The Middle Warms by Conduction

The middle warms as heat spreads in

The middle warms up as heat from the surface slowly spreads inward. The color of the cut face shows temperature. Heat food from the fridge for 2 minutes and the surface reaches 50 °C, but the middle is only 34 °C. Turn it off and wait one minute, and the heat spreads in, raising the middle to 35 °C. That is why recipes say “let stand for a minute.”

Why?Leave a spoon in hot soup and the handle slowly gets hot too. Particles on the hot side jostle their neighbors and pass the heat along. Inside food, heat moves inward one layer at a time, and it moves slowly, so it takes a few minutes.

Learn moreHeat moving through a material like this is called conduction. This calculation assumes food at 5 °C, 4 cm thick, receiving about 600 W per half kilogram. It follows the heat made near the surface and the heat spreading inward, one second at a time.

After 2 minutes (calculated)

Middle 34 °C

textbook formulas · example oven cavity 31.5 × 21 × 32.5 cm