Cast iron: seasoning, care, and restoration

[Chris Hennes]

Thanks, that's very helpful. I presume that there is no reason to stick with veg. oil, is there? Right now I have it in the oven with some duck fat because I had just a little bit leftover.

[paulraphael]

Thanks, that's very helpful. I presume that there is no reason to stick with veg. oil, is there? Right now I have it in the oven with some duck fat because I had just  a little bit leftover.

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The ideal oils to use are ones highest in polyunsaturated fats ... canola, sunflower, safflower, etc. etc...

These oils will season a pan much, much more quickly and efficiently than anything else. This thing we call seasoning is nothing more than polymerized oil, which is oil that has oxidized and turned to plastic from heat. The fewer hydrogen bonds (meaning, the less saturated the fat) the more quickly and effectively the oil will polymerize.

It's conventional to use veg oil or bacon fat. But it's also conventional wisdom that it takes years to get a good seasong going. If you use the right oil, you can do a great job in two hours. A killer job in a couple of two hour sessions.

The conventional wisdom about how carefully you have to handle the seasoned pans is greatly exaggerated. Those polymerized oils are tough. And they're not soluble in much. You can use detergent and a scrub sponge to your heart's content. That stuff isn't going anywhere. I'd draw the line at using steel wool, or soaking in any kind of concentrated cleaning solutions. But you shouldn't feel the need to ever do this ... these pans tend to clean up easily.

[Chris Hennes]

Interesting, I didn't know that I should be looking for polyunsaturated fats. According to this site I should then be looking for (ranked from best to ok):

1. Safflower oil (74%)
   
2. Grapeseed oil (71%)
   
3. Walnut oil (70%)
   
4. Sunflower oil (63%)
   
5. Corn oil (51%)
   
6. Vegetable oil (48%)
   

[Chris Hennes]

Looking back over this topic and the other topics that reference cast iron cookware there seems to be some inconsistency as to advice given re: the actual best way to season a pan in terms of the nitty-gritty details of it. Right now, I am:

• Using grapeseed oil (very high in polyunsaturated fats)
  
• Putting a thin coat on the piece
  
• Heating the piece in a 250°F oven for 3-4 hours
  
• Removing from the oven and letting cool
  
• Repeat N times
  

Is there anything I should change? In particular, what is the optimal time/temp in the oven? How do you know when one round in the oven is done? Is it necessary to let the piece cool before repeating the steps? I know there are zillions of ways to achieve "good enough" over "time enough" but in terms of the best seasoning in the least amount of time, what is the best practice (bonus points for citing your sources ?

[skipper10]

Thanks, that's very helpful. I presume that there is no reason to stick with veg. oil, is there? Right now I have it in the oven with some duck fat because I had just  a little bit leftover.

←

The ideal oils to use are ones highest in polyunsaturated fats ... canola, sunflower, safflower, etc. etc...

These oils will season a pan much, much more quickly and efficiently than anything else. This thing we call seasoning is nothing more than polymerized oil, which is oil that has oxidized and turned to plastic from heat. The fewer hydrogen bonds (meaning, the less saturated the fat) the more quickly and effectively the oil will polymerize.

It's conventional to use veg oil or bacon fat. But it's also conventional wisdom that it takes years to get a good seasong going. If you use the right oil, you can do a great job in two hours. A killer job in a couple of two hour sessions.

The conventional wisdom about how carefully you have to handle the seasoned pans is greatly exaggerated. Those polymerized oils are tough. And they're not soluble in much. You can use detergent and a scrub sponge to your heart's content. That stuff isn't going anywhere. I'd draw the line at using steel wool, or soaking in any kind of concentrated cleaning solutions. But you shouldn't feel the need to ever do this ... these pans tend to clean up easily.

←

What about the "conventional wisdom" to rub seasoned pans with salt?

[paulraphael]

One of the benefits to using something like grapeseed is that you can go a lot hotter.

