Three Ways Heat Gets In

Toast comes out crisp and brown on its faces and soft in the middle. A roast potato is crunchy outside and fluffy inside. A bowl of soup from the microwave can scald at the rim and still be cold in the centre. Each method has left its own fingerprint, because each one delivers heat to the food in a different way.

There are three ways in: through contact with something hot (conduction), carried by moving liquid or air (convection), and as radiation from a glowing element or a microwave. Most cooking uses more than one at once. All three deliver heat to the surface first, which is why the centre always cooks last.