The Science of Cast Iron | Butter Pat Industries

The Science of Cast Iron

We chat with Southern chef Sean Brock about the thermodynamic properties behind the pan.

Okay, so we’ll tell you up front, this issue of the Standard Edition is going to be the Sean Brock Special. In part, because we love the guy, for his food, for his restaurants, and perhaps most importantly of all, for his big brain.

All photos courtesy of Peter Frank Edwards

Brock has been called many things—visionary chef, farm-to-table hero, Southern culinary revivalist, agricultural anthropologist—and we’ll add one more, which anyone who has eaten at his renowned McCrady’s in Charleston already knows: mad scientist.

For more than a decade, the James Beard Award-winning Chef’s Table star has been combining downhome fare with a forward-thinking philosophy, looking to the past to inform the future. “We are so young as a country,” says Brock. “There are so many traditions ahead of us that we haven’t even dreamt up yet.”

In the same way he’s dug into the roots of beloved Southern recipes, he has delved into the science of his kitchens with unbridled curiosity. And in few places has this been applied more than his cookware, and particularly cast iron, harkening back to his influential grandmother, whose home was littered with pots, pans, and farm equipment made out of the medium.

“When I was about 12, she bought me my first cast-iron wok and taught me how to take care of it,” says Brock. “It’s tricky if you’ve never cooked with it before. Now that I understand it from a scientific standpoint, I cook just about everything in cast iron.”

He likens it to a fast car, but vows that the more you use it, the more versatile it becomes. “Of course, the quality of the pan has to do with it,” says Brock.

Butter Pat: Tell us more about this fast car analogy, which we love.

Sean Brock: Just like a fast car, it can get away from you. It’s not as responsive as other pans—it’s slow to heat up, and if it gets too hot, it’s hard to cool down, which I think scares a lot of people. And it can be super dangerous when it gets out of hand. [Laughs.] But you need to be aware of that fact, and if you can respect it, you’ll ultimately have more control and better performance. You have to be patient. And the more you use it, the more you realize how versatile it is.

What are some of the qualities that make cast iron so versatile?

How it holds heat, once you get it to where you want it to be, for starters. It can stay at that temperature and evenly for a long, long time, which is good for cooking. That slow responsiveness can be used to its greatest advantage.

That said, a lot of people think cast iron is a good conductor of heat, but it’s actually the opposite, meaning that the pan does not easily give away its heat, especially compared to other mediums such as copper and aluminum.

Yes, and that’s definitely a myth that needs to be busted. I think a lot of people have that misunderstanding, myself included in the early days, based off the fact that cast iron can get really hot. That doesn’t mean it’s a good conductor of heat, that just means it can get really hot. And anything can get really hot with a fire underneath it. But a pan also isn’t judged based on its heat conductivity. It’s judged on how well it performs, and that performance is based off multiple properties.

For cast iron, that’s low conductivity, slow responsiveness, plus high reactivity, as well as density and thickness—how all of these things interact and impact each other. 

If you put all those factors down on a piece of paper and made a chart, you’d find that cast iron is actually the most balanced medium, much more so than any other cooking surface, and therefore, it’s the easiest to use, and the most useful, once you understand it.

What are some chef workarounds for some of cast iron’s thermal properties? 

In terms of being slow to heat up and slow to cool down, it’s patience and time. It’s like building a fire. And the key is getting to know your pan in the oven and on top of the stove. They’re different kinds of heat—you can obviously turn a flame on your stove up and down much faster than you can an oven—and the pan is going to react differently. Practice both and take notes. But you can also use the two in tandem. I keep my oven loaded with cast iron, all the time so they’re hot and ready to go. At the restaurant, we keep stacks near the fire so they’re the exact temperature we need them to be. Because of how they retain heat, they’ll sit there forever, perfectly happy and ready to use.

So you utilize your heat sources to mediate some of those thermal properties, which you discuss further in our Good Reasons piece on cornbread.

With cast iron, you have to think ahead about every step of the cooking process. Where the pan is going and what the movement of the pan is going to be. Moving from the oven to the stovetop is a variable that can throw off an entire recipe if you’re not paying attention. In some recipes, like cornbread, the pan goes in the oven first, then it goes on the stove with a burner on beneath it, because you’re about to be adding ice-cold batter and you don’t want the temperature to drop. This way, you’re creating an insurance plan in terms of maintaining temperature. And you can’t do that with any other pan, because they’re so quick to heat up and cool down. It just gets all over the place. 

On the other hand, iron is highly reactive, meaning it is more likely to chemically interact with other substances, like food or water, which is why cast iron is prone to rusting if left wet and can sometimes affect the color or flavor of a dish. Is this where seasoning comes in?

Seasoning basically acts as a barrier, a skin, an added layer of protection that slows down any potential reactions. If you season cast iron properly, you heat the oil so that it oxidizes and then polymerizes, filling the pores of the iron and make it less penetrable. Water inhibits a lot of things and slows everything down, so your goal is to get rid of it as fast as possible, especially when you’re trying to get crust or sear on breads or proteins or even vegetables. If there’s too much moisture, if you have too much steam, you don’t get the same textures, and you’re also diluting flavor instead of concentrating it. The beauty of a polymerized seasoning on a pan is that the built-up oil actually repels water and helps evaporate it as fast as possible.

How does the pan’s density come into play?

The density, and the thickness of the pan, is just as important as seasoning. It’s actually way, way more important than most people realize. This comes into play in how the pan actually transfers heat into the food. The density of the iron keeps the heat at a constant, with a density of thermal energy being transferred into the food. It’s like a slow, even flow that the low density of aluminum wouldn’t allow to happen. The thickness also makes it more reliable, because you know there aren’t going to be some spots that are hot while others are warm or cold. For me, that’s one of the most important advantages of Butter Pat pans. The thick bottom creates the most even caramelization of a crust that is humanly possible.

We’ve cast our pans to have thinner sides but a thicker bottom heat plate to better conduct and distribute heat. How does this compare to other cast-iron pans, like the beloved vintage ones we are passed down or pick up at antique stores?

The pans that we romanticize from the 19th and early 20th centuries were thin all the way around, which can cause hot spots, which is not good for cooking. But the Butter Pats are thick where they need to be, a detail that was closely paid attention to that often gets overlooked. How do you improve upon something that was already pretty amazing? Well, it’s those tiny little obsessive details that aren’t obvious to the eye that improve the whole thing slightly, in the same way that I try to approach food. We have these beautiful, wonderful, romantic traditions. But everything can always be better.

Even the physics.

You say “modern technology” and it freaks people out. But it’s this modern knowledge, and modern wisdom, that allows us to make small improvements on the past. Just like in cooking, and cooking Southern food, it’s enhancing tradition by moving it forward, and moving it forward by enhancing it.

Our thanks to Sean Brock for his time over the past two months as we put together this interview.