That is, assuming it's a fairly refined grapeseed oil ... one intended for high heat sautéeing and not for tasty salad dressings. The former tend to be much lighter colored, and not at all cloudy. Some companies are nice enough to print the smoke point on the label.

If it's a light, refined oil, you should be able to put it in at 450 degrees or so. It's not a big deal if it smokes a little.

I find it helpful to use a really light coat of oil. If it's at all heavy, the oil will thin out from the heat and rund down the sides of the pan making drip marks and puddles.

After 45 minutes or so, you can pull the pan out, and with the pan still hot, brush on another very light coat of oil with a paper towel. Obviously taking care not to burn yourself. If you repeat this three times or so, you should end up with a nice, shiny, plasticy glaze.

As you go along, use your intuition to adjust the oven temp, cooking time, etc... I don't know any firm rules for how to determine this, other than a temperature around the oil's smoke point seems to work well.

Edited April 4, 2009 by paulraphael (log)

[Chris Hennes]

OK, oven is turned up now. No smoke point on the can, but I bought it for the purpose of very high-heat sauteeing, so I think it will be OK. I'm astonished by the amount of misinformation about this subject on the web: in particular, a lot of sites actually advise against using polyunsaturated oil, while others claim the oil doesn't matter at all, it's all about the carbon molecules. For the record, here's what McGee has to say about seasoning cast iron:

The oil penetrates into the pores and fissure of the metal, sealing it from the attack of air and water. And the combination of heat, metal, and air oxidizes the fatty acid chains and encourages them to bond to each other ("polymerize") to form a dense, hard, dry layer[...]. Highly unsaturated oils—soy oil, corn oil—are especially prone to oxidation and polymerizing.

Note that in this case we want oxidation and polymerization. And it certainly sounds to me like there is more going on than just bonding the carbon molecules to the iron.

[Hest88]

The conventional wisdom about how carefully you have to handle the seasoned pans is greatly exaggerated. Those polymerized oils are tough. And they're not soluble in much. You can use detergent and a scrub sponge to your heart's content. That stuff isn't going anywhere. I'd draw the line at using steel wool, or soaking in any kind of concentrated cleaning solutions. But you shouldn't feel the need to ever do this ... these pans tend to clean up easily.

ITA, with some caveats. I will *lightly brush* both my cast iron pans and wok with a copper scrubbie and that takes off any clinging food. I will also scrub harder for burnt on food, and it will take off the carbonized food particles rather well without really damaging the coating. But yes, your general green scratchie sponge isn't going to take off a good seasoning, and neither is some detergent--which I will also use if the food is particularly icky. It just stands to reason--how easy is it using detergent to clean the old grease in an oven? It's virtually impossible.

However, I had a heartbreaking incident a few weeks ago which does serve as a lesson. I usually have no qualms about throwing tomatoes or any other acidic food into my old #8 Griswold cast iron pan. It's one I picked up at a flea market many years ago and was midnight black and shiny, obviously through years of use by someone's grandma. Well, I picked up some marinated kalbi at our local Korean market, threw it in the hot pan, and to my dismay, after a few minutes my lovely seasoning started flaking off in large sheets. I don't know what it was about the short rib seasoning, but my pan really didn't like *that* acidity.

Yes, I'm re-seasoning it. And sending my abject apologies to the anonymous grandma who cared for it so lovingly for so long.

[andiesenji]

I think you can use any kind of oil or fat as long as you add it in light coats.

I have a lot of very old cast iron and most of it has been seasoned for as long as I have been alive (70 years) and long before the new type oils, they were all seasoned with lard.

I don't use those pans when I cook for people who have religious dietary restrictions.

My ancient Griswold spider (griddle) gets oiled with a piece of bacon rind (one of the advantages of buying bacon by the slab) and it has a surface that looks like enamel.

[HowardLi]

I had always thought you could season at 250-300F, but believe me, it will take months to get the seasoning going if you never exceed that temperature. If you want to season on any sort of reasonable timespan, you will need to heat the iron until it SMOKES. A LOT. Best to do it upside down on an outdoor grill.

