By Harold McGee
Microwave radiation selectively energizes the water molecules in fruits and vegetables, and the water molecules then heat up the cell wall, starch, and other plant molecules. Because radiation penetrates into food an inch/2 cm or so, it can be a fairly rapid method, and is an excellent one for retaining vitamins and minerals. However, it has several quirks that the cook must anticipate and compensate for. Because the microwaves penetrate a limited distance into the food, they will cook evenly only if the food is cut into similar-sized thin pieces, and the pieces arranged in a single layer or very loose pile. Energetic water molecules turn into water vapor and escape from the food: so microwaves tend to dry foods out. Vegetables should be enclosed in an almost steam-tight container, and often benefit from starting out with a small amount of added water so that their surfaces don’t lose too much moisture and shrivel. And because the foods must be enclosed, they retain some volatile chemicals that would otherwise escape—so their flavor can seem strong and odd. The inclusion of other aromatics can help mask this effect.