All About Cast Iron Cookware

Beatriz oiling a cast iron skillet

I’m Beatriz Garcia.  I’ve researched cast iron cookware extensively – so that you don’t have to.  Read this guide which draws on my own experience as well as the theory; and you’ll always know how to treat your iron.

How To Season Cast Iron Cookware

If you know what you're doing, and want a quick reminder:
  1. Wash and dry your pan
  2. Warm in oven
  3. Apply a super-thin layer of oil (ideally flaxseed)
  4. Heat the pan until it smokes
  5. Repeat 3- 5 times
Do please read on for some of the important details

When I first started using cast iron I couldn’t be bothered with all the seasoning. Plus it came pre seasoned so there was no need – right?

I didn’t realize that scraping all the food off the pan was actually more work than seasoning it would have been.

Now I save my time and season it when I get it.

Before I explain how to do this please bear in mind: Seasoning Cast Iron and seasoning Carbon Steel is the same thing. These two materials are very similar. There’s no point going into the differences as from a maintenance and care point of view – they are identical.

When to season

Most cast iron comes pre seasoned, with carbon steel this is less likely. Seasoning by the manufacturer is not meant to be the final layer. It’s always worth topping up yourself.

When I season cast iron

  • When I get a new pan (even if “preseasoned”)
  • If I ever use detergent to clean it, or it accidentally ends up in the dishwasher
  • If I see it’s starting to get sticky
  • If the color starts to dull, or it starts to look rusty

One thing I don’t do is season every time I use it. For me this starts to become too much work and I’m not sure it’s necessary.

Testing the seasoning

How many times should you season, do you need to season it again? If you’re not sure, why not test it? This applies at any point. If you think you’ve finished the seasoning process – test it. If you’re not sure if you should reseason – test it.

Here’s how to test it:

  • Add some oil to the pan. Spread it around the inside of the pan
  • Warm up the pan on a low to medium heat for 3 – 5 minutes. The oil should be gently sizzling or bubbling, not smoking.
  • Add an egg and cook it

If the egg sticks to the pan then it needs more seasoning. Remember this isn’t Teflon. the egg may stick a little, but it should be easy to rinse it off.

3 eggs in a cast iron skillet

Note the steps here. Many people stick an egg in the pan without oil or preheating then complain it is sticky. Even Teflon is sticky under those circumstances!

Preparing the pan

If the pan comes covered in oil this is almost certainly not food grade oil (which could go rancid) but machine oil. You need to thoroughly strip the oil off before seasoning. You don’t want this stuff in your food.

If the pan comes pre seasoned you may want to think about whether to strip this layer of seasoning off first. I don’t, but if your family has food allergies or intolerances it may be a good idea. This video explains the idea well, as well as the seasoning process:

Sanding down your Cast Iron Cookware

I’ll be straight with you – I’ve never done this. I don’t recommend it. Manufacturers normally don’t recommend it. Why would you do it? Here’s why some people consider it:

  • Even new cast iron can come a bit coarse, especially if it’s lower quality
  • If it’s been mistreated it might also have a rough surface
  • Even if smooth it could be a little deformed or warped

Is it important for it to be smooth? Well a smoother surface might help make the pan more nonstick.

If you are going to do it, please do it on a cheap pan or an old one. There’s a lot of approaches out there, some people even do it by hand! Sounds like a good way to waste time to me. If I were to do it I would probably do it with a machine, the way this guy has:

Be aware – he is removing the seasoning as well as sanding it down. Before sanding you could consider just removing the seasoning to see what it’s like.

Which Oil To Use in Seasoning

There are lots of different recommendations on which oil to use for seasoning. Absent any hard evidence, it’s hard to know which is best.

I think there are three things more important than the type of oil anyway:

  • The oil must be pure. Check the ingredients – if it isn’t a single pure oil – don’t use it. This is because any other ingredients are impurities that will get baked into your seasoning layer. This will weaken it and make it easier to chip. This means spray oil is a bad idea for example. Organic oil is less likely to have additives, but check the ingredients.
  • Check the smoke point of the oil using this guide. Unlike for cooking, you will need to heat the oil beyond its smoke point. This means the smoke point of the oil must be low enough that you can reach it.
  • Use a food grade oil. I’m sure you can get cheap machine oils from a hardware store that work great. That would be a bad idea!

Given these, what oils would I recommend? I’ll give you three recommendations by three different sources:

A Jar of Oil With A Dropper For Seasoning Cast Iron

I liked the flaxseed oil recommendation. I also think that Sheryl explained well why some people found flaxseed didn’t work (the version they used had additives). I use flaxseed oil normally, but if I’m out I use canola oil (also called rapeseed oil).

An Easy To Understand Explanation Of The Science Of Seasoning

If you don’t care about the science, part feel free to skip this section. You won’t lose anything: I wrote it for those who are curious.

