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Cornell food engineers redefine the physics of microwave cooking

NEW ORLEANS -- The microwave oven is not just for popcorn anymore.

Consumers who want fresh microwaved foods that are supposed to be crisp and taste better can look forward to improvement, thanks to new Cornell University studies that show how moisture, heating rate and the food's porosity interact during microwave cooking.

"The microwave is grossly underused," said Ashim Datta, Cornell associate professor of agricultural and biological engineering. "Up to now, as scientists, we haven't really understood much of the physics which occur during the microwave processing of food. This research shows us the quantitative physics as to why microwaved food can be soggy and sometimes unappealing, and also why sometimes excessive amount of moisture can be lost."

Datta, along with Haitao Ni, Cornell graduate student in agricultural and biological engineering, will present "Moisture Redistribution and Loss in Foods Under Intensive Microwave Heating" at the Institute for Food Technologists' annual convention in New Orleans, on June 25 at 4:20 p.m.

In conventional ovens, foods such as baked potatoes are heated from an external source, the hot air, and heated from the outside in. Researchers know that the surfaces of conventionally baked foods are generally hotter than the inside and that moisture escaping from conventionally cooked foods is whisked away by heat as it reaches the surface. That "drying" process accounts for why baked potatoes are crisp and pie crusts are crumbly.

Previous research did not take into account the interrelationship between food structure (porosity) and the internal pressures that develop due to evaporation of water inside the food. Once internal pressure is figured into the water-vapor-time relationship, the whole engineering model of microwave cooking is turned on its ear, Datta said. Internal pressure causes a lot more moisture to reach the surface.

Combined with the fact that more moisture reaches the surface, the air inside a microwave oven stays at room temperature -- preventing the moisture from being dried -- making moisture accumulate near the food surface. This accounts for apparent sogginess, Datta said. With time, the surface of microwaved food has more moisture than inside the food, reverse of that for heating in conventional ovens. When the surface stays very soggy, internal pressure can "pump" water out of the food, causing food to lose excessive amounts of moisture, also leading to poor quality.

Taking food porosity into account, microwave food processors and other food companies can design foods for more desirable quality. For example, processed food products could be designed to be cooked with microwave ovens, to be combined with other ways of cooking, such as infrared heat, hot air, or the use of susceptors -- metalized trays that generate heat from microwaves. (Many frozen pizza products use susceptor technology. The metalized cardboard absorbs the microwaves, creating heat, thus whisking away the moisture.)

"Through understanding the true physics of microwave cooking, companies can use this information to provide better tasting and better texture of food, as well as provide more convenience to consumers by promoting increased use of microwave cooking" Datta said.