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Watch How an Enameled Cast Iron Cocotte is Made (Hint: With Fire!)

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A ladle, they call it. This vessel, the size of a large industrial oven, has just been poured full of molten cast iron that's over 2000º F. Now, it's being wheeled right past us, sputtering sparks and radiating heat, by a man driving a forklift at a somewhat high speed. Our whole team, led by our trusty founders Amanda Hesser and Merrill Stubbs, is either gaping or holding a phone up to capture the moment for posterity (and, okay, social media).

The draining dregs of a batch of molten cast iron made sparks fly like magic.
The draining dregs of a batch of molten cast iron made sparks fly like magic.

This day, our third in a trip to Europe earlier this fall, is just an average one at Staub's foundry in Merville, France, a pastoral little patch of Normandy dotted with farmhouses and narrow roads with sharp turns. We'd just driven there from Antwerp, on a mission to see how Staub makes their iconic enameled cast iron cocottes—a favorite in our test kitchens, Shop shelves, and homes.

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My most exciting learning during the visit, besides the difference between a foundry and a factory? (The former is a factory that produces cast metal, such as Staub's, and it sounds much lovelier.) Besides learning their that their Majolique finishes require an additional coat of enameling—three, compared to the two coats that one of their flat finishes requires—and far more testing on the color development end, to achieve their deep, liquid-like appearance?

This: The entire surface of a Staub cocotte is enameled—including the matte black surface you cook on, in addition to the colorful glossy exterior.

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And that interior surface is intentionally designed to be rough, unlike the outside. That's how it browns your food so effectively. (More on how they make it rough, here).

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Because that rough surface is actually a layer of glass (the meaning of "enameled"), and not just raw cast iron, it's also protected: You can cook all the acidic foods you'd like in an enameled cast iron pot, and wash it down with lots of soapy suds and water without worrying that it will rust. (Should you encounter any burnt-on grease on the pot's exterior, a little mildly gritty Bar Keeper's Friend will help you remove it without causing any scratches or harm.)

Simply put, it can do everything cast iron can—but without all the coddling and fretting.

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Of course, nothing so excellent comes easy.

A Staub cocotte requires a week to make, from raw ingredients to the packaging stage, and is touched by approximately 20 employees over the course of its production. Even so, their foundry is able to turn out several thousand a day. Our team, clad in hard hats and steel-toed shoe protectors, had the distinct pleasure of seeing every step of production during our visit, and we thought you might be interested in learning how the magic happens.

Here's how an enameled cast iron cocotte is made:

a recipe

In the same way that the basic recipe for bread is not unique—you'll need flour, water, and yeast, no matter what—the basic recipe for cast iron is standard: a mix of pig iron* (blocks of crude iron that have been extracted from iron ore), scrap metal (which contains a lot of important elements that make cast iron cast iron), and limestone (which does the job of extracting sulfur, and the undesirable properties it confers, from the scrap metal).

Clockwise from left: Limestone, scrap metal, and pig iron.

In addition to seeking out especially high-quality materials, Staub also tweaks the ratios, temperature, and furnace conditions to make their cast iron recipe uniquely suited for the task of becoming a cocotte. (In other words, they ensure that it's 100% food safe by weeding out things like lead in the raw materials.)

Using a massive magnet attached to a crane, each of these raw ingredients is transferred from heaps—"mountains," Merrill called them—outside the factory to the furnaces inside.

*Pig iron gets its name from the shape it takes when removed from the mold—the wiggly "tail" is the bit of hardened metal that ran through the channel, called gating, when it was cast into blocks.

the furnace

All this gets layered into one of a pair of cupolas, which are furnaces designed expressly for the purpose of melting cast iron. Cupolas range in size, but the two at Staub are an incredible 30 feet tall; at about 30 years old, they're like wise elders watching over the hustle and bustle of the foundry's affairs.

Coke, a kind of high-carbon fuel made from coal, is also added to the mix of ingredients, then set on fire to generate the heat. Within about 45 minutes, the mix is molten (at a mind-boggling 2550º F).

From furnace to ladle.
From furnace to ladle.

Enter, the forklift. That cauldron-like ladle is raised up to a spout at the base of the cupola; a stopper is removed so that the molten cast iron can flow freely through, from cupola to ladle. It's so bright that it ceases to be a color when you look right at it, like a beam of liquid light.

One the ladle is full, a worker shuts the valve and another putters the batch over to the next station on said fork lift. There, it'll be poured into molds.

And then into the sand molds with you.
And then into the sand molds with you.

