The uneven nature of microwave cooking can make it a dangerous way to prepare frozen raw foods. When not all of the food is heated to a safe temperature, pockets of bacteria can survive.
U.S. Department of Agriculture food safety experts offer several tips for preventing that.
Microwave cooking instructions are based on particular wattages, or power. Food takes longer to cook safely in a microwave with lower wattage.
But checking your user manual for the wattage may not be enough. A microwave's actual output can differ, and it can deteriorate over time.
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To test your microwave, place several ice cubes in water, stir to make sure the water is ice cold and then remove any remaining ice and discard. Measure 1 cup of the chilled water and set it in the microwave. Heat on high for 4 minutes, watching to see when the water boils. If the water boils in less than two minutes, the oven has at least 1,000 watts.
If water boils in 2 1/2 minutes, the microwave produces about 800 watts. If water boils in 3 minutes or longer, it is producing 700 watts or less.
Food safety experts recommend using an instant-read food thermometer to check the final temperature.
If the cooking instructions call for letting the food sit after cooking, wait until after that before taking the temperature, to allow the heat to spread.