How to Season Cast Iron Cookware

Seasoning is the black patina that builds up on your cast iron skillet with regular use, a non-stick surface that’s slick enough for eggs to skate across the pan, but tough enough to withstand the blazing heat needed to properly sear a steak. It’s the at-home work you do to turn a cast iron pan into an heirloom, and it’s as important for your cooking as the iron your pan is made from.

There’s a lot of advice on the internet about seasoning and cast iron care, and a lot of misinformation as well, so we want to set the record straight on what you really need to know to season a cast iron skillet correctly. We’ve spent years obsessing over how to make the best cast iron pan, which means we’ve devoted hundreds of hours to researching and comparing different ways to season it. That’s included testing a wide range of oils, heat ranges, and techniques while consulting chemists, machinists, and cast iron lovers around the country.

When subjected to high heat, long chains of fat molecules break down into short-chain polymers that bond with naturally produced carbon and bare iron, forming a kind of glaze. This is seasoning, and it has smooth, non-stick properties similar to Teflon. It also forms a natural barrier between the air and the naked iron in your pan, acting as the first line of defense against rust.

If you put cast iron under a microscope, you’ll see that its surface is bumpy and porous, and those bumps and pores expand once the pan is heated. Seasoning, especially in the early life of a pan, bakes right into the iron, filling in those pores and smoothing everything out into an even surface. Over time, as layer after layer of seasoning builds up, the cooking surface eventually becomes pure seasoning, securely bonded to the iron underneath.

Seasoning Cast Iron in the Oven

Seasoning a pan—as a verb—adds a thicker, more thorough coat of seasoning all over the entire pan, all at once. It’s a way to kickstart the seasoning process and build a base layer that will grow stronger every time you cook with your pan.

Some cast iron owners do this for every new piece of cookware they get, and then repeat the process every few months or years; others never bother, opting for a slow and steady “keep cooking” policy. Field Skillets are well-suited for either method. Our preferred method: cook with your skillet often, and apply Field Seasoning Oil after every use.

After testing every technique out there, we’ve developed an approach based on gradually boosting the temperature of the pan to bake the seasoning into the surface, not just on top of it. Your ideal seasoning temperature is just below the smoke point of your oil, the point where it breaks down into carbon and short-chain polymers that can bond with iron. Below that point for too short a time, and the oil won’t fully polymerize; above that point for too long, and the oil runs the risk of skipping past the polymer stage and straight into completely burnt carbon.

The best oils for cast iron seasoning

The best fat polymerization comes from oils rich in polyunsaturated fatty acids—the compounds that give ‘drying oils’ the ability to thicken and harden once exposed to air. After testing dozens of seasoning methods with all kinds of fats, our favorites are organic grapeseed oil and sunflower oil — Field Seasoning Oil uses both. These oils break down into tough but thin coats of seasoning that build well on each other over time.

Saturated fats like lard and coconut oil aren’t the best choice for oven-seasoning; as they break down, they don’t open sufficient bonding points for carbon molecules to adhere to the molten polymers. On the flipside, beware of drying oils that are very high in unsaturated fatty acids, such as flaxseed oil. While flaxseed oil is a popular choice on the internet, we’ve found the seasoning it produces can be brittle and prone to flaking. Grapeseed strikes a good balance, is easy to find in most supermarkets, and it’s also a great everyday cooking fat.

Do I Need to Season a Pre-Seasoned Skillet?

These days, most cast iron manufacturers pre-season skillets, us included. You can cook with these pans right out of the box, but they won’t actually be totally non-stick. The Field Skillet, which comes coated with three seasoned layers of grapeseed oil, is actually less pre-seasoned than other producers, because we focus on baking seasoning into the pan, not on top of it. But we’ve found this approach develops better subsequent layers of seasoning over time, compared to other pans that try and speed up the process by covering up the iron with a more cosmetic top coat.

You don’t have to oven-season a Field Skillet, or any pre-seasoned cast iron pan; whether you want to is up to you. Early in the lifetime of your pan, some proteins like bacon and eggs may stick a bit. This is fine, and all part of the gradual seasoning process — and our Seasoning Oil is engineered to help. The most important thing to do is cook with it often, and to follow these guidelines over the first 15 to 20 sessions with your pan:

Cook with fatty foods, and be generous with butter and cooking oil

A couple tablespoons of oil or a good hunk of butter will keep everything well lubricated while pan-frying or sauteing. (Don’t be afraid to add more!) You can use any fat you like, though if you want to cook with seasoning specifically in mind, you can stick to grapeseed at the beginning.

Keep the heat low

In the early life of a pre-seasoned pan, even one you’ve oven-seasoned yourself, your food may stick a bit. Keep the heat to low or medium as you build up your initial layers of seasoning; caramelizing onions, frying chicken, and baking cornbread are all great starter dishes. Once you’ve broken your pan in, you can let the pan take more abuse.

Avoid acidic and long-simmered foods

Tomatoes, wine, citrus, and vinegar can eat away at seasoning, so keep the tomato sauce out and avoid deglazing for now. A lightly seasoned cast iron pan may even add unpleasant ferrous flavors to acidic foods. Once you’ve completed the breaking-in stage and seasoning is producing reliable non-stick performance, a little acid here and there isn’t a problem.

Great cast iron seasoning — and patina — comes from time and use. If you cook with your Field Skillet regularly, you will steadily develop a beautiful non-stick cooking surface.