I generally use lard, but I wouldn't hesitate to use any corn oil lying around.

[Dave the Cook]

I've been experimenting lately with using roux -- specifically Prudhomme-style, high-temperature roux, combining high carbon content with fat breakdown -- to get a quick, hard seasoning, and I've had excellent results.

• For a ten-inch pan, heat a cup of highly unsaturated oil (I use grapeseed) until it smokes.
  
• Add a cup of a/p flour and stir constantly until the roux turns dark brown.
  
• Remove from the heat and allow to cool in the pan.
  
• Clean out the pan. The roux, if you haven't burned it, is great for gumbo.
  
• Repeat two more times, and heat your oven to 400 F.
  
• After the third roux and cleaning, use a paper towel to give the pan a thin coating of the same oil you've been using.
  
• Put the pan in the oven for 30 minutes.
  
• Remove the pan and wipe out any oil puddles.
  
• When the pan cools, apply one more coat of oil, leaving no excess.
  
• Your pan is seasoned.
  

I'm not prepared to promote this as a universally appropriate method, but it's worked extremely well so far. I'd love for someone else to try it and post results.

[snowangel]

Let's get back to Chris's taking the power sander to the Lodge pre-seasoned. I also have one, and don't really like it because it seems so rough (pebbely?). Lord only knows why I let my sister have my grandmother's set of Griswolds while I took the cookie cutters, but I did (I also took the china and the card table clothes with matching set of four napkins). But, those Griwolds, smooth as a baby's bottom. Were they rough and pebbely to begin with? Should I take my RA (random orbital sander) to the thing and try any of these seasoning techniques, or is just using the thing that makes them baby-bottom smooth?

[andiesenji]

I bought an 18 inch skillet several years ago and took it to a metal shop to have the inner surface ground and polished - they used a carbide disc which threw up a lot of sparks but it turned out as slick as steel. They also made it perfectly level, no dips and bumps so no puddling of fat anywhere on the surface.

I used it on my portable double gas burner when I would do pancake breakfasts for fund raisers.

It would hold 5 pounds of sausages.

[dougal]

... I'm astonished by the amount of misinformation about this subject on the web: in particular, a lot of sites actually advise against using polyunsaturated oil, while others claim the oil doesn't matter at all, it's all about the carbon molecules. For the record, here's what McGee has to say about seasoning cast iron:

The oil penetrates into the pores and fissure of the metal, sealing it from the attack of air and water. And the combination of heat, metal, and air oxidizes the fatty acid chains and encourages them to bond to each other ("polymerize") to form a dense, hard, dry layer[...]. Highly unsaturated oils—soy oil, corn oil—are especially prone to oxidation and polymerizing.

Note that in this case we want oxidation and polymerization. And it certainly sounds to me like there is more going on than just bonding the carbon molecules to the iron.

←

Unless you are getting into exotic materials (fullerenes?), forget about the notion of "carbon molecules". We may get some carbon, but I think to call it molecular would be misleading.

Oil molecules are in essence long strings of carbon atoms, 'joined' one to the next, (with, in this context, pretty inert hydrogen atoms stuck on the side).

If any of the Carbon-Carbon bonds are 'double' bonds then you have an 'unsaturated' fat. If many are double bonds in the same molecule, its "poly-unsaturated".

If you can induce a double bond to partially break - and become a mere single bond - you thereby get a reactive site on the molecule, eager to find something to join up with.

If two such sites, on different chains, get near one another and join up with each other, (which might be assisted by linking via an atom of oxygen, we've got 'polymerisation' happening.

The double bonds aren't essential, but they should facilitate the polymerisation. (Sure you can polymerise lard, but not I think as easily.)

Get enough oil molecules joining together and the chains get longer, stiffer and more inter-tangled. The molecules lose their ability to move easily relative to one another - and we get something more like a solid than a liquid. Ideally, we want to get past this wax to a 'proper solid'.

