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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. 

The Incredible Egg

The Incredible Egg

Maybe you knew it as “eggs in toast.” “Eggs in a hole,” or “eggs in a frame.” Or perhaps the more common but still curious “toad in a hole,” or “frog in a pond.” But whatever your family called it, at some point in your life, you ate this egg dish of many names.

And wherever you grew up, be it on the Chesapeake Bay or Bayou, it was always the same simple recipe: butter in a pan, a slice of white bread, its center cut out, and an egg, any egg, cracked and fried inside.

But after all the generations it’s been passed down, after all the kitchens in which it’s been cooked, and all the tables and countertops and laps on which it’s been eaten, the question remains: which came first?

Though, with most of these colloquialisms spread by word-of-mouth, and with very little about them saved to history, it looks like we might never know 

A few things we do, predominantly from pop culture: the lesser-known “gashouse eggs” was likely derived from the German word gasthaus, for an inn or country home, and it was mentioned the 1941 Betty Gable film, Moon Over Miami. A few years earlier, the even-lesser-known “Guy Kibbee Egg” was dubbed for the early actor of the same name, who ate said eggs in the 1935 Mary Jane’s Pa, before going on to star in Mr. Smith Goes To Washington.

Of course, if we had our druthers, the Oscar would go to a cameo in the 1987 cult classic, Moonstruck, starring Cher and Olympia Dukakis, who fries up a delectable-looking version with roasted red peppers and olive oil. Known as uova fritte nel pane in Italy, it graced many an Italian-American plate in the first half of the 20th century.

Still, we may never know the nativity of, let alone namesake behind, “one-eyed Jack,” or “one-eyed Pete,” or exactly why it would ever be called a “cowboy egg.” And whether “Rocky Mountain Toast” was dubbed in Colorado, Montana, or Wyoming.

To make matters even more confusing, “egg-in-a-basket” and “egg-in-a-nest” are also common names for those baked egg-hash brown breakfast cups that consume the pages of Pinterest. And the aforementioned amphibian appellations are actually more truly a British dish of sausages cooked in Yorkshire pudding.

“Egg-with-a-hat,” which appeared in Fannie Farmer’s lauded Boston Cooking School Cookbook, starting in the 1890s? Now you’re just being ridiculous.

Maybe, in lieu of any legendary origin stories, the better question is: what’s in a name, anyways?

Perhaps—whether it’s served with white or wheat or sourdough, with its middle cut out by a cookie cutter or biscuit cutter or whatever you have on hand, with yolks as bright as a canary or dark as an oriole, topped with just salt and pepper or hot sauce or Worcestershire or pimento cheese, as done by those readers in the comment section of The New York Times’ recipe—this pan-toasted-bread-with-a-fried-egg-inside should simply be known as the great unifier.

Even with dozens of names, these mystery eggs continue to comfort us across centuries and cultures, and whether they’re eaten in a city walkup or over a country sink or outside in the mountain air, they always taste like wherever we came from—and like that first time we had them, all those years ago.

They might simply need no language, as all that’s really required is a hot cast iron, some bread, and fresh eggs. A spatula doesn’t hurt either.

After all, for most cooks, silence—albeit a few oohs and ahhs—is the greatest form of flattery, anyways.

Numbers Game

Numbers Game

What’s in a number? It’s a question commonly asked when it comes to cast iron, as these symbols—6s, 8s, 10s, and so on—were often inscribed onto the handle or bottom of many an antique pan.

For decades, numbers were staples of these skillets, so much so that new pan companies have started to numerically mark their own, paying tribute to the old practice. Which is one, it turns out, to be as useless today as our most recent Alma. (No offence to either.)

#1 Favorite

#0 Griswold

But like any good question, the answer is shrouded in its fair share of myth and controversy, though we do know that its origins date back just over two centuries, when the Age of Enlightenment would bring about many a pivotal innovation and invention, especially pertaining to our kitchens.

For our purposes, perhaps the most important development arrived on the eve of the 1800s with the process of standardization. Sure, we used measurements back in those days, but we still hadn’t figured out how much easier life would be if we just developed some standards, aka models to which we could compare things. In other words, through the 1700s, even as we created the influential likes of the lightning rod, the piano, the smallpox vaccination, we still had yet to make two nails—let alone skillets—that were exactly the same.

Standardization arose out of the Industrial Revolution, with standards implemented to both improve and increase production. Many say it all started with Eli Whitney, the New England inventor of the cotton gin, who in 1797 proposed the manufacture of flint-powered firearms with interchangeable parts. Up until that moment, each gun was made one by one, piece by piece, bit by bit, by the hands of a single gunsmith. But credit is due across the pond, too, to two Englishmen, Marc Brunel and Henry Maudslay, who were also then crafting identical pulleys and precision tools for shipbuilding, as well as an early production line.

#0 Griswold

#1 Favorite

With the invention of identical, interchangeable parts and products, manufacturers were able to make large runs of the same item for the very first time, while consumers could also now easily replace their worn-out goods. Standardization enhanced product uniformity and effectively quality, and as manufacturing advanced, so, in many cases, did the standard of living.

Exhibit A is the early cookstove, invented in the first half of the 1800s. A dramatic upgrade from open hearths in terms of cleanliness and safety, not to mention the overall experience of cooking, these enclosed stoves, eventually made out of cast iron, quickly became a fixture for middle-class homes.

Unsurprisingly, foundries got in on that craze, and with it, the making of cast-iron cookware as an easy add-on. These stoves had a variety of openings on their cooking surfaces, known as eyes, which ranged in size and effectively number, atop which sat different pots and pans. Thus, a cast-iron company’s number 3 stove eye paired with their number 3 skillet—an early standard! Sounds simple, right, but of course, it isn’t.

Contrary to popular belief, more often than not, these numbers did not equate to exact or even actual measurements, such as the diameter of the eye or pan, as proven by the Favorite 1, or better yet, the Griswold 0. On top of that, a Lodge 10 was not the same as the 10 of a Wagner, or any of the other guys, making for standardization within brand but missing the industry-wide memo.

Even as some companies shifted away from stoves, the numbers still stuck as the original pan patterns continued to be used for decades. Others closed, their records lost to history, only further intensifying the great debate over these numeric systems that has carried well into the 21st century.

Butter Pat Aunt Alma

Today, to make matters even more confusing, we’ve decided to use letters.

Where the handle’s base meets the pan’s rounded edge, you’ll find a small loopy squiggle—in fact, an initial—with each pan named in honor of a woman who has influenced us in some seminal way. They are mothers, wives, grandmothers, great aunts; maybe one day, sons and fathers.

We figured, since the numbers are antiquated with our modern stoves anyways, we might as well use a design element that means something, if only to us, and that tells a story, if only one just slightly less complicated. 

It is in indeed an homage to the past, to the tradition of numbering cast irons, to all of the practice’s legend and lore. But at the core, these letters, literally hand-drawn by our founder and located at the grip of our own fingertips, are meant to remind us about people.

About the former foundrymen who also inscribed early cast irons, using a simple stylus to carve those numbers right into the pattern’s clay. About Estee and Heather, Joan and Lili. Even little old useless Alma.

That they were here, and we were, too, before the measurements or mass production or machines took over. That hopefully we will be long after.

Little did we realize in the beginning, but with these names, the pans themselves would become personified—an unintended consequence but welcome embodiment, through the meals they make and the community they create in the kitchen, of what makes us human. Which, of course, is anything but standard.

Though, for that, in a way, we could call them standard bearers, too.