Vol. II · Heat Plate 5 of 11pans, copper, aluminium, cast iron, stainless steel, clad, hot spots, heat capacityHT

Pans and Their Metals.

A pan has two jobs: spread the burner's heat across its base, and hold enough heat that food going in does not chill it. Different metals are good at different jobs.

A gas flame or an induction coil heats only part of a pan's base. Whether the rest of the base keeps up depends on how well the metal carries heat sideways — its conductivity times its thickness. A thin stainless-steel pan develops a ring of scorching just above the flame and cooler edges; a thick aluminium or copper base evens it out. That is why good stainless pans are clad, with a core of aluminium or copper sandwiched in steel.

The second job is storage. A heavy cast-iron pan holds a lot of heat, so a steak laid in it barely dents its temperature (XV.3), but it is slow to heat and slow to respond. The workshop shows both: the temperature across the base of a loaded pan over a burner, and how much heat each pan stores.

Below: steady temperature from the centre to the rim of a 26 cm pan base of the metal and thickness you choose, over a burner 16 cm across, with food on it; and the spread from hottest to coolest for every metal at the same thickness.

What you will learn
Workshop
Steady temperature across the base, centre to rim, with 800 W entering over a 16 cm circle and food above drawing heat at 300 W/m² K from 60 °C (a fin model solved on the stove bench). Right: hottest minus coolest for each metal at the chosen thickness.

Spreading and storing

At 3 mm, a stainless-steel base runs 130 °C hotter over the flame than at its rim; aluminium 62 °C and copper 40 °C. The difference is conductivity: stainless steel conducts about 16 W/m K, aluminium about 205 and copper about 390, so heat spreads sideways a few centimetres in aluminium and copper but barely one in steel. Thickness helps every metal — a thick base carries more heat sideways — which is why cheap thin pans scorch in a ring and why clad pans put aluminium or copper in the middle of the steel.

Storage is mass times specific heat. A 5 mm cast-iron base stores about 1.19 kJ for each degree of its temperature, a 3 mm aluminium one 0.52 kJ: when 300 g of cold steak goes in, the iron pan loses fewer degrees and recovers its sear sooner. But the iron also takes longer to heat and to cool when you turn the flame down. Hence the cook's choices: heavy iron or carbon steel to sear; clad stainless or aluminium for sauces and even sautéing; thin carbon steel for a wok, which must respond in seconds; non-stick aluminium for eggs, kept below about 250 °C.

At the stove

Sprinkle a thin, even layer of flour over the base of a dry pan and heat it on a medium burner. Watch where it browns first. On a thin pan you will see a ring above the flame; on a heavy or clad pan the browning is more even. Wash the pan afterwards.

Copper pans have been prized by French chefs for centuries for their evenness, but bare copper reacts with acidic food, so they are lined with tin or, now usually, stainless steel.

Terms

Hot spot
Part of a pan's base much hotter than the rest, usually over the flame or coil.
Clad pan
A pan whose base or body is layers of metal, usually aluminium or copper inside stainless steel.
Heat capacity of a pan
The heat it stores per degree: mass times specific heat.
Spreading length
How far heat travels sideways in a pan base before it is drawn into the food; grows with conductivity and thickness.
A pan spreads heat (conductivity × thickness: copper, aluminium) and stores heat (mass × specific heat: cast iron). Choose for the job.

Sources

  1. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.