any other protein) of nutritional value, however. Whether it’s chicken, a steak or an egg, “all it will do is denature them and make them more available to be broken down by our bodies.”
What’s the best case scenario for cooking in your microwave?
Warriner says it’s all about the frozen vegetables.
If you’re still unsure about cooking in your microwave, he says that the next generation of high-tech ovens are in development. They’re called solid state microwaves and they offer really fast and even heating, essentially making issues like surface dehydration a thing of the past.
The only problem is their price.
“They cost about $7,000 now, so it’ll be some time before we see them on the market,” Warriner says. “But Panasonic has put $50 million into a project to create a solid state microwave. Time will tell.”