Material Stories: what is cast iron?

Cast iron: it’s a heavy-duty cooking material, with a host of unique properties. Cast iron pans might bring to mind black iron skillets, or perhaps colourful Le Creuset dutch ovens. But what exactly is cast iron? And why would you choose to cook in such a weighty, and often high-maintenance piece of cookware - instead of a lighter non-stick or stainless steel pan?

Cast iron may have a reputation for being hefty and old-fashioned, but it’s had a resurgence in recent years. Its versatility and heat retention make cast iron pans true kitchen workhorses, with properties that make them a pleasure to cook on too.

For the third instalment of our Materials Stories series, we’re going to take a deep dive into this extraordinary material. We’ll explore how cast iron pans are made, how to cook with and clean them, and how they differ from other types of pans. Let’s get into it.

How is cast iron made?

Cast iron differs from other types of iron in that it has a high carbon content (2% or more), giving it a relatively low melting point. This allows the iron to be melted down and cast into a mould, which is usually made of sand. After the iron has been cast, the resulting metal shape is removed, and the sand can be crumbled and reused. 

These sand moulds are what gives cast iron products a characteristically rough-textured finish. Cast iron isn’t just used for pots and pans, either - you may have also seen ornate cast iron fences, old-fashioned radiators, postboxes, pipes and gutters. 

Cast iron is very durable, but it’s a relatively brittle metal. A cast iron skillet can be decades old and still work perfectly - but if it gets dropped or subjected to thermal shock, it may crack. This is why cast iron pans are so thick and heavy. If they were thin, they’d be very fragile.

What are the benefits of cooking on cast iron?

Cast iron pans are famously good at searing food: think golden, crispy potatoes, perfectly crusted steaks and blistered vegetables. The material can withstand and maintain very high cooking temperatures, which makes it the perfect choice for high heat cooking. 

The iron also radiates a lot of heat outwards, so as well as cooking the food directly in contact with the pan’s surface, it’s cooking some of the food above it too. This is perfect for getting your food cooked all the way through before it burns, such as chicken thighs or potatoes.

Cast iron is also great at cooking food over a long period of time (think braised meats and stews), thanks to its excellent heat retention. This all means a cast iron pan allows you to sear a piece of meat over a high heat, then set it to braise low and slow in liquid to become fall-apart tender - all in one pan.

And finally, did you know that cast iron becomes naturally non-stick over time? Here’s how…

What is ‘seasoned’ iron?

When you see people talk about seasoning their cast iron, they’re not referring to salt and pepper, and the process won’t impart any flavour into your food. It simply means building up layers of cooked-on oil. This coating gives the pan non-stick properties, and also protects it from rust. 

Seasoning constantly develops the more you cook, improving your cast iron pan’s non-stick surface over time. Bare cast iron is grey in colour, but as the seasoning builds, it will turn black and shiny. Just think of how a well-used baking tray turns brown, and then black with burnt-on grease.

Read: 10 common myths about cast iron pans

How do you season a cast iron pan?

Seasoning basically just involves applying some kind of fat to the pan and heating it up to smoking point. This polymerises the oil, turning it into a hard, plastic-like layer. Many people swear by certain types of oil, or even lard - but normal rapeseed (vegetable) oil works just fine.

The key to good seasoning is building it up in super thin layers, which means wiping on oil and then wiping it off with a paper towel before you heat the pan. First, do a base coat of seasoning over the entire pan to protect it from rust - you can bake the whole pan in the oven for one to two hours. Then, boost the non-stick by seasoning just the cooking surface a few times. This can be done on the stovetop.

We wrote an in-depth guide to seasoning our Solidteknics iron pans here - but you can use this method for seasoning any cast iron pan too (unless it has a wooden handle, in which case season it on the hob only). We also have a quick video on it here too.

How do you cook on cast iron?

Compared to pans made of other materials, cooking on cast iron is a very different experience. Cast iron isn’t very conductive, so it takes a while to heat up. Before you add any food, you should preheat your pan on a low to medium heat for several minutes. This lets the heat gradually spread through the whole pan, ensuring even cooking without hotspots.

Cast iron may be slow to heat, but it holds heat very well - so heat can build and build with patient preheating. To achieve the perfect sear, preheat for 5-10 minutes. Then, add your food and resist the urge to move it around. Allowing food to cook untouched will help achieve a beautiful brown crust.

Cast iron cookware is also oven safe, meaning you can sear food on the stovetop before finishing it off in the oven. This is especially good for cooking meats, such as large roasting joints, extra-thick steaks and spatchcocked chicken.

You may have heard that you shouldn’t cook acidic foods in a cast iron pan, such as tomatoes or wine. However, a small amount will be perfectly fine, especially if you have a well-developed layer of seasoning.

How do you clean cast iron?

There are a lot of misconceptions about how you should clean cast iron, the main one being that you shouldn’t use soap in case it damages your seasoning. However, seasoning is baked on oil, and doesn’t wash away easily. As long as you’re not scrubbing with steel wool, it’s perfectly fine to use soap when washing your cast iron. 

For best results, wash your cast iron soon after cooking so that you don’t have to scrub it too much. Avoid soaking your cast iron, and never place it in a dishwasher - unless you want a rusty pan. For the same reason, you should dry your cast iron pan immediately after you’ve washed it.

What is enamelled cast iron?

You may have wondered - if Le Creuset pans are made of cast iron, why don’t you have to season them or worry about rust? This is because they’re enamelled: in other words, coated with a ceramic glaze.

This enamel, as well as giving your cookware any number of bright colours, protects the cast iron underneath from rusting. It’s also easy to clean. However, enamel doesn’t build up seasoning, and so can’t achieve the same non-stick properties as a bare iron pan. Plus, they tend to be much more expensive.

Enamelled cast iron is often found in the form of lidded cast iron casserole dishes, because they’re perfect for cooking dishes like stews and braises. The enamel prevents traces of iron from leaching into the food during the long cooking time.

What’s the difference between cast iron and wrought iron?

If you’ve had your eye on any of our Solidteknics pans, you may have noticed they’re not actually made of cast iron, but wrought iron. Instead of being poured into a mould like cast iron, wrought iron is instead heated and then worked with tools to achieve the final shape.

Wrought iron has very low carbon content, which makes it stronger than cast iron. As a result, Solidteknics pans are much thinner and therefore lighter than their cast iron equivalents - but they’re even stronger.

However, cooking on a Solidteknics pan feels very similar to cooking on a traditional iron skillet. They need to be seasoned, preheated and washed in the same way, whilst being excellent at searing food. Ours come either with a light pre-seasoning, or fully pre-seasoned so that you can cook straight away. Considering a Solidteknics pan? Here’s what you need to know.

Feeling inspired? Check out our full collection of cast iron pans here, or our entire cast iron collection here (think roasting dishes and pepper grinders too).

Or, take a look at our thinner, lighter Solidteknics wrought iron collection.

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