Model microwaved foods to optimize their cooking

Why do some foods, such as eggs, explode in a microwave oven? Why do microwave-heated TV dinners emerge with dried-out peas but frozen mashed potatoes? Why do microwaved french fries always come out soggy? For the first time, Cornell University scientists (Department of Agricultural Engineering, Riley-Robb Hall, Ithaca, NY 14853) have determined the fundamentals of the processes involved in microwaving foods. Their calculations could turn microwaving into a predictable science, resulting in more appetizing and nutritious foods.

Investigators have developed mathematical and computer models to explain how different foods, their shape and size are affected by oven power and placement during microwave heating. They tell us their models provide a quantum leap in understanding how microwaves behave and their change in behavior as heating occurs. They believe their models will enable manufacturers to formulate foods with the most successful size and shape for microwaving and to label products with more accurate and precise microwaving instructions. Their findings also might make microwave sterilization commercially possible for increasing product storage life.

About 95% of American homes have a microwave oven, and food products for the ovens generate sales of more than a $4 billion a year. Many microwave products have failed in the past because foods are heated unevenly and unpredictably. About 90% of new microwaveable food products fail every year.

Cornell's models provide a comprehensive description of what goes on in a microwave oven by linking the electromagnetics, heat transfer and the biochemical changes in heated foods inside the oven. Researchers' calculations also indicate what produces non-uniform heating patterns during microwaving. For example, a frozen block of food does not absorb microwaves very well, but as it is heated and parts of the surface thaw, the thawed regions start absorbing energy. As the outer layer thaws and starts absorbing more and more energy, it serves as a shield, preventing microwaves from getting to the inside of the food. Scientists can now quantitatively predict why certain parts of a product may boil while other parts remain frozen.

In the case of an egg and other round foods, their shape and size may result in their centers being heated first. If the food is dense, the pressure from the developing steam near the center may not be able to escape fast enough and could cause the food to explode. The models quantify these phenomena. Microwaving has not been used on a commercial scale because heating patterns have been too unpredictable.

Within a few months scientists expect to have final calculations computed that relate the properties, the size of a food item and its placement in the oven with what to expect in terms of heating. The calculations also would ensure that heating is more uniform. The project on microwave heating patterns is funded by the USDA and the microwave sterilization project is funded by the U.S. Army.

Further information. Ashim Datta; phone: [phone]; fax: [phone]; email: [e-mail].