“If metals are such a good conductor of heat,” a reader recently asked, “then how does my cast iron skillet’s handle stay cool, even when the skillet is hot?”
One of the top misconceptions we tend to have about cast iron is that, because it makes for such good cookware, it must therefore be an excellent conductor of heat.
To the great surprise of many, exactly the opposite is true.
Cast iron makes for great skillets, grill pans, and Dutch ovens because it’s a poor conductor of heat. That’s why cooking vessels made of cast iron take longer to heat up but, once they’re there, they keep a steady cooking temperature and distribute heat evenly, without cold spots.
How does cast iron weigh up to other metals, then?
The thermal conductivity of cast iron is 52 Watts per meter-Kelvin (W/m K), compared to 54 W/m K for carbon steel, 237 W/m K for aluminum, and 413 W/m K for copper (via Engineering Toolbox).
In other words, cast iron is 4 1/2 worse at conducting heat than aluminum, the most prevalent choice of metal for ceramic and non-stick cookware, and 8 times worse than copper, the metal of choice for some of the highest-end cookware manufacturers in the world.
That being said, stainless steel is a worse heat conductor than cast iron. The thermal conductivity of Grade 304 stainless steel, the grade of steel that most pans and pots are made of, is 14.4 W/m K.
|Stainless steel||14.4 W/m K|
|Cast iron||52 W/m K|
|Carbon steel||54 W/m K|
|Aluminum||237 W/m K|
|Copper||413 W/m K|
These figures tell us a few things:
First, it clearly takes longer to preheat a cast iron skillet than it does a non-stick or copper pan.
If you own more than one piece of cookware at home, you’ve probably seen this yourself. No matter what kind of stove you cook on, a non-stick pan will heat up almost instantly, while cast iron can take a good 3-4 minutes before it gets hot.
Second, cast iron pans and pots are less responsive to adjustments of the heat dial and take a relatively long time to release the heat that they’ve accumulated during cooking. This explains why a Dutch oven can keep your food warm for hours on end.
What Are Cast Iron Skillets Good For?
If you place a thick-cut steak in a hot aluminum or copper pan, the temperature of its cooking surface will drop almost instantly (and recover as fast). Do the same on a cast iron skillet or grill pan and measure the temperature with an infrared thermometer, and it will drop much less.
The same, by the way, applies to when you turn the heat on your range up or down.
Cast iron is great for searing a ribeye steak or cooking burgers, a task that requires constant and even heat. Less so for sautéing fish or mushrooms, where you need to adjust the heat of cooking quickly.
Cast iron cookware is also a good choice for baking. Just search for “cast iron baking recipes” on Google, and you will get back some 170 million results for things like cornbread, bread rolls, pizza, pie, cookies, and cake, among others.
A cast iron skillet is so good at holding on to heat, in fact, that you can generally substitute one for a pizza stone.
The trick to making cast-iron pizza work, for readers who are eager to try this out, is to preheat the skillet for 45 minutes to an hour in your oven, then place the pizza pie, untopped, on the hot surface shortly after shaping it.
The tall sides of the skillet won’t allow you the slide the pie onto the surface with the help of a pizza peel, as you’d otherwise do if you were using a baking stone or pizza steel. You simply need to open the oven and slightly pull out the rack until it’s easy enough for you to place the pizza on the skillet.
Once you’re there, add the toppings quickly, then close the range and bake your pizza until it comes out nice and airy.
The heat of your cast iron cooking vessel will puff up the dough and brown it—resembling the type of pizza you’d get served at Pizza Hut.
Foods That You Shouldn’t Cook In Cast Iron
Cast iron pans and pots are great for browning meats, like beef, pork, veal, lamb, and poultry, and cooking grains or starchy vegetables, like rice, beans, and potatoes. As we’ve already established, they’re also suitable for baking all kinds of goods in the oven.
Yet cast iron is not a good choice for overly acidic foods, like tomatoes, vinegar, lemon, and wine (or sauces that contain them). Cast iron has the tendency to react to the acids in your meals, leaching a hefty amount of dietary iron and imparting them with a metallic taste.
With its porous surface, cast iron catches the smell of whatever it is that you cook with it and can be pretty reluctant to let go of it for multiple uses after. That’s not necessarily a problem when you’re browning steak in butter, but it can become an issue if you cook salmon or whitefish.
So, for acidic foods and smelly fish, opt-in for cookware with a smooth surface—like stainless steel, ceramic, or non-stick—instead.
The Bottom Line
Ironically (pun intended), cast iron makes for good cookware because it’s a poor thermal conductor. Sure, it takes a few minutes for it to heat up. But, once it’s there, it distributes heat evenly and holds on to it well. You can use it for cooking all kinds of foods using a variety of cooking methods, as long as the ingredients are not overly acidic.
P.S. The secret to the handle not heating up too much? There’s a small hole at the end that allows it to radiate heat instead of accumulating it.
A lot of the beneficial properties of cast iron that you’re assigning to its low thermal conductivity are in fact due to it’s high heat capacity which is due to the fact that cast iron pans are thick.
Thanks, A, this is actually a very good point. I’ll deep-dive into this and give this article a factual update in the coming days!
This was a great, effective, article. Thank you, sir.