The truth about cast iron: Yes, you can use a little soap

Cast-iron pans are solid pieces of cookware that can last a lifetime, and they probably aren't as difficult to maintain as you have been told. J. Kenji López-Alt, managing culinary director of Serious Eats, wrote a piece detailing the myths. He tells us the truth.

Truth 1: Cast iron is not that difficult to maintain

Noelle Carter: Cast iron is popular. While it has a lot of fans in the food world, it can be mysterious and intimidating. One of the biggest things I hear about cast iron is that it's difficult to maintain.

J. Kenji López-Alt Photo: Peter Tannenbaum

J. Kenji López-Alt: That is a myth you hear often. The issue that comes up with it is maintaining the seasoning, which is the layer of polymers that form when you heat oil in it. That's what gives the cast-iron pan its nonstick properties and what makes it such a good surface for cooking on. But even that layer of seasoning is way, way easier to both form and to maintain than a lot of people make it out to be.

Truth 2: Cast iron does NOT heat as evenly as you've heard

NC: Cast iron has this reputation for heating well and evenly and for being a great conductor of heat. But that's not true.

JKLA: No, that's actually one of the big myths about it. The way you measure how evenly something heats is by its thermal conductance. Out of the materials that we cook with, cast iron has very, very low thermal conductance. That means when you place it over a burner, it's going to get hot spots and cool spots very quickly because heat doesn't travel from one area of it to another very efficiently.

The good thing about cast iron is that it's so dense and so heavy that it's able to retain a lot of heat energy. Which means that when you put something like a steak in it, the pan is not going to cool down very fast; it's going to give you that nice sear. But in order to get the entire pan heated evenly, you have to heat it over a relatively long period of time. You have to make sure you rotate it on the stovetop. Or better yet, heat it in the oven so that you get a really nice even heat on it.

Truth 3: There is a difference between old and new cast iron

NC: One of the things that I hear is that there's a difference between old cast iron and new cast iron. There are the pans that you may have inherited from your grandmother or you find at a flea market, and then there are the pans that you can find pre-seasoned at the store. Is there any difference between new and old cast iron?

JKLA: There actually is. New cast iron will work just fine. But if you take a new cast-iron pan and an older cast-iron pan and compare them side by side, the first thing that you're going to notice is that the new cast-iron pan has a pebbly surface to it.

That's because cast iron is cast in molds made out of sand. Once they come out of those molds, they still have that sandy texture. In the old days, they used to take those pans and then subsequently polish them so that the surface would end up being completely smooth and flat. With modern pans they skip that step -- I think, mostly as a cost-saving maneuver.

You'll find that, performance-wise, modern cast iron will work just fine, but it never gets quite as nonstick or quite as well-seasoned as older cast-iron pans do. That's just because of the texture of that surface.

NC: Let's say I'm at a garage sale and I run across a really-good-looking cast-iron pan. Is there anything I should look for before I buy it?

JKLA: Vintage pans can be 100 years old, and they've been stored in many different ways. If you can find a pan that is polished, smooth, shiny, and has that nice satiny luster to it -- that obviously somebody has already taken the time to clean it and season it for you -- then you're really lucky. Most likely, they're going to charge you a lot of money for that because the type of people who do that know what they're dealing with.

If, on the other hand, you find a pan that has some kind of tarnishing or rust, often those pans are still quite good.

What you really want to look for is any kind of pitting or warping in the metal because older cast iron was a little bit thinner than modern cast iron. With repeated use they could get warped; they sag in the bottom, bulge out or sometimes even crack. If they were stored improperly for a very long period of time, then they'll get some kind of pitting. You'll see that as little holes, little dimples in the metal. If it has either of those defects, then you want to pass on it.

But if it's just a surface discoloration, rust or maybe uneven seasoning that's chipping off, then those types of pans you can restore yourself, if you're willing to put a little bit of work into it.

Truth 4: It's OK to cook acidic foods in cast iron

NC: Can I cook acidic foods in cast iron? Can I make a tomato sauce in my cast-iron pan?

JKLA: The general idea is that acidic foods will both take on flavors of the iron, and they'll also wreck your seasoning so that you'll have to start seasoning your pan over again. But this is actually not the case.

The seasoning is pretty tough. It's a polymer -- it's basically related to plastic -- that ends up filling in the little gaps and holes on the bottom of your pan, giving you a smooth surface. As long as you've formed it properly, that polymer is quite hard. Cooking acidic foods in it will not really strip that, at least given reasonable cooking times.

I wouldn't recommend cast iron as a pan to cook a 6-hour-long tomato sauce in. But if you're going to sear a steak or a chicken breast and then you want to make a quick pan sauce, you can do that just fine. I cook with wine, I cook with tomatoes in it all the time. My pan has come out the other end perfectly seasoned.

NC: When it comes to seasoning, people seem to have religious convictions about what fat they use. Some people prefer bacon fat, some people prefer lard or oil. I've read a lot recently about flaxseed oil.

JKLA: I think there is one famous article online about using flaxseed oil. My experience with it is it does build up seasoning faster, but it also builds a more brittle seasoning that's more likely to come out of the pan.

I honestly would say that there is not really any best fat. The best way to season it is just to cook in it repeatedly. Whatever fat you're going to use to cook in, that should be the fat that you're seasoning it in, just because it means that you're more likely to do it. I keep canola oil and olive oil on my countertop, so those are the fats I cook with most.

Truth 5: You can wash your cast-iron pan with soap

JKLA: Every time I use my cast-iron pan, as soon as I'm done with it, I just give it a quick wipe out. You can clean it in the sink. I put soap on mine. Soap will get rid of oil but it won't break down that seasoning. Rinse it and put it back on the stovetop. You don't want it to sit wet because that will cause it to rust. Once you're done cleaning it, you just throw it back on a burner. Let that excess moisture cook out until the pan is a little bit hot. Then just rub a thin layer of oil into it with a paper towel.

I think one of the reasons cast iron is so intimidating to people is because of the seasoning step. Once you just make it part of your daily routine, it's an easy 10-second step to do at the end of every cooking session.

Cooking in cast iron

López-Alt's recipe: Foolproof Pan Pizza Photo: J. Kenji López-Alt

NC: Do you have any favorite dishes you like to cook in cast iron?

JKLA: Absolutely. Cast iron is a super versatile thing.

It's great for meat. If I'm cooking indoors, I can't think of a better way to cook a steak because it can retain such a high amount of heat energy. You place a steak in there, you get a better sear than you get out of anything.

I roast whole chickens in it. It's great because it can go straight from the stove top to the oven.

I make bread and pizza in mine. One recipe I have that I really enjoy is a no-knead pizza. You basically mix together the dough and then just dump it into the cast-iron pan that has a little bit of olive oil in it. Then you just let the dough sit there and it fills up the pan to the edges and rises a little bit. Then you just top it and throw it in the oven. It comes out like a deep-dish pan pizza with really crispy, almost fried-in-olive-oil-focaccia-type edges.

Cast iron is great for baking pizza, baking focaccia, baking pull-apart rolls, corn bread, anything that you really want to get a nice crust on. If you're looking for brown and crispy, then the cast-iron pan is a great way to get there.

[Over at Serious Eats, López-Alt compares cast iron to nonstick surfaces and discusses the use of metal utensils. Read the whole thing.]

Previously: Bay leaves are an optional ingredient, 'but things are definitely better with them'