Reheating food in a microwave often results in an uneven temperatures throughout your food. To avoid this problem, you need to locate the hot spots in your microwave and place your food accordingly. Wired Magazine has discovered you can do this easily by nuking a plate of marshmallows.
Photo remixed from originals by John Morgan and Wired.
The marshmallows serve as useful heat beacons:
Cook a tray of marshmallows in your oven. In the hot spots, "the marshmallows puff up and melt, and in the cold spots the marshmallows don't change much," says Lou Bloomfield, professor of physics at the University of Virginia. If there are too many hot spots, your best strategy is to keep your food moving, which is why most microwaves have turntables (one study showed these can increase the temperature uniformity by 40 per cent).
It's actually been years since I've seen even a cheapo microwave without a turntable, but if you do have one, this could be helpful. As previously noted, the edge of the microwave is almost always your best bet for even heating.
Microwave Food Evenly [Wired]