What Does Auto Defrost on a Microwave Do?

The auto defrost feature on a microwave oven thaws frozen food to cook in the microwave or by other methods. The microwave defrosts food much faster than by letting it thaw naturally in the refrigerator. Auto defrost also offers the convenience of not having to change many settings.

A microwave oven with an auto-defrost setting.

How it Works

By using the auto-defrost function on a microwave, the user does not have to manually lower the power level or calculate the time. Instead, based on the weight entered by the user, the oven will automatically make those adjustments. A microwave oven defrosts by using bursts of low heat. In between bouts of heat, the warm portions of the food transfer heat to the colder parts, allowing for more even thawing.


Some types of auto defrost only prompt the user to input the weight of the item. The oven then calculates the appropriate power level and length of time. Other varieties also require the user to select the type of food to defrost — for instance, meat, fish or poultry. These ovens make more specific adjustments to the power and time to accommodate the particular type of food.


Unwrap the item and place it on a microwave-safe plate in the center of the oven's pedestal. Select the auto-defrost feature. If prompted, choose the type of food (meat, fish or poultry). Then, input the weight of the item and select the start button. A countdown timer will appear on the display to show how long the auto defrost cycle will take.


Always cook food immediately after defrosting to avoid foodborne illness. Bacteria multiplies rapidly in the temperature "danger zone" of between 40 and 140 degrees Fahrenheit. After defrosting, the temperature of the food may lie in the danger zone, and so should be used promptly.