The scientists working at the Raytheon Company during World War II were undoubtedly highly stressed. Britain was being attacked by Nazi warplanes and their task was to develop an electronic system capable of tracking the invading aircraft. Rising to the challenge, the researchers came up with “radar,” which helped change the course of the war and made possible the extensive air travel we enjoy today. Lots of coffee must have been consumed during those pressure-packed days at Raytheon, with cups sometimes getting cold as they were left sitting on a bench as the research heated up. But not all the coffee cooled down! Coffee in cups that had been left near the electronic tubes used to produce the microwaves needed for the operation of radar actually heated up. The concept of a microwave oven was born!
Microwaves are a form of low energy electromagnetic radiation. Unlike x-rays or ultraviolet light, they don’t have enough energy to break chemical bonds. They do, however, have the ability to interact with molecules that have positive and negative regions. Water is an excellent example of such a “polar” substance since the oxygen in H2O has a partial negative charge while the hydrogens have a positive character. Just like waves in water, microwaves have crests and troughs. The charged regions of a water molecule align differently with the crests and troughs, which means that as a wave passes through a molecule, it begins to spin. These spinning molecules are jammed so close together that friction is created and it is this friction that generates heat. Microwave ovens therefore work by heating up water. Since most foods have a significant water content, they can readily be cooked by microwaves.
By the 1980s cheap microwave ovens had been developed and began to alter the kitchen landscape. Heating left overs became a snap and fresh popcorn was only a couple of minutes away. But it didn’t take long for the critics to target the novel technology. Microwaves cause cancer, they said. You might as well have a nuclear reactor in your kitchen, one health food advocate declared. That is just plain silly! Microwaves do not break chemical bonds and therefore cannot disrupt DNA, a process essential to carcinogenesis. Furthermore, microwaves are confined to the oven and there are no “residual” waves attacking unsuspecting consumers as the door is opened. Then there was the allegation that microwaves change the chemistry of the food, making it unhealthy. One anti-microwave advocate declared that the force that causes water molecules to spin also rips apart and deforms the molecular structure of the food so “that it is no longer food, it just looks as though it is.” Utter nonsense.
Yes, microwaving does change the chemical makeup of food. Any form of cooking does that. Heat initiates a number of chemical reactions, most of which are desirable.Proteins become more digestible and various flavored compounds are produced. True, microwaved cooking may lead to a less tasty meal since compounds such as thiazole, furan and pyrazine, all very flavorful are not as extensively produced by the lower temperatures and shorter cooking times in a microwave. On the other hand, heterocyclic aromatic amines (HAAs), which have been linked to cancer, are far more likely to form in fried, grilled or broiled meats than in those that have been microwaved.
Spanish researchers recently caused quite a stir when they compared nutritional losses in steamed, boiled and microwaved broccoli. They were interested in levels of flavonoids, compounds which have decided anti-cancer effects. Microwaving broccoli resulted in a 97% loss of flavonoids, while there were minimal losses associated with steaming. Reports in the lay press inferred that this research demonstrated that nutrients are destroyed by microwave cooking. It did no such thing. What it did show was that the researchers have no idea about how broccoli should be cooked in a microwave oven. They immersed the florets in water and cooked on “high” for five minutes! Perhaps they like the texture of disintegrated broccoli. I don’t. The way to cook broccoli is to put just a couple of spoonfuls of water in the bottom of a glass bowl, add the florets, cover, and cook for two minutes. Had they done this, I’d bet that losses would be comparable to steaming. But that doesn’t make for as good a story as “microwaving destroys nutrients,” does it?
Is there any real risk with microwave ovens? You bet! They have a long history of causing terrible eye injuries. The problem, considering the extensive use of such ovens is not huge, but there are at least thirteen cases in the medical literature of people being viciously attacked by microwaved eggs. One of the first such reports appeared in the New England Journal of Medicine back in 1991. A 19 year old man, for reasons known only to him, heated seven eggs in their shells in a microwave oven at full power for five minutes. He managed to remove them from the oven uneventfully, but when he sat down at a table, six of the eggs spontaneously exploded causing severe burning about the face. The problem of course is pressure buildup due to steam inside the egg. Even eggs cracked into a bowl can be dangerous. Several people have been injured when they pierced the yolk of a microwaved egg with a fork. The cooked membrane around the yolk can sustain a great deal of pressure, at least until it is pierced. Then it retalliates by releasing a jet of steam.
Be careful with microwaving coffee as well. Sometimes the liquid can become superheated without boiling. Then when the cup is picked up, the coffee can virtually explode out of the cup. So wait until you see the liquid clearly boiling in the oven before handling the cup. Those researchers at Raytheon may have noted this effect, but probably saw no need to comment on it. After all, they would have never guessed how their work on radar would eventually make waves in virtually every kitchen.