Covering keeps moisture in the food from evaporating too rapidly, thus helping the microwaves cook more evenly. Plastic wraps are routinely recommended for covering food in the microwave, particularly when abundant steam is needed for tenderizing and speeding the cooking along. But higher temperatures and prolonged contact with foodespecially foods with high fat and sugar contentΓÇöincrease chances that the plastic will melt. When plastic wrap is called for, always provide an inch or more of space between the food and the wrap. And only microwave with plastic wraps that are clearly labeled safe for the microwave; ones not labeled as such may contain many plasticizers, which cause the plastic to melt quickly and possibly transfer unwanted chemicals to the food. Because of the buildup of steam, never tightly seal a dish with plastic wrap. If a recipe directs you to cover tightly during cooking, use a microwave-safe lid. If using plastic wrap, give the steam a way out: fold back an edge about an inch. When removing a lid or wrap, lift it from the side away from you to avoid the escaping steam, which can easily scald you. When neither trapping steam nor absorbing moisture is your goal (say, when microwaving a plate of leftovers), lay a sheet of wax paper on top of the dish. Paper towels and napkins are good for covering foods that splatter, such as melting butter.
