Q: A new kind of oven supposedly cooks with light instead of heat. How does it work?
A: So-called light ovens have been in specialized commercial use since 1993 but are only now being produced for home use. A countertop or wall-mounted FlashBake oven manufactured by Quadlux Inc. has been available since December, while General Electric Appliances' built-in Advantium ovens will be available in October to builders and contractors for installation in new kitchens.
When I first heard about the light oven several months ago, my skeptic button was pushed hard. I remembered that when my daughter was a tyke I bought her an Easy Bake toy oven that supposedly baked tiny cakes safely with a little light bulb. It didn't work.
Moreover, some of the promotional statements that I have read about the new light ovens sound like pseudo-scientific hype: They "harness the power of light," cook "with the speed of light" and "from the inside out."
Light does indeed travel, appropriately enough, at the speed of light, but it doesn't penetrate most solids very far. Try reading this newspaper through a steak. How, then, can light deposit enough energy inside the food to cook it, unless it is incredibly intense? I thought of lasers, those ultra-powerful beams of light that we use for everything from eye surgery to annoying the neighbors with little red dots, but their light is so compact and concentrated that at most they could zap one grain of rice at a time.
Ah, but there is light, and then again there is light. The secret of the light ovens appears to lie not only in the intensity of their radiations but in the blend of wavelengths that they generate. I haven't had a chance to test these ovens myself, but here is my analysis of how they work, based on information gathered from a conference call with some of GE's techies.
It's not quite light
And God said, "Let there be visible light, but also ultraviolet, infrared and an entire electromagnetic spectrum of longer and shorter wavelengths." (Not an exact quote.) What we humans call "light" is the mere, thin slice of the solar energy spectrum that our eyes are capable of detecting. In a broader sense, the word "light" really requires more exact specification.
The light ovens contain banks of specially designed, long-life, 1500-watt halogen lamps that are not vastly different from the halogen lamps in many modern light fixtures. But only about 10 percent of a household halogen lamp's energy output is visible light; 70 percent is infrared radiation and the remaining 20 percent is heat. The light ovens' halogen lamps produce a secret mixture of visible light, various infrared wavelengths and heat. It's the combination of all three that does the cooking.
(Regardless of what many science books may tell you, infrared radiation is not heat; it's a form of radiated energy that is converted to heat only when absorbed by an object. I call it "heat in transit." The sun's infrared radiation isn't heat until it is absorbed by the roof of your car.)
The light ovens' visible and near-visible light do indeed penetrate meat to some extent--you can shine a flashlight through your thumb in a dark room. And they aren't absorbed by water molecules as microwaves are, so they can deposit all their energy directly in the solid portions of the food, rather than wasting their energy by making steam first. Some of the wavelengths put out by the halogen lamps can penetrate foods up to three- or four-tenths of an inch. That may not sound like a lot, but the deposited heat then gets conducted deeper into the food from there. And the ovens supplement the light with microwaves, which penetrate more deeply. (You can use them also as independent microwave ovens.)
Meanwhile, the longer-wavelength infrared radiations and the heat are being absorbed in the food's surface, browning and crisping it--something that microwave ovens can't do. Ordinary ovens take a long time to brown food because only some of their heat gets to the food by infrared radiation; the rest has to get there through the air, which is a poor conductor of heat. The light oven's infrared radiation heats the food's surface directly to a higher temperature than an ordinary oven can, so the browning is faster.
Speed, in fact, is the main selling point of light ovens. When GE's market research teams asked what consumers want most in their cooking appliances, the answers they got were speed, speed and more speed. People said they would love to be able to roast a whole chicken in 20 minutes and broil a steak in nine. (To be followed, presumably, by eating over the sink.)
Now a microwave oven can cook a chicken in 20 minutes and a steak in six, but only your dog would want them. Microwaves deposit their energy almost entirely in water molecules, so the cooking is essentially a steaming process. The food's temperature therefore never gets much above 212 degrees. The reactions that make food deliciously brown and crisp during roasting, grilling and broiling don't begin until 300 or 400 degrees, surface temperatures that the light ovens' infrared radiations can easily achieve.
What's really remarkable about the light ovens, though, is their computer technology. A microprocessor driven by proprietary software programs the on-off cycling of the lamps and microwave generator in a carefully worked out sequence for the optimal cooking of each dish. GE's market research discovered that 90 percent of all American consumers' cooking entailed only 80 recipes (no comment), so these 80 recipes are programmed into the oven's data bank for push-button production. Just punch in what kind of steak you have, its thickness and weight and how you want it done, and it's on your plate before you can say "grace."
Now if we only had a computer that would dispense with all of that time-wasting soft music, candlelight, conversation and wine.
Robert L. Wolke is professor emeritus of chemistry at the University of Pittsburgh and the author of "What Einstein Didn't Know--Scientific Answers to Everyday Questions." Send your food or cooking questions to firstname.lastname@example.org.