Equipment: How to Buy, Season, and Maintain Cast Iron Cookware
Each week J. Kenji Lopez-Alt will drop by with a list of tools or a tool you might want to stock your kitchen with—if you haven't already. Kenji also writes The Food Lab column here on SE. You can fan The Food Lab on Facebook for play-by-plays on his future kitchen tests and recipe experiments.—The Mgmt.
Having just adopted a French bulldog named Dumpling, I'm quickly finding out that taking care of a puppy is very similar to taking care of a good cast iron pan, and in some ways, almost as satisfying. They both require a little work, a little patience, and a whole lot of loyalty. The main difference is that in return for my investment, my cast iron pan gives me golden-brown fried chicken, sizzling bacon, corn bread, apple pies, charred hash, perfectly seared steaks, bubbly pizzas, and, yes, crisp dumplings. Dumpling the puppy, on the other hand, gives me mostly licks, chews, and a whole lot of poop. You do the math.
As far as retaining heat goes, nothing beats a good, thick cast iron pan. Its density means that it takes a long time to heat up—I give mine a good 5 to 7 minutes on the fire—and doesn't cool down very much when you add food to it. So while a thin aluminum pan may drop by as much as 300°F when you add a half-pound rib eye steak to it, a cast iron pan will stick close to its original temperature, delivering a thicker, crisper, more evenly browned crust. Similarly, you can get away with using a little less oil when frying your chicken, since the heat retained by the metal will rapidly reheat the oil as soon as the chicken cools it down.
The fact that its oven-safe means that you can braise and bake in it just as well as you can fry or sear. Cornbread comes out with a beautiful golden-brown crust, and pies come out wonderfully crisp on the bottom, even with moist fillings. It's heat retention abilities means that even when your oven's temperature fluctuates up and down (as most thermostat-driven ovens do), your pan's heat will stay fairly constant.
And talk about durability! Cast iron cookware is one of the few items in your kitchen that actually gets better the older it is. The very best pans have been passed down sometimes over multiple generations, their well-used surfaces worn as smooth and nonstick as a Teflon-coated pan, without the toxic chemicals. Cast from a mold in a single piece of metal, there are no welded joints or even rivets to wear out.
There are, of course, a few downsides:
- Until a good layer of seasoning has built up, food will stick to it. This goes for even the "pre-seasoned" skillet on the market now, which have a mediocre level of seasoning at best. With everyday use, a cast iron skillet will be perfectly seasoned (I define this as nonstick enough to cook eggs in) within a few weeks. With less frequent use, you can expect the process to take a couple of months. It's a long haul, but just like housebreaking a puppy, think of how proud you'll be when that first egg slides magically off the bottom
- It heats unevenly. Contrary to popular belief, iron is a poor conductor of heat, which means that the heat doesn't travel far from its source. Trying to use a 12-inch cast iron skillet on a 3-inch burner ring is an exercise in futility: the outer edges of the pan will never get hot. To effectively heat a cast iron pan, you need a large burner, and plenty of time for even distribution (see Cooking Issues for a good visual of this in action)
- It can rust. While a good layer of seasoning will prevent this from happening, carelessness (like scrubbing or not allowing it to dry thoroughly after use) can lead to rust spots
- You can't cook overly acidic foods in it. Acidic foods will pick up flavor and color from the iron, turning them dingy and metallic-tasting. This means that until a very good layer of seasoning has developed, quick wine-based pan sauces are out of the question, as are acidic dishes like tomato sauce
- It's heavy. There's no getting around this one. The density of the material is what makes it so good at retaining a large amount of heat energy in a small amount of volume. Innovations like helper-handles help, but smaller cooks will probably struggle on tasks like flipping or pouring
- It requires special cleaning. Because the quality of cast iron cookware is dependent on how well seasoned it is, care must be taken while cleaning to prevent accidentally removing the layer of seasoning or you're gonna have to start from scratch
All that said, there's really not much to it when it comes to seasoning, maintaining, and storing your cast iron cookware. Here's a quick guide:
When you first get your cast iron pan, it will have either a bullet-gray dull finish (for an unseasoned pan), or a black, slick-looking surface (for a preseasoned pan). Unless you are buying a 75-year-old pan from a garage sale, your pan will also have a pebbly-looking surface like this one:
Modern cast iron is bumpy like this because it has not been polished the way old cast iron has and retains some texture from its mold. Some people claim and that it's not possible to season these bumpy pans properly. I don't buy it. I have compared my shiny, totally smooth 1930s Griswold (acquired at a flea market) to my 10-year-old Lodge skillet (which I bought new and seasoned myself) and have found no significant advantages with the old pan, other than the fact that I didn't have to season it to begin with.
So the key is all in seasoning it properly. How does it work?
Well, if you look at a cast iron pan under a microscope, you'll see all kinds of tiny little pores, cracks, and irregularities in the surface.* When food cooks, it can seep into these cracks, causing it to stick. Not only that, but proteins can actually form chemical bonds with the metal as it comes into contact with it. Ever have a piece of fish tear in half as you cook it because it seems like it's actually bonded with the pan? That's because it has.
