Gas, Electric and Induction.
A burner's rating says how much power it uses; what matters to the cook is how much reaches the pan, and how fast it changes when you turn the dial.
A domestic gas burner may be rated at 3 kW, but most of its heat goes round the sides of the pan and into the kitchen: only about a third to two-fifths reaches the food. An electric coil delivers about seven-tenths, but its coil must heat up and cool down, so it responds slowly. Induction heats the pan itself through a magnetic field, delivers most of its power, and responds almost at once.
The workshop heats the same empty cast-iron pan on each kind of burner and records how long it takes to reach searing temperature, and how fast it falls when the heat is turned off.
Below: the temperature of a 26 cm cast-iron pan from cold on each burner at full power, and the minutes each needs to reach 200 °C.
- Distinguish a burner's rated power from the power reaching the pan.
- Compare gas, electric coil, glass-ceramic and induction.
- Explain why a wok wants a powerful flame.
- Account for response time when you adjust the heat.
Rated power, delivered power, response
A 3 kW gas burner puts about 1,200 W into the pan and brings an empty 4 mm cast-iron pan to 200 °C in 3.1 minutes; a 2.5 kW induction hob puts in about 2,125 W and takes 1.6; a 2 kW electric coil takes 3.9, the extra coming from the coil's own warming. Delivered power, not the number on the label, sets how fast a pan heats and how much cold food it can take before it stops sizzling.
Response matters as much. Turn a gas flame down and the pan feels it at once; induction is as quick; an electric coil or glass-ceramic hob goes on delivering heat for a minute or more while its element cools — cooks on those hobs often move the pan off the zone to stop cooking quickly. A restaurant wok burner is another animal: 15–25 kW of flame, much of it licking up the wok's sides, which is part of what makes stir-frying in a restaurant different from at home (XV.4–5).
Time how long a litre of cold water takes to boil on each of your burners, with a lid. Delivered power is about 4.19 kJ per litre per degree divided by the time in seconds — 1 litre from 15 to 100 °C is 356 kJ, so a 4-minute boil means about 1.5 kW reached the pot.
Terms
- Rated power
- The power a burner consumes, as marked.
- Efficiency
- The fraction of a burner's power that ends up in the pan.
- Response time
- How quickly the heat reaching the pan follows a change of the knob.
- Induction
- Heating a magnetic pan by eddy currents driven by an alternating magnetic field.
Sources
- A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.