Induction hob query

[Wowbagger]

This is science. So beware. It's almost like an O level question...

Most mornings I cook porridge on an induction hob. I have two different styles saucepan that I use (both bought in Waitrose, naturally...) and I get different results. I heat the porridge on a 3.5 level until it is boiling, then I reduce the heat to a 1 until it is the consistency I like. With my preferred saucepan, reducing the temperature in this way ensures that the porridge never sticks to the bottom of the pan. When I use the other pan, even when the heat is reduced to 1, the porridge sticks, which to me implies a higher temperature. The latter pan has a smaller diameter than my preferred pan but also a thicker base. I think that it also is slightly more sensitive to a fridge magnet, but I'm not absolutely certain about this.

If it were more sensitive to magnetism, would that lead to a higher temperature for the same amount of energy consumed?

[Von Broad]

thicker base

Coming to mind first without a lot of thought, it might be that the thicker base is retaining more heat for longer before it drops down to 1, and in so doing causing the porridge to stick, whereas your preferred pan with a thinner base cools quicker.......maybe!

[sizbut]

Ditto, thicker base, stays hotter for longer once its heated.

[Feanor]

It's not really an Induction Hob specific thing, I think.

Different pans exhibit different thermal properties. Same across all hobs.

[Wowbagger]

I'm not convinced by the thicker base argument.

Sometimes I leave the porridge on a 3.5 for slightly longer than I should and the porridge sticks. In the favoured pan, I can then turn it down to a 1 and the "stuck" porridge absorbs moisture from the rest of the pan and stirring it will remove all the stuck porridge from the base. This is not the case with the other pan. This morning when I turned the heat down to a 1 and stirred it, there was no stuck porridge. 10 minutes later, there was.

[lissotriton]

Some hobs can have hotspots. So it burns in some parts, but not other. Though a thicker base should help, by spreading the heat more evenly.
And could depend on the size of the pan relative to the hob, and exactly where it is positioned.

And what sort of spurtle are you using?

[Mrs Pingu]

I'm not convinced by the thicker base argument.

Sometimes I leave the porridge on a 3.5 for slightly longer than I should and the porridge sticks. In the favoured pan, I can then turn it down to a 1 and the "stuck" porridge absorbs moisture from the rest of the pan and stirring it will remove all the stuck porridge from the base. This is not the case with the other pan. This morning when I turned the heat down to a 1 and stirred it, there was no stuck porridge. 10 minutes later, there was.

Yebbut 10 mins later (which sounds like a really long time after boiling to me) the base of the small diameter thicker base pan will be a lot hotter than the thinner pan. There's no way I'd be leaving porridge unstirred 10mins after it had reached boiling in one of my cast iron pans.

You also don't mention if the material of the pan or inner coating is different.

[nicknack]

Get a decent non-stick pan. The modern ones are brilliant.

[Wowbagger]

The inners are uncoated stainless steel. Never have a problem with stuff "sticking". The porridge is easy to get off - just soak in cold water.

[rafletcher]

It’ll be a different construction if the base. We have some decades old, very expensive then, Polaris pans that heat quickly. Copper sandwich base. We have a modern non-stick thinner based not very expensive pan that takes a long time to heat.

[aidan.f]

The copper won't itself heat, but it's going to moderate the heated steel . There are some high quality stainless steels that don't heat, It's all about how much energy is lost while flipping the magnetism about. (hysteresis loss), Mrs H. got the thin base of our coffee pot hot enough to burn a chopping board, . Induction hob drivers do quite complex adaption of frequency waveform and phase to couple energy into a variable load ... Big pan, little pan, move the pan

[Diver300]

The copper won't itself heat, but it's going to moderate the heated steel . There are some high quality stainless steels that don't heat, It's all about how much energy is lost while flipping the magnetism about. (hysteresis loss), Mrs H. got the thin base of our coffee pot hot enough to burn a chopping board, . Induction hob drivers do quite complex adaption of frequency waveform and phase to couple energy into a variable load ... Big pan, little pan, move the pan

Most of the heating comes from the currents circulating in the metal of the pan (eddy currents). Obviously the magnetic properties of the pan affect the strength of the magnetic field, which in turn affects how much current flows, but it's the current that does the heating. A lot of aluminium pans are made to work on an induction cooker have a steel insert cast into the bottom of them to help with the magnetic field.

I don't think that hysteresis loss contributes much to the heating. Wikipedia says <10%. https://en.wikipedia.org/wiki/Induction_cooking

Transformer cores are either laminated so that they don't conduct in certain directions, or made out of bits of magnetic material glued together, so that they don't conduct. That wouldn't be necessary if eddy-current heating were very small. Pans, on the other hand, do conduct so they get hot.

[aidan.f]

D300 Thanks for correction and clarification.

[TimC]

I find that some of my pans - woks are worst - have distorted bases that mean they don't heat consistently on my induction hob. 

[Diver300]

I find that some of my pans - woks are worst - have distorted bases that mean they don't heat consistently on my induction hob.

Our induction hob has a single gas burner* with an optional wok holder, which we assume is because induction hobs aren't good with woks.

*It hasn't worked for some years and is currently disconnected from the gas, but the 4 induction rings are fine.

[fruitcake]

I reckon if I used a milk pan or a wok (thin bases) porridge would stick. So I'd choose the cast iron enamel coated one and use the induction on the lowest heat.

[Cudzoziemiec]

The history section of the Wikipedia page linked to upthread is interesting. Turns out induction cooking is approximately as old as electric cars...

[Wowbagger]

I find that some of my pans - woks are worst - have distorted bases that mean they don't heat consistently on my induction hob.

I find that flat-bottomed pans make the wokking world go round.

[Mr Larrington]

Good heavens!  Was that ^^^^ a Popular Beat reference?

[Pedal Castro]

The history section of the Wikipedia page linked to upthread is interesting. Turns out induction cooking is approximately as old as electric cars...

"more than a century ago" according to a question on induction hobs in the International A level paper I'm currently marking.

[T42]

I find that some of my pans - woks are worst - have distorted bases that mean they don't heat consistently on my induction hob.

I find that flat-bottomed pans make the wokking world go round.

Well played, sir!

[Diver300]

The history section of the Wikipedia page linked to upthread is interesting. Turns out induction cooking is approximately as old as electric cars...

Bearing heaters have been a form of induction heater for a very long time. The early ones used mains-frequency electricity, and were really a transformer with the bearing as the secondary. The core of the transformer was made so that it could easily be taken apart and assembled through the centre of a bearing to form a complete ring of magnetic material.

Modern ones use much higher frequencies, like induction hobs, and they don't need a complete ring for the magnetic field.

Other interesting fact. Induction heaters and wireless chargers use Litz wire (https://en.wikipedia.org/wiki/Litz_wire) which is only of any use for high-power, high-frequency devices. Until the electronics to make high-power, high-frequency power became cheap, Litz wire was only used in really niche applications, like radio transmitters.

[Cudzoziemiec]

The history section of the Wikipedia page linked to upthread is interesting. Turns out induction cooking is approximately as old as electric cars...

"more than a century ago" according to a question on induction hobs in the International A level paper I'm currently marking.

for example see UK Patent Application GB190612333, entitled "Improvements in or relating to Apparatus for the Electrical Production of Heat for Cooking and other purposes", applied for by Arthur F. Berry on 26 May 1906

according to the refs on Wikipedia.

[FifeingEejit]

I remember Home Eck classes mentioning magnetic induction and special pans.
I never came across such magical devices until I found one at the Kershader hostel, which indeed did have special pans that slotted together with the hob.