To prevent both of these things from happening, you need to fill in the little pores, as well as creating a protective layer above the bottom of the pan to prevent protein from coming into contact with it. Enter fat.
When fat is heated in the presence of metal and oxygen, it polymerizes. Or, to put it more simply, it forms a solid, plasticlike substance that coats the pan. The more times oil is reheated in a pan, the thicker this coating gets, and the better the nonstick properties of the pan.
Here's how to build up the initial layer of seasoning in your pan:
- Scrub your pan by pouring a half cup of kosher salt into it and rubbing it with a paper towel. This will scour out any dust and impurities that may have collected in it prior to use. Wash it thoroughly with hot, soapy water and dry it carefully.
- Oil your pan by rubbing down every surface with a paper towel soaked in a highly unsaturated fat like corn, vegetable, or canola oil. Unsaturated fats are more reactive than saturated fats (like shortening, lard, or other animal-based fats), and thus polymerize better. It's an old myth that bacon fat or lard makes the best seasoning agent, probably borne of the fact that those fats were very cheap back in cast iron's heyday
- Heat your pan by placing it in a 450°F oven for 30 minutes (it will smoke), until its surface is distinctly blacker than when you started. An oven will heat the pan more evenly than the stovetop will, leading to a better initial layer of seasoning
- Repeat the oiling and heating steps three to four times until your pan is nearly pitch black. Pull it out of the oven, place it on the stovetop to cool. Your pan is now seasoned and ready to go
Until you've got a good layer of seasoning built up, avoid excessive use of soap or cooking acidic sauces, as both can make the process take longer.
People are irrationally afraid of caring for cast iron. The truth is, once you've got a good layer of seasoning, cast iron is pretty tough. You can't scratch it out with metal utensils. You can't destroy it by using soaps (modern dish soaps are very gentle on everything except for grease). To maintain and build on it, all it takes is to remember a few key points:
- Use it often. A good layer of polymers should build up slowly in thin, thin layers. This means using your pan as much as possible—particularly for oil-based tasks such as frying or searing. Avoid cooking liquid-based dishes in the pan until it has acquired a reasonably good nonstick surface
- Clean it immediately after use. Removing food debris is much easier from a hot pan than from one that has been allowed to cool. If you clean your cast iron skillet while it is still hot, chances are all you'll need is a tiny bit of soap, and a soft sponge. I'm particularly wary of this at dinner parties when a well-intentioned guest may decide to chip in after dinner and get a little too generous with the elbow grease, potentially scrubbing out some of my seasoning
- In most cases, avoid tough abrasives. These include metal scrubby scouring pads, and cleaners like Comet or Bar Keepers Friend. The scrubby side of a soft sponge should be plenty for most tasks
- Dry thoroughly, reheat it, and oil it before storing. After rinsing out my pan, I replace it on a burner and heat it until it just starts to smoke before rubbing the entire inside surface with a paper towel lightly dipped in oil. Take it off the heat, and let it cool to room temperature. The oil will form a protective barrier preventing it from coming into contact with moisture or air until its next use
Worst Case Scenarios
There are basically only two really bad things that can happen to your cast iron cookware—scaling and rust—and neither of them is that bad.
The photo on the left shows a cast iron pan that has undergone scaling. This happens when you heat the pan too often without adding extra oil to it. Rather than coming off in microscopic bits like normal seasoning will, the layer of polymers sloughs off in large flakes. To reach this state, I stored my pan in the oven for a month's worth of heating cycles without reoiling the surface in between heating. It's easy to avoid this problem by regularly oiling the pan after each use and not overheating it (don't leave it in the oven during the cleaning cycle, for instance), but once it happens, there's no turning back—you'll have to reseason it from the start.
The photo on the right is a spot of rust that appeared on a cast iron pan that was not seasoned well enough and was left to air-dry. Water came in contact with the iron, causing it to rust. Unless the entire pan has rusted (in which case, you'll have to reseason the whole thing), this one is not much to worry about. Rinse it out with water, dry it, heat it up, and rub it down with oil. After a few uses, the rusted spot should be perfectly well seasoned again.
Which Pan Should I Buy?
If you're lucky enough to come across a reasonably priced cast iron pan from the early 20th century at a yard sale or flea market (say, under $50 or so), scoop it up immediately. You can occasionally also find good deals on eBay and sites like it.
I personally find it ridiculous to pay the $150-plus that some sellers are asking for old cast iron when a new cast iron pan, like the 10 1/4-inch Seasoned Cast Iron Skillet from Lodge costs a mere $16.00 and will give you an equally lustrous nonstick surface with just a bit of time and care.
* These are not to be confused with the bumps and dimples you can see on the surface with your naked eye, which have no effect on its nonstick properties.
About the author: J. Kenji Lopez-Alt is the Chief Creative Officer of Serious Eats where he likes to explore the science of home cooking in his weekly column The Food Lab. You can follow him at @thefoodlab on Twitter, or at The Food Lab on Facebook.