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Cookware Even Heating Testing Methodologies

COOKWARE EVEN HEATING TESTING METHODOLOGY

I went through several iterations of testing methodologies before settling on two that I thought were realistic and representative of how people use their cookware. I’m also planning on a couple of upgrades and additions to these tests that I thought up on my own, but if you have suggestions on cookware to test or how to make testing methodology even better, let me know.

OLD Electric (Induction, Coil, Radiant, Halogen) Testing

Diagram of Pan Bottom (Point B = 400 degrees F <sup class='footnote'><figcaption id=1)” width=”280″ height=”280″ /> Diagram of Pan Bottom (Point B = 350 degrees F 2)
I heated all the cookware one at a time with a Cooktek MC1800 induction cooker at ~790 watt power (power setting usually about 10 of 20, varying based on the cookware), which is equal to ~5,900 Btu/h[1], which is equal to medium heat on a typical residential natural gas range. I allowed for complete cooldown to room temperature each time for both the cooktop and cookware. Throughout this entire process, I recorded data with a professional forward looking infrared thermal imaging camera and a professional dual-thermocouple thermometer. I then went back over my recorded data to find the moment in time when the center of the pan hit 350 degrees Fahrenheit (point B on the diagram). Then I took the average of points A and C and subtracted it from the temperature at point B. I did this for each piece of cookware. There are some other factors I had to correct for, like emissivity and ambient reflections and temperatures, hence the Fieldpiece thermometer for verification. I took several temperature readings per cookware heating cycle to ensure consistency.

Bottom Line: the lower the temperature delta (difference), the better, and ideally cookware would have a 10 cm temperature delta of zero. That is, ideally the entire cookware surface should be the same temperature.

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Show 2 footnotes

  1. 44 degrees C ↩
  2. 7 degrees C ↩

Cookware Even Heating Rankings (Butane, Propane, Natural Gas, etc.)

Lodge Carbon Steel on Gas Burner (heated above 350F for better contrast)
Lodge Carbon Steel on Gas Burner (heated above 350F for better contrast)

For electric coil/induction/radiant/halogen rankings, please see Even Heating Rankings (Induction and Electric). For more details on testing methodology, see here.

EVERY COMPANY CLAIMS THAT THEIR COOKWARE IS EVEN-HEATING, BUT IS THAT TRUE?

The job of stovetop cookware is a) to smooth out the uneven heat coming from the burner underneath so that the entire cooking surface of the cookware is the same temperature; and b) to keep your food in the Maillard reaction temperature zone–not too hot and not too cold. If you have too much of an imbalance in temperatures, you wind up with hot or cold spots that can undermine your dish by leaving some food overcooked and some food undercooked. You may even scorch carcinogens into your food or produce carcinogenic smoke, if some hotspots grow hotter than the oil’s smoke point while you are waiting for non-hotspots to catch up in temperature. (Hotspotting is particularly troublesome on nonstick pans because you can overheat the hotspots when trying to bring up the temperature of the colder spots, and overheating PTFE/Teflon will permanently damage it and cause offgas.) If you’ve ever cooked fish where part of a fillet got overcooked while the rest was undercooked or made rice and had some undercooked while the rest burned, then you’ve already experienced the joy of uneven heating.

The larger the diameter of your cookware bottom relative to the diameter of the flame or heating element or induction coil, the bigger the uneven heating problem can be, since heat has to travel a longer distance to reach the sides.1

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Show 1 footnote

  1. Gas is somewhat less demanding on cookware than induction. With induction, heat goes into the circle above the induction element and then spread out from there. With gas, the flame heats a hotspot “O” shaped circle, but hot combustion gases help spread the heat some more by pooling up under the pan and then eventually spreading out and up and over the bottom of the pan, heating the sidewalls as well. If the sidewalls are made out of thermally conductive material (i.e., has some aluminum, copper, or cast iron/carbon steel), the sidewalls will absorb some heat and reduce the temperature difference between the edges of the pan and the center of the bottom of the pan. Note that these hot gases are much cooler than the flame, so you still get hotspots on gas, just less so than on electric/induction.

    Also, if the bottom of a pan is larger than the hotspot diameter (which for electric is the diameter of the coil), then you will NEVER get edge-to-edge even heating no matter how long or how low you preheat a pan on the stove, especially for poor thermal conductors like cast iron. That’s because the pan is bleeding heat energy into the air at the same time that the burner is injecting heat. (And contrary to popular belief, cast iron does not bleed heat more slowly than stainless.) There will always be a thermal gradient. You can try this yourself at home with a metal pan and thermocouples: preheat it on a very low setting for as long as you want and you will still see a temperature difference between the center and edge of the pan. Be careful not to overheat your pan, especially nonstick pans which can emit fumes. ↩

Even Heating Cookware: Why Even Cooking Matters And What We Can Do About It

WHY DO WE WANT EVEN HEATING AND WHAT CAN WE DO ABOUT IT?

The main job of the stovetop cookware is to smooth out the uneven heat coming from the burner underneath so that the cooking surface of the cookware is the same temperature. If you have too much of an imbalance in temperatures, you wind up with hot or cold spots that can undermine your dish and your health by leaving some food overcooked and some food undercooked. You may even scorch oil and produce carcinogenic smoke, if some hotspots grow hotter than the oil’s smoke point. If you’ve ever cooked fish where part of a fillet got overcooked while the rest was undercooked; if you’ve ever made rice and had some undercooked while the rest burned; if you’ve ever burned part of a strip of bacon while waiting for the ends of the strips to be done, then you’ve already experienced the joy of uneven heating.

A second job of cookware is to hold that heat so as to maximize Maillard reactions. These reactions take place at higher temperatures. Thus if you have a flimsy pan and tossing in a steak crashes the temperature, that will mean more steaming/boiling of your food and lower Maillard reactions, resulting in less-tasty food.