With that in mind, we can see what else is happening.

We want our waxy solid polymer to stick to the iron surface. It won't chemically react with the iron, so it has to be mechanically keyed to the surface.

For it to stick (which is what we want), the iron surface must be, just slightly, rough. The more mirror polished it is, the less easily the polymer will stick!

However, that's not really a problem - as long as you prevent the bright shiny surface from rusting! It was said that "seasoning is use" - and so it is; one could just let the patina build up naturally, in its own time. Just wipe it out gently rather than scouring it. And dry it very carefully to prevent rust.

When the fat (or food) burns or smokes, the molecular chains are being wrecked. Those 'inert' hydrogen atoms are joining up with oxygen (the resultant water escapes) and bits of carbon get left behind. Get it hot enough for the carbon to react with oxygen and we describe the result as 'catching fire'.

We don't want a fire, but we do want some carbon. The carbon will be in a messy structure based on that of graphite (sorry, you aren't anywhere near the conditions for carbon's other structure - diamond). But that sooty, graphitic carbon makes a great "non-stick" lubricant.

But it doesn't stick, by itself, to iron.

Which is where the polymer comes in!

We want to trap/embed bits of carbon in the polymer which is itself mechanically keyed to the iron surface. And, I reckon the black surface produced by seasonong is going to be itself somewhat micro-porous, so it will hold a little oil for lubrication and also more polymerisation.

So, we want two things to occur. 'Smoke' to get the carbon, AND our waxy plastic polymer to hold the carbon, and to hold all this stuff to the iron.

So, to obtain the carbon that is going to be embedded, it's important to get to 'smoke' temperature - just as HowardLi describes. And it might help to have additional sources of carbon (like Dave the Cook's flour), though I suspect that would make it hard to get an even layer. And for the 'smoking' oil or fat, it shouldn't matter whether its poly-unsaturated or fully saturated.

But first, we need to lay down some sticky (waxy) polymer.

Now, if anyone says that what we really want to do is to lay down our polymer, keyed to the iron, and then 'carbonise' that polymer - I'd say fine, there's probably quite a lot of that going on as well.

However, the important thing is to recognise that there are two processes, polymerisation and carbonisation. And we need both.

The quickest route to 'blackening' a distressingly shiny pan (if the shine worries you), would probably be to get a thin but nicely even 'gummy' layer (from mid temperature heating, 130C?, of a rewiped but thin layer, 3 wipes over 90 minutes?), before 'smoking' the thing at a very high temperature, until it stops smoking! To minimise the thermal shock on the way to seriously high temperatures, you could heat the pan in the oven before putting it over charcoal .

Similarly, this smoking phase might indeed be performed with a blowlamp, but it would be much more considerate to the pan (thermal shock minimisation) to get the pan properly hot before showing it the flame.

But, its the slow building up of the 'burnt grease', in multiple thin even layers, and immediately wiping out the pan gently, that would give you the even-ness of build-up, rather than merely a filthy crusty old pan.

This should be where the salt comes in.

Salt crystals are being used simply as an abrasive. No magic, no chemistry, just mechanical abrasion.

If you 'sand' down the lumpy bits of 'crust' with a salted cloth, you'll get a smoother, less lumpy surface ... BUT, its not something you'd be doing unless your wipedown had failed to give you a smooth surface.

Its noteworthy that in Andiesenji's splendid photos, the only 'rough' surface in the cornbread pan is above the level to which the pan is routinely filled!

"Seasoning is use" ...

[Chris Hennes]

OK, chemistry was never my strongest course (obvious from my mislabeling carbon as a molecule!): I am trying to understand precisely what is meant by "mechanical" adhesion to the surface, at a molecular level. So there are no bonds between the iron atoms and the polymer molecules? Is the idea that some of the polymer chains get tangled up or "wedged in" microscopic crevices in the pan's surface? How strong is this adhesion?

