cast iron seasoning

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How do I know when I need to re-season a cast iron pan?

You get a new pan from the store, or an old, new-to-you pan from a family member, and the first thing you’re likely to do is spend some time re-seasoning. Fresh from the factory, or stale from neglect, obviously is a great time to put in the effort.

But what about the pans you already own and are using regularly? How do you know if they need some intensive cast iron care or even a full seasoning restart?

I was cooking a batch of buttermilk pancakes this morning and noticed a chip on my twenty inch grill, the same pan that had given me some trouble a couple months back (but in a different spot on the pan!) That blemish had likewise started as a small chip and I’d let it fester for a few months only to watch it grow from a dime-sized divot into a scar that rendered a quarter of the large pan basically useless.

Now this new pit has me pondering my pan options: to push through, spot-repair, or fully re-season?

So, how do you know when it’s time to start the re-seasoning process?

It’s Wearing Out

Seasoning is just layers and layers of carbon built up over time and effort. Maybe those layers are just getting old, or thinning out in various places. Maybe you’ve been cooking too many delicious tomato sauce-based recipes and the acid and lack of fresh oil is leaving those layers a bit lacklustre. Or maybe you’ve built up so many layers that the actual shape of your pan is starting to change. Seasoning does get old and wear out, and a once-amazing pan might just need a refresh.

It’s Chipping Off

Like my morning dilemma, sometimes you pull a pan from the shelf and either from rough use or being bumped in the cupboard, a bit of the seasoning has actually cracked and chipped away. This creates an unwelcome uneven surface and over time is simply going to get bigger and rougher and make your pan less useful. A full re-seasoning on a big chip or a chip in the main part of the pan is probably the best course, but try a spot re-seasoning first. Scrub the spot down with some steel wool or an abrasive sandpaper, then re-season like it’s a new pan. If that doesn’t work, strip the whole piece to bare metal and start fresh. Plus, you don’t want any of those stray seasoning chips mixed in with your morning hashbrowns.

It’s Rusting Up

The worst cast cast iron scenario is rust. Stored wet, or maybe having been through a long cold winter (accidentally, I swear) left inside the barbecue, rust damages the iron at a molecular level and loosens your seasoning. Also, it tastes awful with eggs. A full cleaning and do-over is probably the best way to get back on the right foot with a pan that’s got a case of rust.

Most of all, you’ll likely just know when you need to re-season. A well-seasoned pan is a great tool. A pan that needs some care and attention from years of use, wear and tear is just …less so.

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How long does it take to season a cast iron pan?

Probably one of the most well-known bits of cast iron lore is that the more that you use your pan the better it will get.

This rule of thumb is referring to the seasoning, the thin, black layers of polymerized oil that have been converted to this state by heat and have adhered to the surface of the pan creating that famous non-stick state of cooking bliss.

Pre-seasoned pans from the factory are sold with a few layers of seasoning applied shortly after manufacture, and for many this is “good enough” to start cooking with your new pan even as you peel the labels off. But for others, a fully seasoned pan takes work, and adequate seasoning is a matter of opinion and personal evaluation. To them, no pan ever comes from the store with enough seasoning to be considered fully ready to cook on.

The most unhelpful advice I’ve ever read on seasoning basically says that a pan is fully seasoned when you know that it is fully seasoned.

What those folks are getting at is simply that it will feel like it cooks better. Or it will pass some kind of non-stick test. You’ll just know… y’know?

A test, you say? For example, some swear that a pan is only seasoned when it passes the egg test: crack an egg into the center of a hot pan, cook it to doneness, then slide it onto a plate… all of this without using a spatula or any other cooking tool. If it slides into the plate and leaves a clean pan behind: voila! Your pan is perfectly seasoned. If it sticks then get back to work: you’re not there yet.

But no, you insist, really… how long does it take to season a cast iron pan?

In my experience, it takes however long it takes to build up five … ten … twenty solid layers of seasoning. You’ll just know… y’know?

That might take just one quiet afternoon with a hot oven, some oil and a bit of elbow grease.

Perhaps a full weekend out camping and cooking all your meals over a fire where the hot flames meld oil to iron will find your pan seasoned perfectly.

Sometimes a couple months of casual cooking at home is required as you notice week by week that your pan gets a little smoother and easier to use each time you fry.

Or occasionally it will take years of waking up early to prepare delicious Saturday breakfasts for your still-sleeping kids until you realize that your seasoning should be considered a family heirloom.

So maybe those folks with the unhelpful advice are right. A pan is fully seasoned when you know that it is fully seasoned. You’ll just know… y’know?