Once the entire cupola-worth of molten cast iron is drained and transferred to the next station, the residue needs to be removed so the furnace can be cleaned. That same forklift picks up a long makeshift ramming beam and jams it repeatedly into the opening to free the refuse. It is not a gentle affair.

What sputters out is so hot that it looks like more of the same lava, but it's actually the molten limestone (and the impurities it captured) that rose to the top of the batch. "Slag," they call it—if you're keeping tabs on all these terms!

Slag, being skimmed out into a container for disposal.
Slag, being skimmed out into a container for disposal.

Once the slag cools a little, it's picked up by our friend driving the fork lift...

NBD.
NBD.

...and dumped out back, smoldering into prehistoric-looking pyramidal blocks. (We walked by these tame-looking boulders and had to stand back—they're still radiating an incredible amount of heat.)

Semi-cooled blocks of slag from the cupola.
Semi-cooled blocks of slag from the cupola.

At the end of every day, the cupola that was just in use must be thoroughly cleaned. After waiting a few hours for it to cool down, a worker is lowered inside the furnace—an opening that is, by the way, a mere 30 inches in diameter—with a jackhammer. With it, he dislodges the remnants of fireproof coating so that a fresh coating can be sprayed on (the protective coating only lasts through a single batch). This task will take between two and three hours, and it has to be done every single day.

The next morning, before the ingredients are added for a new batch, the same worker (who is very brave) goes back down into the 30-foot furnace to spray on a fresh fireproof lining, which will take between three and four hours. This is how his shift starts, every day, something I now remind myself when griping to myself about getting on the subway in the morning.

As you might imagine, this job requires not just gusto (and a lack of claustrophobia) but also technical precision: There are only a few workers who hold this position, and they're trained for six months before they can do it. At present, the cupola workers are all men.

The gentleman we had the distinct pleasure of observing do his job (he was the person driving the forklift around, but he's also no stranger to fireproofing the furnace) was excited to have a captive audience—especially so that he could show the video we put together to his wife.

When Zwilling J.A. Henckels bought Staub and took over this foundry in 2008, they introduced a world of new safety measures—especially for the cupola-cleaning and lining jobs. The person replacing the lining of the furnace wears a carbon monoxide detector and a position sensor, which will trigger an alarm if he stops moving.

Fireproofing the furnace.
Fireproofing the furnace.

They even offered our friend a new gig: Perhaps he might not want to clean a hot, 30-foot deep by 30-inch wide furnace every day if given the option? But to their surprise, he refused. The cupola cleaner before him, who held the position for sixty-plus years, was his dad. So it's family tradition.

And so you don't lose sleep over it, Staub takes every safety precaution possible. And they plan to eventually upgrade to modern, induction-powered furnaces—at no small cost, of course—in the future.

The cupola during prime time (yes, it was this glorious in person).
The cupola during prime time (yes, it was this glorious in person).

molds and casting

Now back to that molten cast iron. It's hauled over to a conveyor belt lined with molds that are made of pressurized sand, and poured right in like they're making chocolates. Cocotte-shaped chocolates. Molten chocolates. Anyway.

1700 pounds of melty, lava-like cast iron gets poured from a ladle into the sand molds.
1700 pounds of melty, lava-like cast iron gets poured from a ladle into the sand molds.

These sand molds are also made in the foundry, by pressing quantities of fine black sand between two pattern plates at very high pressure. (The pattern plates, once upon a time also cast by hand, are now made by machine—just one of their many advancements that ensure consistency and efficiency.)

Like every material we encountered at Staub, the sand used to make the molds is of a particular quality.

Baby cocottes in their formative years (okay, hours).

Staub gets the sand, which is prized for being extra-fine, from a town near Paris. French sand for French pots, obviously—but its properties actually do play an important role here, defining the surface structure, or roughness, of the exterior of the cast iron cocotte so that the enamel coating sticks.

Mixed with carbon to prevent it from reacting with the molten cast iron, the sand appears black when it's pressed into these molds. One half of a mold has a cocotte-shaped recess in it; the other half has a cocotte-shaped protrusion. When they're fit together, there are tiny pathways for the cast iron to flow through so that it reaches all the nooks and crannies of the cocotte shape. These are called "gating."

Squirt.
Squirt.

The size, shape, and route of the gating in the sand molds isn't just complex—it's top secret! (Hence our lack of photo evidence.)

