Properties of Cast Iron

Ordinary lightweight pots and pans have their uses in the kitchen, but they'll never become family heirlooms. Cast iron pans are different. They can last decades or even generations, and instead of wearing out, they'll actually become better the more you use them. That may sound strange, but it's true — and it's all because of cast iron's properties.

There are many kinds of iron and steel, and they have a few broad differences. Steel, on the whole, is stronger and lighter. It's also not as brittle as cast iron, which means it's less likely to break as the result of a sharp impact. One chief reason for that is cast iron's carbon content. Cast iron typically contains 2 to 4 percent carbon, and it can go as high as 6 percent. Steel typically contains less than 1 percent.

Another important thing to understand about cast iron is that it isn't wrought, or worked. Those two types of iron are made through different processes and have different virtues. Wrought iron is heated to a higher temperature, as high as 2,900 degrees Fahrenheit, and then hammered into whatever shape is needed. The extra heating and hammering drive out some of the impurities from the iron, leaving it stronger and harder. Casting iron is done by heating the iron until it melts — at around 2,100 or 2,200 degrees F — and then pouring it into a mold.

Wrought iron is better for some jobs, but it wouldn't be a practical way to make pots and pans. Hammering out the shapes and joining the edges to become watertight would be costly and time consuming. Because cast iron uses a mold, it can be shaped into a shallow skillet, a ribbed cornbread pan, a deep Dutch oven or even a tea kettle with equal ease. More importantly, though, cast iron's properties make it an excellent cooking material.

Aluminum and copper are great metals for cooking, because they heat quickly and conduct heat very efficiently. Cast iron is an ideal metal for cooking for exactly the opposite reason. Cast iron takes a long time to heat, but once it's heated, it holds onto its heat like few other materials. That's good news for cooks, because it means your pan won't cool down as soon as you put your food into it. It's a problem with lightweight pans and why chefs prefer to use cast iron to put a seriously seared crust on meats or fish.

Some fans of cast iron will tell you they love it because it heats so evenly, but that's not entirely accurate. The areas of the pan over your flame or electric coil will heat quickly, but that heat will only spread slowly to the rest of the pan. To get it heated evenly, you'll need to move the pan around the burner or else preheat it in your oven for 20 to 30 minutes before you use it. Once the heat does get distributed evenly throughout the pan, it'll stay evenly heated as long as you keep using it.

A slab of bare cast iron wouldn't work well as a cooking surface. It would react chemically with your foods to discolor them, it would be terribly susceptible to rust, and your foods would stick to the surface like glue. Preparing your pans for use, or seasoning them, is an essential preliminary step before they become functional cookware. Modern cast iron generally comes preseasoned, but it's still worth taking a moment to understand how the process works.

Seasoning essentially means bonding a thin layer of oil to the bare metal of your pot or pan. At high temperature, the oil's molecules break down and reform with a different chemical structure, a process called polymerization. It turns the oil into a ridiculously tough, slippery surface that's physically bonded to the metal. If you've ever tried to scrub the dark stains of cooked-on oil from a pan, you know exactly how tough it is and how stubbornly it sticks to the metal. Seasoning a cast iron pan means simply harnessing that process and making it do what you want.

To season a cast iron pot or pan, first, coat it with the thinnest possible layer of oil. Serious hobbyists can debate for hours over the merits of flaxseed oil, rice bran oil and other exotic options, but any fat will work. Your great-grandparents probably just used lard or bacon fat, for example. Heat the pan until the oil reaches its smoke point, wipe out any excess, and set it aside to cool. You can do this on your stovetop or heat the pan in your oven or on your grill in the backyard for more even heating. It's a smoky job, so you can certainly make a case for doing it outdoors.

Repeat the process as many times as you like, from three or four to 10 or more, until you have a smooth, even, faintly glossy surface on the inside of your pan. At that point it's ready to use. A preseasoned pan can be used as soon as you buy it, but adding an extra layer or two of seasoning certainly helps.

When you start using your newly seasoned pan, it's best to stick to frying things for the first few uses. Always heat the pan thoroughly before you add any oil or food to it, because food will stick to a cold pan. Cast iron throws off a lot of heat, so if you hold your hand over the pan, it's easy to judge when it's hot enough. If you add your oil or fat to a heated pan and follow that with the food, it should cook with minimal sticking.

Cast iron is especially good for cooking at high temperatures. The instructions for non-stick pans often tell you not to heat them to high temperatures when they're empty because it could damage the pan or its coating. Damaging a cast iron pan, on the other hand, isn't an issue – the melting point of cast iron is around 2,100 degrees F, much higher than any actual cooking temperature. And that heat will only improve your seasoning.

Some hobbyists go on at length about all the do's and don'ts of cast iron, making it sound complicated and high maintenance. That actually says a lot about the human need to have something to fuss over, but relatively little about cast iron. In truth, you can use it fearlessly, because that tough coat of seasoning will stand up to a lot of abuse. Feel free to use metal utensils, for example, because unless you're actually trying to gouge chips out of the seasoning, you'll probably never damage it.

You can also cook acidic ingredients in a cast iron pan, whether that means adding vinegar to a pan sauce or simmering meatballs in tomato sauce in your cast iron Dutch oven. Take only one precaution: Leave the acidic ingredients in the pan once they're cooked, and clean the pot or pan as soon as possible after cooking.

You can get a hot reaction on your social media feeds if you mention cleaning your cast iron with soap and water, but — again — there's no reason not to. It's an effective cleaning method, after all. Just don't scrub at it with metal scouring pads, and don't let water sit in the pan under any circumstances. If food is tough and stuck on, put the pan back on the stovetop with a bit of water in it and bring it to a boil. As the food softens and loosens, scrape away at it with a wooden spoon or nylon spatula until it comes loose.

If you really don't want to wash your pan, clean it chef-style. Heat the pan with a little bit of oil, and pour in a handful or two of coarse salt. Fold up a clean kitchen towel to protect your hand, and then use the towel to scour the pan with the salt until you've removed any remaining food debris. Don't dump the hot salt straight into your trash, or it might melt the bag. Whether you clean your pan with water or salt, you should always heat it after cleaning to make sure it's thoroughly dried. Then, rub it lightly with a coat of oil to protect the surface. Once it's cool, you can put it away for the next meal.