Heat transfer explains most of the instructions in a recipe

This looks at how heat cooks food from the practical end — what holds up once conditions stop being ideal.

Three ways heat arrives

Conduction is contact: a pan touching a steak, or heat travelling inward through the meat itself. Convection is a moving fluid carrying heat, whether that is air in a fan oven, water in a pot or oil in a fryer.

Radiation is heat travelling as infrared, which is what a grill element and glowing charcoal are doing. Most cooking uses two or three at once, and knowing which one dominates tells you what to change when something goes wrong.

Why water sets a ceiling

While liquid water is present at the surface it holds the temperature near its boiling point, because the energy goes into evaporation. Browning reactions need a good deal more than that, which is why nothing boiled, steamed or poached ever browns. It also explains why a wet surface must dry before a sear starts, and why a lid prevents crisping.

The corollary is useful: anything you want brown must be dry, and anything you want gently cooked can be kept wet on purpose.

Air is slower than it looks

An oven at a given temperature cooks far more gently than a pan at the same temperature because air conducts heat poorly. You can hold a hand in a hot oven for a moment and not in boiling water at a much lower temperature. A fan speeds this up by removing the insulating boundary layer of still air around the food, which is why fan recipes reduce the temperature.

Nine times out of ten, it is also why a preheated metal tray browns the underside of a pizza that hot air alone cannot.

Mass, contact and recovery

A heavy pan stores energy and gives it up to the food quickly, keeping the surface temperature high when cold food arrives. A thin pan cannot, which is the mechanism behind most crowded-pan failures. Good contact matters too: a flat pan on a flat hob transfers far more than a warped one that touches in three places.

This is also why food should be pressed into contact briefly rather than moved around for the first minute of a sear.

Heat has to travel inward

Once heat reaches the surface it still has to conduct to the centre, and food conducts heat poorly. That lag is why a thick piece can be burnt outside and raw inside, and why lower heat for longer fixes it.

On a weeknight, bone, fat and air pockets all conduct at different rates, which is why a bone-in joint cooks unevenly around the bone. Letting cold food sit out briefly reduces the gradient a little, though the effect is smaller than commonly claimed.

Using the model to troubleshoot

Burnt outside and raw inside means too much heat at the surface: lower the temperature or move the food further from the source. Pale and wet means the surface never got hot enough: dry it, use less food at once, or use a heavier pan. Cooked unevenly means the heat is arriving from one side only: turn it, use a rack, or move to an oven.

If you are short of time, almost every fault has a heat-transfer answer, which is more useful than a list of remedies to memorise.

The takeaway

Ask what is carrying the heat and whether the surface is wet. Most cooking problems answer themselves.

Taste it before it leaves the pan. That is most of cooking.