The finer points of microwave cooking

Sunset, Nov, 1996 by Linda Lau Anusasananan

Zap - turkey leftovers are steaming for lunch. Zap - your vegetables are rewarmed just before you sit down to the big dinner. Cooking or heating in a microwave oven is fast, neat, cool, and easy enough for children to manage. As a result, microwave ovens have become so much a part of our lives that many homes have more than one, and the ovens are put to use every day - if only to reheat coffee. And, come the holidays, it's hard to imagine entertaining without one.

Calling this microwave-generating tool an oven has long been the source of much confusion. Instead of heating from the outside in, it heats internally. Household electricity converted to high-frequency microwaves excites the moisture and fat molecules in food, and the resulting vibrations create friction that produces heat within the food itself. Therefore, how you cook and what you can cook is quite different in the microwave oven than in a conventional oven.

WHY DO POTATOES COOKED IN A MICROWAVE OVEN TURN GLUEY WHEN MASHED?

The starch in potatoes is held in structures called buds, or granules. When whole, unpeeled potatoes cook in a microwave oven, the water inside them heats rapidly, and when it gets hot enough, the steam that can't escape breaks open the starch buds, releasing their gluey starch.

To avoid this problem, cut peeled potatoes into small cubes and add a little water to cook them, covered, in the microwave oven. The smaller pieces cook faster and more evenly, and the steam escapes without damaging the starch buds.

After cooking potatoes this way, handle them as you would regular boiled potatoes.

WHY DO BROCCOLI FLORETS GET BROWN SPOTS WHEN ZAPPED?

If the broccoli is cooked without any liquid. as you can in the microwave oven, the vegetable takes in oxygen that turns some of its green color brown. If broccoli cooks in water or steam, the moisture drives off the oxygen, and the vegetable stays green. The solution: cook broccoli in a little water in a covered container in the microwave oven.

WHY DOES IT SOMETIMES TAKE LONGER FOR FOOD TO COOK IN A MICROWAVE OVEN?

The rate at which a microwave oven heats food has to do with how much food it is heating. It heats small amounts quickly; increase the volume of food and you increase the amount of time required. If the food is doubled, the time required to heat it may be doubled.

For example, whether you cook one or six artichokes in a pot of simmering water, the cooking time is the same. But if you cook six artichokes in the microwave oven, they may take up to six times as long as a single artichoke.

Big pieces of food - or casseroles for four to six servings - heat differently in the microwave than in a conventional oven. The waves tend to be absorbed before they completely penetrate, so foods are heated unevenly internally. You need to let the food stand briefly after microwaving to give the heat time to equalize. If you microwave longer and skip the standing time, the outside edges of foods (or sometimes the center) will overcook - even scorch - and the internal temperature will still be uneven. In situations like these, a regular oven often works better and faster.

WHY CAN I USE PAPER AND PLASTIC IN THE MICROWAVE OVEN?

The long microwaves simply pass through paper and plastic containers and wrap without heating them. However, once the food is hot, it will transfer heat. If the plastic is designed for microwave use or for cooking, there is no problem. But if the plastic is heat-sensitive, as produce bags and some wrapping materials are, it can melt onto or into the hot food. Avoid these products when you need to get the food really hot.

WHY DO MANUFACTURERS SUGGEST INVERTING A CERAMIC PLATE UNDER A POPCORN BAG IN A 500-WATT (OR LESS) MICROWAVE OVEN?

When the water in the popcorn gets hot, the heat transfers to the plate. The plate holds the heat next to the popcorn and makes more of the kernels pop.