Here’s the thing about microwaves that most people don’t know: they don’t heat food evenly. The shape of your food, how thick it is, and how dense it is all affect how the heat moves through it. Some spots get blasted with heat while others barely warm up at all. Those cooler areas are called cold spots.
Cold spots are a real problem because bacteria can survive in them. Food safety experts call the temperature range where harmful bacteria can survive the ‘Danger Zone.’ In a cold spot, the food may never get hot enough to leave that zone — meaning pathogens like Listeria and E. coli can still be alive in your food even when the outside feels piping hot.
The fix is actually pretty simple. A lot of food packages tell you to let your food sit for a few minutes after microwaving — don’t skip that step. That resting time lets the heat redistribute and even out through the food. Stirring partway through cooking also helps break up cold spots. And if you’re reheating something dense or thick, give it extra time. The USDA recommends leftovers reach an internal temperature of 165°F (74°C) — a food thermometer is the only way to know for sure.
The single most important thing to remember: hot on the outside doesn’t mean safe all the way through. Let it rest, stir when you can, and don’t rush it.