The idea

The idea is to form a thin slippery coating over the cast iron. This coating needs to be food safe, and durable. It also needs to bond to the cast iron.

Think of how nothing sticks to a smooth plastic surface (like tupperware). This is the effect we want.

Did you know that a lot of plastic is made from crude oil? We need to get food oils to have a similar effect.

How a plastic is formed

This is done by heating the oil to a high temperature, beyond its smoke point. If you were cooking this could be dangerous as the oil starts to break down. In this case it is exactly what we want! By breaking down the oil, it can then reform into polymers. This process is helped by the presence of iron. The polymers bond to the iron or each other and form a plastic layer.

Sheryl Canter explains this in more detail.

The Seasoning itself

Thin Layers

The first thing to remember is that you must season in as thin a layer as possible. Big layers don’t work well and tend to chip off. Think of a single fat layer of paint instead of many thin coats, which is better?

I’ll repeat this a few times without embarrassment: several thin layers is much better than one thick layer.

Prepare the Oil

If the oil is in the fridge or pantry, take it out. It needs to warm up, at least to room temperature. The colder it is, the more viscous (thick) it is. Viscous oil doesn’t spread as well and you end up with a thicker layer. Remember – we want a thin layer!

Prepare the pan

Now wash the pan. I recommend gently washing it with warm soapy water.

At this point you need to watch out for manufacturer’s oil. If your new pan is dirty and / or oily then it probably has machine oil on it. The oil protects the pan from moisture during transit. This oil is not seasoning and is more common on carbon steel. The oil is also not food safe. You need to completely remove this oil. Scrub extra hard until it’s all gone.

Rinse well to remove any soap or detergent off the pan.

Dry and Heat

Dry off any water with a towel. Once it’s dry you need to heat it up. It’s easiest to heat it in the oven at this point.

At this point you are heating it up to:

An oven - ideal for drying cast iron cookware

I would suggest heating it to 200℃ (400℉) for half an hour. This isn’t an exact science though.

Applying the oil

Let your pan cool down a bit so it is still hot, but not too hot to touch. 

Apply the oil with a paper towel. Apply it as thinly as you can, then get another paper towel to wipe it all off. A thin layer will still remain, which is all you need.

The oil needs to be applied to the whole pan. This includes the handle and the bottom of the pan. Anything that is cast iron should be covered in oil.

Some articles suggest baking the pan in the oven with aluminium foil underneath to catch the dripping oil. If you need to catch dripping oil you have too much oil on. Don’t do this.

Heating the pan

Whichever way you heat the pan, you must exceed the smoke point of the oil you’ve chosen. This means it will get smokey, so do it outside, or open the windows in the kitchen.

You can heat it in the oven, or over the grill. You know it’s working when it smokes! I don’t see anyway around this unfortunately. You need the oil to break down so it bonds with itself and the iron. This happens when it smokes.

When I first did this I set off the fire alarm in the house as I hadn’t closed the kitchen door. Close the door, leave the windows open, and the smoke will quickly disappear.

Make sure you carefully monitor it – smoking oil is the right temperature, so don’t go hotter. Oils also have flash points (when they catch fire), and you want to avoid this.

Number of times to do this

The idea is to repeat this a few times to build up a nice seasoning made of a few coatings. There are many factors affecting how many times you should do it. It will depend on the level of preseasoning, if this is the first time, and the pan itself. I would suggest doing this until the pan is nonstick (see test above). If you want a number, try these:

  • 5 times if not preseasoned
  • 3 times if preseason
  • 1 time if this is a “top up”

Another, quicker, test is that the coating should be shiny. Perhaps repeat until it is shiny, and then do the nonstick test (above).

Auto Seasoning

Field Company, and others, recommend auto seasoning. The idea of this is that the pan will season itself by cooking with fats and oils. It will build up a small layers each time you cook.

Seasoned Cast Iron Pan With Food In It

Honestly, I don’t know if this is true, but I am skeptical. The reason is that you need to reach the smoke point of the oil for the seasoning to work. Smoking oil when cooking is a bad thing to do. The healthy oil breaks down into not so healthy compounds. Instead of sticking to the iron pan it sticks to your food and you eat it.

You should use oil or fats when cooking with cast iron anyway, I even use a little with nonstick. I can’t say for sure if it is adding anything or not to the seasoning, but I doubt it.

If you see an extra layer of black after cooking, this is probably burnt food / carbon, not seasoning. I would recommend cooking at a lower temperature.

Summary

So in summary:

  • Season your pan with pure oil at least once
  • Keep your pans dry
    • Before seasoning
    • After seasoning
    • During seasoning
    • When not seasoning
    • All the time actually, unless actually cooking or washing them
  • Use as little oil as possible when seasoning
  • Smoking oils is good when you are seasoning and bad when you are cooking

If you get it right, caring for cast iron can be good fun. And it you get it wrong, don’t worry, it’s probably fixable:

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