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Cookware Material: Tin

Cooking surface: 2/5 Poor (fragile, low melting point)
Conductive layer: N/A (tin is never the main heat conductive layer)
External surface: N/A Poor (tin is too soft for exterior use)
Example: Mauviel
Health safety: 4/5 Good (tin is mostly but not totally non-reactive)

—–

DESCRIPTION AND COMPOSITION

The bottom of this new pot was heated by an uneven heating element. The tin that was exposed to temperatures above 322F softened. Even when the tin cooled down, it no longer looked pristine. The sides of the pot never reached softening temperatures, nor did a crescent-shaped portion of the bottom of the pot. (This pot was taken off the burner soon after the tin started to soften.)
The bottom of this new pot was heated by an uneven heating element. The tin that was exposed to temperatures above 322F softened. Even when the tin cooled down, it no longer looked pristine. The sides of the pot never reached softening temperatures, nor did a crescent-shaped portion of the bottom of the pot. (This pot was taken off the burner soon after the tin started to soften.)

Tin is an extremely soft metal that you can scratch with your fingernail.1 Tin transitions from shiny “beta” tetragonal tin to rhombic tin between 161C and 202.8C (321.8F and 397.04F).2 It’s still tin, just in a different crystal arrangement and slightly less shiny. Tin melts at 231.9C (449.42F).3

Tin is used in copper cookware as a lining because tin resists corrosion, is nontoxic, and is relatively non-reactive compared to bare copper. Ingesting large amounts of copper can lead to negative health consequences, so always have your tin-lined copper re-lined once you see large bare areas of copper peeking through.4

IS TIN TOXIC?

Tin is not toxic in small amounts, especially elemental tin, hence the proverbial “tin can” for food.5 Unless you plan to gnaw on your tin-lined cookware, it should not be a problem to absorb a milligram here or there from tin.

TIN-LINED COPPER VS STAINLESS-LINED COPPER

Frankly I would avoid both since copper cookware tends to sell for small fortunes, and you can get thick aluminum for much cheaper and at a lower weight and still get very good thermal conductivity.

But if you must have copper than stainless-lined is the way to go for most people. Here’s why:

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Show 5 footnotes

  1. http://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness ↩
  2. http://tin.atomistry.com/rhombic_tin.html See also Matweb.com listing for elemental tin under “beta” or “white” tin. ↩
  3. Note that copperware manufacturers like Baumalu claim to use lead-free tin, to avoid lead poisoning, and I have no reason to disbelieve that. Nevertheless, there could be some nontoxic impurities in their tin so that their tin doesn’t quite follow these temperatures exactly. ↩
  4. http://en.wikipedia.org/wiki/Copper_toxicity ↩
  5. See, e.g., TOXICOLOGICAL PROFILE FOR TIN AND TIN COMPOUNDS, U.S. Department of Health and Human Services Public Health Service (TSDR), August 2005, accessed at http://www.atsdr.cdc.gov/toxprofiles/tp55.pdf ↩

Cookware Even Heating Rankings (Induction and Electric Coil, Radiant, and Halogen)

A <a href="https://www.centurylife.org/in-depth-product-review-demeyere-atlantis-and-john-pawson-11-inch-4-2-quart-28-cm-4-liter-saute-pan/">Demeyere saute pan with 2 mm thick copper bottom (28cm)</a>
A Demeyere saute pan with 2 mm thick copper bottom (28cm)

For natural gas/butane/propane rankings, please see Even Heating Rankings (Gas). For details about testing methodology, see here. The pans tested below were tested on an induction cooker. If you’re in the market for a portable/countertop induction cooker, I wrote an extensive guide here.

SEEMINGLY EVERY COMPANY CLAIMS THAT THEIR COOKWARE IS EVEN-HEATING, BUT IS THAT TRUE?

The job of stovetop cookware is a) to smooth out the uneven heat coming from the burner underneath so that the entire cooking surface of the cookware is the same temperature; and b) to keep your food in the Maillard reaction temperature zone–not too hot and not too cold. If you have too much of an imbalance in temperatures, you wind up with hot or cold spots that can undermine your dish by leaving some food overcooked and some food undercooked. You may even scorch carcinogens into your food or produce carcinogenic smoke, if some hotspots grow hotter than the oil’s smoke point while you are waiting for non-hotspots to catch up in temperature. (Hotspotting is particularly troublesome on nonstick pans because you can overheat the hotspots when trying to bring up the temperature of the colder spots, and overheating PTFE/Teflon will permanently damage it and cause offgas.) If you’ve ever cooked fish where part of a fillet got overcooked while the rest was undercooked or made rice and had some undercooked while the rest burned, then you’ve already experienced the joy of uneven heating.

[Read more…]

Electric vs Natural Gas (or Butane Propane etc.) vs Induction Cooktops and Ranges

SUMMARY

I’ll cut to the chase for those of you who want the bottom line. If you want the most even heat in a residential cooktop possible regardless of drawbacks, get either multiple-ring gas or an induction cooktop that has dozens of little induction coils. Those tend to cost quite a lot, though. For everyone else, if you can afford it, get induction, as it strikes a great balance, though the upfront cost is still relatively expensive. If you can’t afford induction, get gas (assuming you already have the gas line and ventilation ready to go). If you can’t get either, get electric radiant, and if you can’t get that, get electric coil (same thing as electric radiant, but harder to clean). Also consider hybrid induction-gas ranges if you have a piece of induction-incompatible cookware you absolutely can’t let go of, or use woks a lot to stir-fry, as most induction cooktops struggle with both. Frankly, though, I’d rather just get a portable gas stove for those situations. [Read more…]