Why Is Resting Time Needed After Microwaving?

Microwaves penetrate a few centimeters into food, where most of the heat is generated; heat then reaches the center by conduction, moving from layer to layer. This process continues after the appliance stops. That is why the edges of a dish fresh from the microwave can be scorching hot while the center is lukewarm; a few minutes later, the temperature in the same dish is noticeably more even. Resting is not idle time; it is a continuing part of cooking. When the oven shuts off, heat is still moving through the food.

Resting is also a safety step. When leftovers are reheated, every part needs to get hot enough; a cold spot in microwaved food can allow bacteria to survive. After heating, stir the food and let it rest for 1 to 2 minutes to eliminate cold spots. Thick portions and whole pieces need more time. Use a thermometer to check whether the thickest part has reached 74°C / 165°F. Stirring helps the temperature even out noticeably faster. Testing by touch cannot show whether food has reached 74°C / 165°F; check it with a thermometer in several places.

Resting time can also be part of a recipe. Vegetables cooked in the microwave continue cooking in their own steam while they rest, so turn off the appliance before they reach the desired tenderness. Remove butter and chocolate while they are half melted, then stir to melt the rest. In mixtures containing eggs, resting helps prevent them from overcurdling. For starchy foods such as rice and pasta, resting allows moisture to distribute evenly among the grains. That is why the resting time in a recipe is part of the step, not just a suggestion.

Keep the container covered while the food rests. A microwave-safe lid or paper towel holds in steam and helps the heat even out; do not seal the lid completely, so steam can escape. You can leave the container inside the oven or take it out and let it rest on the counter. The container itself may be very hot when removed; even though the food is what heated up, it transfers heat to the container, so you may need an oven mitt. Let the food rest in its container with the lid on.

If you skip resting, two results can follow. First, the center of the food stays cold, and you may not notice until the first bite; if you heat it a second time, the edges can dry out. Second, unevenly heated food can burn your mouth; filled pastries, especially those with jam or cheese, can be boiling hot inside even when the outside is lukewarm. Do not heat baby food or a baby bottle in the microwave; the risk of uneven heating is especially high for these items. If the food is heated unevenly, stir it and microwave it for one more short interval.