Why the middle of a big pot stays warm
Heat does not leave a pot all at once. It moves from the hot center toward cooler surfaces, then escapes into the surrounding air. In a deep, densely packed pot, the center is far from those surfaces, and the food itself slows the movement of heat. The outside may feel cool while the middle remains warm for much longer.
That matters because many bacteria grow more readily in warm food than in cold food. Leaving a large pot on the counter gives its center extra time in conditions where microbes can multiply; the food can become riskier even if it still looks and smells normal.
Smaller portions shorten the wait
Dividing leftovers into shallow containers changes the geometry. Heat has a shorter distance to travel from the center to the surface, and more of the food is exposed to cooler surroundings. The refrigerator can then pull heat away more effectively, bringing the food down to a temperature that slows bacterial growth.
The practical point is not to wait until a whole pot reaches room temperature before refrigerating it. Portioning it promptly is a better way to cool it. Keep containers shallow rather than stacking a deep mass of food, and leave space around them so cold air can circulate. Refrigeration does not undo bacterial growth that has already happened, so faster cooling preserves a safer window for eating the leftovers.
