What about the new thermal-microwave ovens? How do they work? What adjustments must you make?

Sunset, April, 1991

High tech has entered the kitchen, as is apparent to anyone shopping for appliances. And one of the latest innovations is an oven that provides two kinds of energy-thermal (radiant and convection heat) and microwave-at once. This thermal-microwave unit comes in three formats: built-in, free-standing, and countertop. At $1,400 to $3,000, the two larger formats are intended to replace your regular oven (regular ovens typically run from $600 to $900). Countertop versions cost $350 to $500, plug into any outlet, and can supplement your regular oven. How does a new thermal-microwave oven differ from older bake-microwave oven combinations? Instead of switching back and forth between kinds of energy, the new kind can use both simultaneously. This way, it combines the microwave's timesaving advantages with a thermal oven's browning and crisping abilities.

Like bake-microwave ovens, simultaneous thermal-microwave ones are available with radiant heat, convection heat, or both together. Radiant heat is supplied from a heating coil. An oven using only radiant heat has a coil on the bottom for baking and one on top for broiling. A convection oven has an upper coil for broiling; to bake, a fan circulates hot air from the back of the oven. (Convection ovens cook faster than radiant-heat ones, and manufacturers recommend lower temperatures or adjusted cooking times.)

All thermal-microwave ovens can be used for baking or microwave cooking and combination cooking. Most offer a microbroil option, so foods can microwave and broil at the same time-great if you like meats well done and not heavily browned. In addition, tbermal-microwave ovens let you readily preprogram cooking methods. For example, you can set the oven to bake for 20 minutes and then do combination baking (microwave energy plus thermal heat) for 10 minutes. Most models also offer adjustable microwave power levels (you can bake at a selected temperature with a selected level of microwave power). This makes it much easier to control the quality and evenness of the cooking. Adjustments for successful cooking It takes practice to strike a good balance when combining thermal and microwave energy, but you can check and test as you proceed, making adjustments. The most manageable combination to start with is the recommended baking temperature plus 75 percent microwave power. Begin checking for doneness after about a third of the suggested cooking time, and frequently thereafter.

Use the chart below as a guide. To develop it, we tested foods in both conventional and thermal-microwave ovens.

Poultry, meat, fish, most casseroles. We found that these cooked well with thermal and microwave energy used together the whole time. But if microwave level is too high, foods may be tough or overcooked. Baked goods. Ones that change shape or need to develop a specific texture-such as breads, cookies, cakes, pastries should be cooked with thermal heat until they have risen and developed the desired texture. Then you can add microwave energy to finish the cooking faster.

Tougher cuts of meat, dishes containing eggs. Such foods, which need to be cooked more gently, do best at the prescribed baking temperature with 50 percent (or less) microwave power.

Any time you cook with microwave energy, the size (mass) and shape of the food affect the evenness of the cooking. The more food, the longer the cooking time required (2 potatoes take more time than 1). The more irregular the food's shape, the more uneven the cooking (roasts with bones cook less evenly than boned ones). But convection heat, with its fan-driven circulation, helps even the cooking. What cookware to use. In a thermal-microwave, you need cookware that works with both thermal and microwave energy, such as glass or ceramic. F7