Steel teapots?

[KapnoPhilia88]

Do you see any advantages of a porcelain pot over a steel one?

[Youzi]

Steel would be twice as easy to heat up, so you could reach much higher brewing temperatures, and have a stronger extraction.

[debunix]

Depends on your goals. For least worry about breakage during prepration and cleanup, steel would be better; for quality of tea prepared, doubt there is much difference; for aesthetic pleasure--and this is an important part of what brings me back to tea again and again--the brewing vessel is a great excuse to peruse, purchase, and enjoy fine ceramics. But for lightest weight and least-stress brewing on the road, I bring the plastic Kamjove device.

[KapnoPhilia88]

Thank you for commenting, I will try a Frieling 34 oz. Stainless pot with basket. This is about the volume of a thermos, so I hope it works well both travel and home brewing.

[pedant]

Steel would be twice as easy to heat up, so you could reach much higher brewing temperatures, and have a stronger extraction.

i disagree with your reasoning. my thinking is:

the thermal conductivity of stainless steel is nearly 10x that of porcelain (14.4W⋅m^-1⋅K^-1 vs 1.5W⋅m^-1⋅K^-1), so the environment will pull heat out of your brew much faster. this drops temperature faster and makes it harder to extract.

[Youzi]

Steel would be twice as easy to heat up, so you could reach much higher brewing temperatures, and have a stronger extraction.

i disagree with your reasoning. my thinking is:

the thermal conductivity of stainless steel is nearly 10x that of porcelain (14.4W⋅m^-1⋅K^-1 vs 1.5W⋅m^-1⋅K^-1), so the environment will pull heat out of your brew much faster. this drops temperature faster and makes it harder to extract.

The teapot cools by convection though. Wouldn't it rather mean, that the heatloss on the outside would appear on the inside faster, while with clay there is basically a "delay".
Ofc the material of the surface which you keep your teapot on would matter much more in the case of metals, so you should insulate that, but I think you'd win much more on the peak temperature than what you lose on conductivity, if you can insulate the bottom.

[faj]

I think you'd win much more on the peak temperature than what you lose on conductivity, if you can insulate the bottom.

Can you explain your thinking about how, and in which cases, a metal teapot would allow a higher peak temperature?

[Youzi]

I think you'd win much more on the peak temperature than what you lose on conductivity, if you can insulate the bottom.

Can you explain your thinking about how, and in which cases, a metal teapot would allow a higher peak temperature?

Easier to heat up, due to lower heat capacity.

[faj]

Easier to heat up, due to lower heat capacity.

A couple of thoughts...

A quick Google search leads me to some random website stating the specific heat of steel is half that of porcelain. So you are right the heat capacity is lower. Will that lead to a higher peak temperature? I am not sure.

• If the vessel is preheated to a temperature close to that of the water, its capacity to absorb heat is almost saturated, and matters very little.
• Heat capacity depends on mass. If a steel vessel is twice the weight, then the absolute heat capacity is the same. In other words, for the lower heat capacity to help, the steel vessel has to be thinner, because metal is much more dense than porcelain or clay.
• Insulation properties may dominate heat capacity irrespective of the above. I would hazard a guess that in addition to better conductivity, metal also radiates heat more efficiently.

Depending on the relative speed of both processes (heat transfer from water to teapot, and heat transfer from teapot to the environment), many scenarios are possible when starting with non-preheated vessels. It is quite possible that the slower heat transfer of clay/porcelain yields higher initial temperatures, then later on lower temperatures once the material has been fully heated, and later on again higher temperature because insulation becomes the main factor.

[pedant]

@Youzi, any way you look at it, having a more conductive vessel transfers heat from the liquid to the environment faster.

all of these are in series with the conduction through the teapot material:

• convection (or conduction depending on how much leaf is packed in there) from the teapot's contents into the teapot
• conduction from the teapot into the surface below
• convection from the teapot to the surrounding air
• radiation from the teapot to the environment

and for radiative cooling, a metal teapot will have a higher emissivity than a ceramic one.

[pedant]

Depending on the relative speed of both processes (heat transfer from water to teapot, and heat transfer from teapot to the environment), many scenarios are possible

yes. there are all kinds of edge cases. we'd need to play around with CFD models or measure real tea session temperatures.

and though i am pretty much intuitively convinced that a ceramic teapot of ordinary thickness is going to give better thermal performance in ordinary brewing conditions, i don't think i'll ever own a <150mL steel teapot though, so for me, this is kind of moot.

and i think it's clear that the larger you go in vessel volume, the more the vessel conductivity dominates due to decreasing surface-area-to-volume ratio (and therefore decreasing teapot-to-contents mass ratio).

[faj]

yes. there are all kinds of edge cases. we'd need to play around with CFD models or measure real tea session temperatures.

I hope, at some point, to get some kind of temperature probe that can be connected to a computer for simple temperature recording. That will not give me better tea, but it would scratch an itch and provide a bit of data to complement intuitions. Discussions about temperature tend to come up on a regular basis, and in the end we have little data to go by.

[Youzi]

yes. there are all kinds of edge cases. we'd need to play around with CFD models or measure real tea session temperatures.

I hope, at some point, to get some kind of temperature probe that can be connected to a computer for simple temperature recording. That will not give me better tea, but it would scratch an itch and provide a bit of data to complement intuitions. Discussions about temperature tend to come up on a regular basis, and in the end we have little data to go by.

Get an IR temp camera.

[faj]

Get an IR temp camera.

I have an IR probe at home, and in my tests its readings for the temperature of water were way off. It seems to measure the temperature of the teapot wall at the bottom of the vessel, the water itself seems transparent to infrared, as it is with visible light. A kitchen probe thermometer easily shows the difference to be surprisingly high (10C-15C for a smallish teapot).

Besides, I am lazy, I would rather have software do the logging to show the curve without any manual work. Also, being lazy, so I have not gotten a probe to do that yet, and maybe I never will...

[Youzi]

Get an IR temp camera.

I have an IR probe at home, and in my tests its readings for the temperature of water were way off. It seems to measure the temperature of the teapot wall at the bottom of the vessel, the water itself seems transparent to infrared, as it is with visible light. A kitchen probe thermometer easily shows the difference to be surprisingly high (10C-15C for a smallish teapot).

Besides, I am lazy, I would rather have software do the logging to show the curve without any manual work. Also, being lazy, so I have not gotten a probe to do that yet, and maybe I never will...

yes, it's more accurate to measure the outer temperature of the teapot if you want to be consistent. that'll give you a min reading for the overall brewing temp. based on my tests it's about 2-3 degree lower than the average temperature of the brewing water.

The bigger your teapot is the more inaccurate of both a probe and outer IR measurements become. I've only tested 50-140ml teapots so far though. So for those using outside IR measurements is much better, due to the added consistency for your readings.

(don't measure temp through water with an IR gun, it's too inaccurate for anything) Also, make sure the adjust the Emissivity of the IR gun for the matter you are trying to measure.