Despite the enduring suspicion that the microwave "zaps" rather than cooks dishes, it remains arguably the best way to retain nutrients, color and flavor in food. Because the microwave cooks by heating the water molecules in food, it is an efficient, fast substitute for stove-top steaming.
Microwaves cook fast but unevenly. They create hot and cool spots that gradually even out while the food stands. Mitigate the temperature disparity by cutting vegetables into equally sized pieces. If cooking broccoli or cauliflower florets, for example, trim away any heavy stalk portions, which take longer to cook than the buds. Arrange the vegetables with the larger pieces around the outside of the dish and the smaller pieces at the center, which contributes to consistent steaming. When arranging florets, place the thicker sections facing outside of the dish.
Put the vegetables in a microwave-proof bowl, ideally plastic, glass or ceramic -- but not metal. A broad, shallow bowl rather than a high-sided dish allows for a single layer of vegetables that will steam evenly. Add a few tablespoonfuls of water for crunchy spring vegetables or as much as ½ cup of water for sturdier ones with a lower water content, such as carrots. Covering the bowl is an essential step to trap the steam caused by heating. A heavy plate can create a sufficiently tight seal, while plastic wrap tends to sag and may allow steam to escape.
Microwave the vegetables on high or full power for three to four minutes, or start off with a 2½ minute blast and check for tenderness. Cook longer if necessary. As The New York Times advises, time can always be added but not taken away. Turn the vegetables during cooking to cook them evenly, but watch for steam when removing the lid. Not all vegetables need to be chopped. Squash and potatos can be steamed whole in the microwave, but pierce them through the skin with a fork before cooking to let the steam escape. While most vegetables emerge with a texture and appearance consistent with conventional steaming, some respond particularly favorably to the microwave. Eggplants, for example, emerge soft and succulent in a fraction of the time it takes on the stove.
Tips and Techniques
Remove the lid carefully from microwaved vegetables, because the steam will escape from the dish. Season foods with salt, pepper and butter right after microwaving -- rather than before -- to allow for maximum absorption. Some vegetables, such as delicate asparagus, do better in a resealable bag instead of a dish and for just a minute or so. The same goes for spinach. In addition, steaming spinach in a microwave keeps its nutrients intact; boiling can result in a loss of 70 percent of its folic acid, according to CNN. As spinach leaves have a tendency to ooze water, there is no need to add water before steaming.