Too wide a path, and the molten liquid will move so quickly that it breaks the sand mold; too narrow, and it will solidify in its tracks, clogging the gating system. But narrow it needs to be, because underneath the enamel coating, a cocotte's walls are just three to four elegant millimeters thin. Hence why every factory has a different gating system, always proprietary, because they're a feat of engineering in and of themselves.

Even though the sand molds are crumbly to the touch, the molten cast iron doesn't warp them.
Even though the sand molds are crumbly to the touch, the molten cast iron doesn't warp them.

Back to our cocottes: After cooling for a little while, all in a row, the sand molds are broken open and the cocottes fall out. They call this very loud, very bouncy, very hot process the Shake Out.

the shake Out

Shake, shake, shake.
Shake, shake, shake.

It's a little alarming to see somebody take to a newborn, still-warm cocotte with a hammer, but these workers are actually just dislodging the big chunks of remaining sand and pieces of the gating (and the jumpity conveyor belt helps loosen the rest of it).

And thus starts another life cycle: Even though a sand mold only makes a single cocotte before it's broken apart, the sand itself is recycled to make molds over and again and again. At any given time, there are some 250 to 300 tons of it in use at the foundry.

The cycle goes like this: Post Shake Up, the sand is gathered up and cooled down, then re-hydrated (some moisture is lost when the molten cast iron goes in), then dried again and restored to its original pristine condition—before being pressed into another set of molds to make another round of pots.

clean up

With most of the sand removed, the cocottes (and lids!) are now ready to be cleaned. This process, called shot blasting, involves shooting tiny pieces of steel at the cocottes to remove any lingering residue.

This process was once entirely done by hand—and still sometimes is, as in the case of certain super detailed shapes like our beloved pumpkin cocotte that requires a deft range of motion to get all its curvatures smooth. But these days, it's typically handled by robots with lifelike long arms that grip and twist around the cocottes so that they can be carefully cleaned.

Freshly shot-blasted and grinded cocottes.
Freshly shot-blasted and grinded cocottes.

From there, the cocottes go through a grinding process to remove the burr, or any remaining bumpiness on the exterior.

And after that, a final shot blasting step: This evenly removes the thin, outermost layer of the surface of the pot (which is largely oxides) so that, mechanically and chemically, the enamel coating can adhere to it.

Primed and ready for a paint job.
Primed and ready for a paint job.

At this stage, the cocottes are essentially mint condition unseasoned cast iron—but they're destined for even greater greatness.

enameling

At present, Staub offers 8 different colors of enamel (and matte black). You might be wondering why they don't offer more.

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Our exclusive blue-and-brass Staub line features a "flat" navy finish; while our grenadine pots, with their subtle gradation, are Majolique. Both have matte black interiors.

"We're not in the fashion business," is how an engineer put it while we were standing in the enameling lab at the factory. He went on to say that they vet their colors to be classic and enduring, rather than every hue of the rainbow. Some are solid colors, like our exclusive navy with brass handles collection, and others, like our grenadine, have a deeper, almost watery spectrum to their finish that Staub calls "Majolique."

Color studies.
Color studies.

While I'm impressed by the fact that it apparently takes months for their chemists to formulate a new color, they're always aiming to be even faster.

But it's complicated: Enamel isn't made by just selecting a paint from a can. Staub's chemists are formulating solutions that will turn out consistently in an environment where variables constantly fluctuate: If the kiln gets too dirty, for example, it can throw off the color of a whole batch.

This baby blue lid will turn royal blue when it's fired (remember, from pottery class?).
This baby blue lid will turn royal blue when it's fired (remember, from pottery class?).

The enamel surface, like the cast iron, comes from a recipe: frits (which are glass chips about the size of flakey salt) oxides (or "pigments"), clay, and a little bit of water go into a big barrel called a ball mill, along with baseball-sized ceramic balls that pummel the mix to a slurry.

"A little bit like mud," is how they describe the consistency. Every batch of enamel is tested to be sure it falls within a certain tolerance range—not too opaque, not too translucent, not too thick, but just right. While it's a easy-ish to get the recipe and therefore the color right, it's much more difficult to get the slurry to be a consistent grain and thickness (and you'd be able to spot that difference on a finished cocotte right away).

The matte black enamel, which is so important for browning foods, is actually a mix of two different kind of glass frits that have slightly different melting points. So when one melts completely in the kiln, the other only melts partially, so that the surface stays slightly coarse.

The insides get sprayed with two coats of matte black enamel.
The insides get sprayed with two coats of matte black enamel.

From here, the enamel is pumped through spray guns that mist it all over the cocottes as they spin on little moving stands. A flat color gets two coats: On the inside, primer followed by matte black, and on the outside, primer followed by a glossy color (or black).

