There are a few reasons why some foods may not get hot enough when reheated in a microwave oven:
Inadequate cooking time: Microwave ovens heat food by generating microwaves that excite water molecules within the food, producing heat. If the cooking time is too short, the heat generated may not be enough to thoroughly heat the entire dish, resulting in cold spots.
Uneven distribution of heat: Microwaves may not distribute heat evenly throughout the food. Microwave ovens use a rotating turntable or rotating stirrer to help mitigate this issue, but certain areas of the food may still receive more heat than others. Stirring or rearranging the food halfway through the reheating process can help promote more even heating.
Food composition: The composition and thickness of the food can affect its ability to absorb and retain heat in a microwave. Dense or thick foods, such as large cuts of meat or baked goods, may take longer to heat through compared to smaller or less dense items.
Microwave-safe containers: The type of container used to reheat food can impact the heating process. Microwave-safe containers are designed to withstand the heat generated in a microwave oven and allow the microwaves to penetrate the food effectively. Using non-microwave-safe containers or containers with metal accents can interfere with the microwave's ability to heat the food evenly.
Initial temperature: If the food being reheated is already cold or chilled, it may take longer to reach the desired temperature compared to food that is at room temperature or slightly warm.
To help ensure that food is adequately reheated in a microwave oven, it's recommended to use microwave-safe containers, cover the food to retain moisture, and adjust the cooking time as needed. It can also be helpful to stir or flip the food during the reheating process to promote more even heating.