[Chris Hennes]

Let's get back to Chris's taking the power sander to the Lodge pre-seasoned.  I also have one, and don't really like it because it seems so rough (pebbely?).  Lord only knows why I let my sister have my grandmother's set of Griswolds while I took the cookie cutters, but I did (I also took the china and the card table clothes with matching set of four napkins).  But, those Griwolds, smooth as a baby's bottom.  Were they rough and pebbely to begin with?  Should I take my RA (random orbital sander) to the thing and try any of these seasoning techniques, or is just using the thing that makes them baby-bottom smooth?

←

Actually, after applying the knowledge gleaned above about seasoning, I took both my un-sanded pan and my sanded pan and did the the high-heat grapeseed oil seasoning steps three times. The surface smoothness is now a) awesome and b) indistinguishable between the two. The polymer layer that formed is thick enough that it smoothed right over the roughness of the unsanded lodge pan.

To be honest, until I got serious about seasoning my cast iron I had always figured that the "practically nonstick" claims were a bit bogus, mostly wishful thinking on the part of the nostalgic cast iron owners. Turns out I was completely wrong: these pans are really actually honestly nonstick. Like, probably more non-stick than my well-used mostly-still-teflon-coated pans. Amazing. Better living through chemistry...

[slkinsey]

Eh...? I think you'll find that if you drop an egg into your cast iron pan with no fat and do the same thing with your PTFE-coated pan, you'll see that the PTFE-coated pan is significantly more nonstick than your cast iron pan.

Cast iron can be realtively nonstick given certain parameters. One of those parameters is the presence of plenty of fat. You want to cook up some sausages? Nonstick. Coat the inside with oil, heat it up and cook some cornbread? Nonstick. Crispy-skin fish without breaking the skin? Not likely. Scrambled eggs in minimal fat? No way.

[Chris Hennes]

OK, I admit, I hadn't actually tested cooking without fat—I always add fat to the pan, nonstick or no. And sure enough, slkinsey is right (again), an egg cooked without added fat in my freshly-seasoned cast iron skillet (dry of any surface fat) stuck, whereas, of course, the egg cooked on the teflon-coated pan only stuck where the teflon had worn away. Moral of the story: fat is good . And you need it to cook in cast iron.

[dougal]

... I am trying to understand precisely what is meant by "mechanical" adhesion to the surface, at a molecular level. So there are no bonds between the iron atoms and the polymer molecules? Is the idea that some of the polymer chains get tangled up or "wedged in" microscopic crevices in the pan's surface? How strong is this adhesion?

←

I doubt there's any significant chemical bonding/reaction between the iron and the 'seasoning'.

I think its going to be almost entirely mechanical. So, yes, hooked in, 'keyed' into defects in the surface, though there may be other effects - even atmospheric pressure would likely also be helping to hold the skin in place.

So I was thinking that a 'rough' (sandblasted and cleaned?) surface would be a better substrate for seasoning than a mirror polished one.

But the skin of seasoning is relatively weak, and weakly attached. Which is why you don't go scrubbing at the thing to clean it.

I understand the prime reason for 'seasoning' as being to protect the pan (and thereby you) from rust.

The seasoned surface is also supposed to be somewhat microporous - both giving cooked food something to catch onto, and also somewhere to hold a wipe of oil.

So that it does cook (and releases) better with less oil than an unseasoned surface.

Edited April 7, 2009 by dougal (log)

[andiesenji]

Just as a side note. Last Saturday on America's Test Kitchen they reported on their testing of various 12-inch skillets, including non-stick, regular cast iron, enameled cast iron non-stick (Le Creuset) and carbon steel skillets.

They also had one of the nickel-plated skillets which they did not think was worth the price.

The Le Creuset was great but too expensive for most cooks.

They rated the inexpensive Lodge Logic pre-seasoned as the best buy at $27.00.

[Dave the Cook]

. . . .

But the skin of seasoning is relatively weak, and weakly attached. Which is why you don't go scrubbing at the thing to clean it.

