Why Does Induction Burn a Hot Spot in the Middle of the Pan?

The coil is smaller than your pan. On most portable burners it measures about 6 in (15 cm) across, and that is the whole story behind an induction hot spot in the middle of a pan with a pale ring around it: only the metal sitting over that coil is being heated at all. The rest of the base is warmed second-hand, by heat crawling sideways from a disc roughly 6 in (15 cm) wide, and it never catches up while the burner is still pushing power into the centre. Turning the dial down slows both zones by the same proportion, so the ring survives it.

Two numbers decide whether you can fix this without buying a hob: how wide the coil is, and how wide the flat base of your pan is. They are both measurable this afternoon. The Houseland titanium pan is listed at 10.2 in (26 cm) cooking diameter in Small and 11 in (28 cm) in Large for exactly this reason, because the honest answer to "which size" depends on what is under your glass, not on which one sounds more generous.

Why does induction heat a spot in the middle and not the rim?

Heat is not made under the whole pan. It is made in the metal directly above the copper coil, and on a portable unit that coil is small: America's Test Kitchen reports that most models, including the Duxtop it favours, carry a coil about 6 inches in diameter, and warns that the circle printed on the surface marks where to stand the pan rather than the size of the coil underneath. Put a 10 in skillet on that and well under half the base is being cooked directly.

The induced current also sits shallow. Eddy currents concentrate in a thin skin of the base metal, and at 24 kHz that skin is roughly 0.004 in (0.10 mm) deep in carbon steel and 0.02 in (0.56 mm) in aluminium. Field strength drops off fast with distance too, which is why a base that has bellied up in the centre couples worse at the rim than a flat one does.

So the pan is handed a shallow, coil-shaped disc of heat and asked to spread it. Metal does that by conduction, which is slower than the power arriving over the coil. The centre is not faulty and it is not overheating by 50 degrees on its own: it is simply the only part of the base being heated, and it keeps gaining while the outer ring waits. Anything that browns by contact, such as a pancake, a fried egg or a flat layer of onions, reads that gap straight back to you.

How do I find the size of the coil under my own hob?

Dust the cold pan with flour and let the burner draw you a picture.

1. Sift a thin, even layer of plain flour across the dry base, about 1 tablespoon for a 10 in pan. No oil, no food.
2. Run the burner at a middling setting for 3 to 5 minutes and watch, because the flour tans from pale to brown in the order the heat arrives. The brown patch is your coil, drawn at full scale.
3. Tip the flour out and measure the browned disc with a ruler, to the nearest half inch. That figure, not the printed circle, is the working width you have.
4. Now measure the flat base of the pan, not the rim. Cooktop Hunter makes the point that pans flare, so a skillet sold as 10 inch may have a flat base of only 8 inches.
5. Subtract one from the other and you have the width of your pale ring. Two inches of overhang all round is a ring you will taste; half an inch is one you will not.

Do it on a built-in hob as well as a portable one. Built-in zones are usually wider, but the small front-left zone that came free with the kitchen is often the one you reach for on a weeknight, and it can be narrower than the portable unit in the cupboard.

Which pan size actually suits the zone you have?

Match the flat base to the coil, then allow about an inch of overhang and no more. The published minimums are all about detection rather than even cooking, so they set the floor, not the target.

Read the third column twice if you were about to buy bigger. Overhang does not gain you power; it only adds base for the same coil to warm. That is the reasoning behind our own two widths: the Houseland pan in Small is 10.2 in (26 cm) cooking diameter and the Large is 11 in (28 cm), and over a portable burner the Small is the one to take, while the Large earns its keep on a full-size zone where the coil can back it up. We put the rest of the buying checks in what to check before buying any pan for induction, and base flatness is top of that list.

From the shop

Titanium Frying Pan, Uncoated, Induction Safe, with Tempered Glass Lid

Uncoated titanium cooking surface with a hammered finish and no PTFE, PFOA or PFAS on it, in a 10.2 in (26 cm) Small or an 11 in (28 cm) Large, each with a lid sized to the pan. Works on induction, gas, electric and ceramic; hand wash, wood or silicone utensils.

View the uncoated titanium pan — 2 sizes & current price

Why doesn't turning the power down fix the pale ring?

Power decides how fast the centre gains, not where the heat lands. Halve the setting and the coil still heats the same disc, the rim still waits on conduction, and the gap between them narrows only as much as the slower pace allows. What actually closes the gap is time and mass: minutes of conduction before the food goes in, and enough metal in the base to hold what it has spread.

America's Test Kitchen's own advice runs the same way. Preheat with oil in the pan a few minutes longer than usual so heat can even out before food touches it, and lift the pan partly off the burner for a few seconds to swirl the oil around rather than reaching for more power. Both work because they move heat sideways, which is the thing the coil cannot do for you.

There is a second trap on cheap units. Many hold a low setting by pulsing full power on and off instead of heating gently, and you can hear it: a click or a change in fan note every few seconds. If yours pulses, "low" is really "full power one second in four", and the centre still gets full-power bursts. Cook on a lower setting with the lid on instead, so trapped steam heats the food the coil is not reaching.

Coil size is genuinely what the money buys, by the way. The same test kitchen notes that the Breville and PolyScience Control Freak has a much larger coil and costs about $1,500, against roughly $120 for the budget units most kitchens own. Technique is the cheaper half of that difference.

What changes should you make to how you cook on it?

Move the food and the pan, and stop trying to cook the full width of a base the coil never reaches.

• Cook to the coil, not to the pan: one pancake in the middle beats three arranged in a ring. Batch size is the fastest fix on this whole list.
• Rotate the pan a half turn every 60 to 90 seconds when you are searing. It averages out the off-centre browning without touching the food.
• Give the pan 4 to 5 minutes of preheat with a little fat before food arrives, rather than 1 minute. Conduction needs that time and gets it back in even colour.
• Start onions or mushrooms piled over the centre, then push them outwards as they soften. The outer zone finishes food; the centre starts it.
• Use the lid for anything with moisture in it, since steam heats the ring the coil misses. A pale ring on a covered pan is a much smaller problem.
• Add liquid to a hot centre before it turns to carbon, then deglaze while the pan is still warm. That is the difference between a fond you can use and a scrub.

Preheat is worth learning properly rather than guessing, and the water-bead trick tells you when the metal is ready: we wrote it up in how to preheat with the water test. If the centre has already gone dark and hard on you a few times, getting burnt food off a hammered pan is a soak job, not a scouring job, and the finish survives it.

What I'd do

Run the flour test first, then buy nothing until you have the two numbers. Nine times out of ten the coil turns out to be around 6 in (15 cm), the pan on top of it has a flat base of 9 or 10 in, and the answer is a smaller pan plus a longer preheat rather than a new hob.

If you are replacing the pan anyway, size it to the zone you actually cook on. Our Houseland titanium pan is sold in 10.2 in (26 cm) and 11 in (28 cm) cooking diameters, both uncoated with no PTFE, PFOA or PFAS on the cooking surface, both supplied with a lid sized to the pan, and both happy on induction, gas, electric or ceramic. Hand wash, deglaze while warm, wood or silicone utensils. Take the 10.2 in (26 cm) Small if a portable burner is your main hob, and the 11 in (28 cm) Large only if the zone underneath can feed it. The rest of the range sits in kitchen and home, and the same coil arithmetic decides every one of them.

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