A Majolique color, on the other hand, gets three: Primer followed by matte black on the inside, same as a flat color, and then primer followed by two coats of glossy color on the outside. The first of those exterior coats is always the lighter of the two, resulting in a dewy gradation at all the edges of the pot.

Twirl ballerina, twirl!
Twirl ballerina, twirl!

Spinning on the conveyor belt, they look a bit more like dancers in a colorful mist than cocottes getting coated with glass. But the spray nozzles know otherwise: They need to be replaced constantly, as the fine grain of the glass slurry grinds away at the nozzle over time. This is no simple coat of spray paint.

Freshly enameled and ready for the oven.
Freshly enameled and ready for the oven.

After two (or three) coats by the machines, plus detail work on the handles that's done cocotte by cocotte by hand, they're dried and then fired at 1470º F for twenty minutes. Piece of cake.

In you go, friends!
In you go, friends!

The most popular colors? They vary by region: Japan seems to like subtler hues, like sand, while China likes white, and red more than blue. In the states, red and blue are both popular. In France, the restaurants all get black.

Quality Assurance

After the cocottes are fired and cooled, they move onto quality testing. Three products from each color batch of roughly 1,000 to 2,000 are sacrificed to see how they stand up to rigorous testing (and every cocotte is visually inspected to be sure it looks like it should).

Post-trauma testing, to be sure the surface stays intact after impact. (Grade: A+)
Post-trauma testing, to be sure the surface stays intact after impact. (Grade: A+)

One of the most important (and toughest) of these quality tests is for thermal shock, because glass and iron have very different rates of expansion under heat. For the test, a cocotte is submerged in cold water after it's been warmed to be sure the batch can withstand normal changes in temperature in your kitchen.

Note, however, that this is an extreme-condition lab test, purely intended to check standards; Staub recommends never placing your hot cocotte in a sink full of cold water. (And we recommend never doing that to any of your cookware—it's the quickest way to damage a pot or pan!)

A batch of grenadine cocottes, fresh from the kiln.
A batch of grenadine cocottes, fresh from the kiln.

In addition, they test for acid resistance to be sure the enamel coating is even and protective, and impact resistance to be sure the surface doesn't shatter if it's dinged around in the kitchen (those are the dots you see on the pots above). They also test to be sure the cocottes are working on induction surfaces—and they do, thanks to the cast iron.

The underside of all cocottes are a glossy glaze, so they'll never scratch your stovetop. And in the case of the matte black cocottes, which are otherwise coarse allover, that smooth underside is a pleasant foresty green. It's a little like a flag being waved to the customer saying, "Don't worry, I'm smooth and enameled!" so they aren't afraid to use it on a stovetop.

Did you know your black cocotte has a green bum?
Did you know your black cocotte has a green bum?

This very foundry has been churning out Staub's cast iron cookware since 1974, which is why so much of the process still has an old-world feel. With, of course, modern safety measures: Employees are only allowed to work one 8-hour shift before they're cut loose for another team to come in and oversee the next half of production. All pedestrian traffic is separate from the machinery doors and pathways, and we had to suit up like this to be allowed to safely roam about.

Ready for a 120-degree furnace factory field trip! #f52abroad @staub_usa

A video posted by Amanda (@mandasims) on

Which, quite frankly, we loved. (Even though it was a no-big-deal 120º F inside the factory on the day we visited.)

Our trip to the Staub foundry was, as I'm sure is evident, unforgettable. There won't likely be another day in my life where I'm served a five course meal featuring a life-changing bread-and-cheese course, and then taken on a tour of a enameled cast iron foundry, miles from anything in the fields of northern France. They had an American flag flapping on the flagpole for our arrival. And let us take Boomerangs of their cupolas spouting molten cast iron. We got a little weepy saying goodbye.

And while we weren't surprised that such incredible lengths are taken to make this cookware, which we already very much admire, we were undoubtedly amazed. This weekend, I'll hopefully make a turkey without failing; everyday at Staub they make thousands of pristine, long-lasting cocottes. Thankful is how we feel.

Team Staub.
Team Staub.

Andrew Reed Weller—above, with camera—was our Director of Photography on the trip.

Factory photography by Craig Rockwell.

A special thanks to all our friends at Zwilling and Staub who made this trip, and this story, possible. Check out all our Staub in the Food52 Shop, and tell us what you love to make in yours in the comments.

Tags: Staub, cocottes, cast iron, enameled cast iron