Space-Age Cooking

Microwave ovens were probably the first new method for making heat for cooking in more than a million years. In addition, two newer methods have become available for the kitchen. Magnetic induction cooktops have been available for about fifteen years in Europe and Japan and are now becoming known in the United States. And for the modern chef, cooking with light in a “light oven” has been done since the mid-1990s and may become a fad in the immediate future. How do both of these cooking sources work?

Answer

Unlike electric cooktops, which generate thermal energy by the electrical resistance of the burner coils, magnetic induction cooktops generate thermal energy by the magnetic resistance of the metal cooking vessel itself. The 60 Hz AC current flowing in the induction coil beneath the ceramic surface produces an alternating magnetic field than interacts with the Fe atoms for example, in the iron frying pan to oscillate its magnetization 120 times per second. The magnetization direction changes have resistance, so much energy goes into thermal energy in the metal of the pan. Iron and stainless steel pans will work, but aluminum, copper, glass, and ceramic pans and pots will not. The advantages are no noise and no hot cooktop except where the pan has been in contact. Cooking with light is not done by lasers! Light is meant in the broader sense of the word, the infrared (IR) through the visible into the ultraviolet (UV) part of the electromagnetic spectrum. Banks of 1500-watt halogen lamps in the oven walls put out about 70 percent IR, 10 percent is visible light, and the remaining 20 percent is simply heat. The IR is not thermal energy, but when IR is absorbed by molecules, their random motions can be increased. Thermal energy (“heat” in the vernacular) is the random kinetic energy of molecules and atoms. These frequencies penetrate meat only about half an inch at most. Thermal conduction transfers some of this thermal energy farther inside.

However, these light ovens also have a microwave source to penetrate with microwaves to cook the interior of the meat. So while the outside is being browned by the light, the inside is cooking via microwaves. The overall benefit is much faster cooking than is possible in conventional ovens.

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