. . . .

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Perhaps this is true, but 1) the seasoning on my pans is pretty tough -- anything short of a stainless steel sponge is safe to use, I regularly let them soak, and I'm not afraid to use soap or detergents; 2) you don't go scrubbing at the thing because if your pan is well-seasoned, you don't have to; 3) losing the seasoning is no big deal (I think the most common cause is not scrubbing but overheating) -- just reseason it.

[Octaveman]

Eh...?  I think you'll find that if you drop an egg into your cast iron pan with no fat and do the same thing with your PTFE-coated pan, you'll see that the PTFE-coated pan is significantly more nonstick than your cast iron pan.

Cast iron can be realtively nonstick given certain parameters.  One of those parameters is the presence of plenty of fat.  You want to cook up some sausages?  Nonstick. Coat the inside with oil, heat it up and cook some cornbread?  Nonstick.  Crispy-skin fish without breaking the skin?  Not likely.  Scrambled eggs in minimal fat?  No way.

←

I really don't have first hand experience with this from the standpoint of a controlled study so I'll just present what I've read.

First, with carbon steel or cast iron, the metal is somewhat porous in that there is expansion and contraction thing going on. Thus any fat that was in the pan as it cooled was trapped in the porous confines of the metal. Then when the pan was reheated it releases trapped fat providing the amount needed to make the pan have non-stick properties. Fact or myth?

Second, I've read that the surface type has a lot to do with how "non-stick" cast iron is. Lodge for instance is poor in this regard in that the surface is bumpy. Cast iron pans of yesteryear like Wagner and Griswold were as smooth as a baby's butt which is likely the reason for what we have all heard about cast iron pans eventually becoming non-stick. Fact or myth?

Third, there is a certain element of non-stickiness to stainless steel pans if you leave the food alone until it releases. Once the food browns food does not stick. Some fat was added, sure, but if you take into account the greased up seasoning that already exists on cast iron pans that would be the same as adding fat to a dry SS pan. Fact or myth?

So, given the above, if I had a baby's butt smooth cooking surface that was properly seasoned and was maintained properly, and I let that egg cook undisturbed on the thin film of fat the pan gave off it would release enough to be flipped. Fact or myth?

[slkinsey]

I believe that the "releasing a thin film of trapped oil" bit is a myth. Read dougal's good explanations above (starting around here).


I should also add that I've got antique Griswold that has been in my family for around 100 years, and it is not what I'd call "nonstick" by the standards of a PTFE-coated pan.

Edited April 7, 2009 by slkinsey (log)

[paulraphael]

Dougal's explanation is excellent. The part of the equation I've always missed is the importance of the carbon you get from smoking the oil. I've gotten my best results when the oil gets hot enough to smoke at least a bit, but didn't know why this would be.

Makes sense, because the unblackened polymerized oil that I've accidentally gotten on other pans is anything but nonstick.

It's also next to impossible to remove. This stuff isn't fragile.

[andiesenji]

Dougal's explanation is excellent. The part of the equation I've always missed is the importance of the carbon you get from smoking the oil. I've gotten my best results when the oil gets hot enough to smoke at least a bit, but didn't know why this would be.

Makes sense, because the unblackened polymerized oil that I've accidentally gotten on other pans is anything but nonstick.

It's also next to impossible to remove. This stuff isn't fragile.

←

I can solve this problem for you with very little expenditure of money or effort. Particularly good for the burnt-on spots on stainless steel and even on chrome-plated appliances.

Take a slightly damped cloth, just damp enough to pick up dry baking soda when you dip the cloth into some which you have placed on a saucer.

Rub the spot or spots, using a clean spot on the cloth and another dip of baking soda when needed.

I have a fairly large collection of "vintage" or nearly antique electric appliances from the '20s and '30s and the only way to clean them without damaging the chrome finish is this method. I have tried commercial cleaning compounds and while some make the job easier, they all have an undesirable effect on the chrome finish.