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Can I use a cast iron pot or pan to boil water?

One of the adages of cast iron cooking is that to improve your cast iron cookware, just use it.

What is not necessarily clear in that basic advice is that to make any cast iron seasoning better, stronger, and more resilient, the use of your cast iron should follow a couple basic principles about how it should be used. Simply:

Heat and oils are good in that they improve your seasoning.

Soaps and acids are bad in that they degrade your seasoning.

So, where does water fit into these rules? And what do we mean by boiling water?

A small bottle of water sits in the middle of a cast iron frying pan.

For example, a lot of recipes call for a portion of water (or broth or wine or other neutral liquid) and instruct bringing it to a boil. Is this bad for the pan?

Or, when I first started using my cast iron dutch oven I was unclear on if I could use it to, say, cook up a big pot of pasta or if I should stick with the steel pot we’d been using for years.

I did a lot of reading on this a number of years ago and the best advice anyone gave me on this topic is simply that the strength of cast iron is not boiling water: there are better tools.

Boiling water is not necessarily going to ruin you cast iron, but it’s definitely not going to improve it. In the same vein of thinking, adding liquid to you recipe is fine, though these are not the dishes that build up the seasoning nor make it better. Water in your pan or pot does not follow the basic principle that heat and oils are improving your seasoning. And some have argued that boiling water alone (or with salt or pasta) can actually loosen the seasoning on your pan and cause it to flake off.

In a pinch (say out camping with a single pot) sure… heat up that soup, steam your veggies over the fire, and just use your iron. That’s what you’ve built up that legacy seasoning for, after all. But know that you’re withdrawing from the seasoning bank you’ve been saving into.

So again, there are better tools. Keep and use a steel pot, and save your cast iron for what it does best. Not boiling water.

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Can I use a self-cleaning oven to strip a cast iron pan?

The short answer is yes.

The more complex answer is … maybe.

A self-cleaning oven is the closest most of us have to a blast furnace inside of our homes. And as many people will tell you while there are multiple ways to strip old seasoning from cast iron, the high heat of an oven’s clean cycle might be the simplest.

My oven claims that on self-clean mode the temperature gets to nearly 900 degrees Farenheit (or about 480 degrees Celsius.) That’s hot. Hot enough to incinerate the seasoning off of any pan.

So what is cast iron seasoning anyhow that we can burn it off our pans, pans that we use over heat all the time?

The back side of a small cast iron pan sitting atop a cutting board.

Cast iron seasoning is a layer of polymerized oil.

Oil is a word we use to describe a vast variety of chemicals with complex molecular structures and specific physical properties. Cooking oils generally come from crop plants and we can eat them.

Polymerizing is a fancy way of saying that many smaller molecules can be chained together to form one massive molecule. Plastic, rubber, nylon are examples of polymers you might be familiar with already. Cast iron seasoning is also a type of polymer.

Cooking oil at the right temperature can be turned into a polymer onto many types of surfaces. We take advantage of this process to season cast iron cooking pans, covering them with lots of very large oil polymers that at the correct window of temperatures create a non-stick cooking surface. Simplistically, we are creating a kind of coating by linking uncountable small oil molecules together using heat.

This coating improves and strengthens with just enough heat, but as with many types of natural compounds if we use even more heat we can destroy it too. By design, because we like to have clean things, it incinerates at the same temperature of other charred food bits, grease, and cooking stains… or the temperature a self-cleaning oven.

So, yes, you can exploit the almost-blast furnace temperatures available in your kitchen to burn the polymerized oil layer from your cast iron pan and “clean” it bare in your self-cleaning oven. Almost 900 degrees Fahrenheit will reduce those polymerized oils to a fine ashy powder that you can wipe off with a damp cloth.

The maybe part of this answer is that high heat is unpredictable. Even some of the best cast iron is not made as uniformly as it may appear as you heft that heavy pan onto the fire. Pans are meant to be heated and then disperse that heat in a specific way (into food, into the air, etc.) So when you heat a pan in very hot in contained space, in a way it was not designed to be heated, there is a chance it could crack or warp.

I’ve personally stripped multiple pans by this method and never had a problem, but all of those pans were replaceable and inexpensive. If I was restoring something more valuable or an antique, I might not take the shortcut of a self-cleaning oven.

So again, can you use a self-cleaning oven to strip a cast iron pan… maybe. This method is fast and convenient (especially if you’re already cleaning your oven) and you can start fresh with a bare metal pan. This might be worth the maybe.