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It is well established in the scientific literature that those cooking on stainless steel cookware get a portion of their daily iron intake from the iron in the pan that makes it into the food:

  1. Geerligs, Brabin, and Omari, Food prepared in iron cooking pots as an intervention for reducing iron deficiency anaemia in developing countries: a systematic review, J Hum Nutr Diet. Aug 2003, Vol. 16, Num. 4, pp. 275-81.
  2. Kollipara and Brittin, Increased iron content of some Indian foods due to cookware, American Dietetic Association. Journal of the American Dietetic Association, Vol. 96, Num. 5 (May 1996)
  3. Kuligowski and Halperin, Stainless steel cookware as a significant source of nickel, chromium, and iron, Arch. Environ. Contam. Toxicol. (1992) Vol. 23, Num. 211.

For most people that's not a bad additional nutrient, and those who saw family use a stainless steel pan surviving a lifetime know that the lost steel will not wear a pan out, not even after decades of use.

I'm now giving up on finding a tri-ply skillet whose bottom will remain perfectly flat. Since I cook on ceramic, a cast iron skillet is a good option. I'm hoping this would lead to steaks cooked perfectly evenly.

Suppose I'll use the cast iron skillet for literally just steaks, I'm concerned about the burned fat from the skillet's seasoning that will leach out to the steaks—in analogy with what happens when cooking in stainless steel cookware.

When you cook with cast iron, how do you know that some of the fat from the food you're cooking makes it to the skillet, but never the other way around. How do you know that the burnt pan "seasoning" does not make it into your food? Without some kind of confirmation that the burnt pan seasoning is safe, it would be nice to confirm that this does not occur in even trace amounts?

I'm guessing that deglazing the pan after cooking steaks would only increase the chance of this leaching in the undesirable direction. Hints for safe deglazing are also welcome.

update: A possible litmus test to determine potential leaching is to wipe with a paper towel.

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Calaf
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    I'd just note that if your primary reason for switching to cast iron is because of fear of warping, just know that cast iron *can* warp too, though it's rare. But if you do a lot of searing at high temperatures, etc. with cast iron, some pans will warp. I've seen it personally with a thick vintage cast iron skillet I own (and which is now practically useless on flat-top stoves). On the other hand, over the years I've owned quite a few cheap tri-ply pans, and I've only had one warp significantly on me. YMMV. – Athanasius Aug 21 '16 at 20:32
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    Fat turning into slimy bloodsuckers and invading the food, hmmm. What horror movie are you posting from? I don't want to watch it by accident. *Hint - look up leach and leech, they are not the same.* I also seriously doubt the validity of your "I read it somewhere" presupposition that stainless steel is a significant source of dietary iron. – Ecnerwal Aug 21 '16 at 22:22
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    I don't get the paper towel thing - as answers there say, you can easily get a thin layer of burned food on the pan, and that will turn a paper towel black, without any seasoning coming off. Are you thinking of seasoning as being burned food? – Cascabel Aug 22 '16 at 18:18
  • @Jefromi seasoning *is* burned food. A rather specific kind, if you manage it well, but still. There are people who don't season a new pan at all and simply cook with fat daily, waiting to build up by itself. – rumtscho Aug 22 '16 at 18:33
  • @rumtscho Should've been clearer: burned food besides polymerized oil. If the oil's fully polymerized, it won't rub off, so if something black is rubbing off on a paper towel, it's something else burned on there besides the seasoning, or something you've not bothered to clean off. (Might be deliberate, as you say, but it's still not the seasoning rubbing off.) – Cascabel Aug 22 '16 at 19:11
  • I'm not sure I want to get involved in this question, since I think any answer I attempt will skirt too close to "health effects" issues and thus be off-topic. Suffice it to say that--in my opinion--you're probably looking in the wrong place if you're worried about cast iron seasoning flakes. The concentration of hazardous compounds is going to be much greater in seasoning fumes/smoke than in the large polymerized chains in finished seasoning. For that matter, the amount of nasty compounds in browned/charred pan-fried steak itself is likely to be higher than from the seasoning oil. – Athanasius Aug 23 '16 at 04:32
  • @Athanasius The leaching concern I assume is originating from a concern about the health implications? (at least it is for me) If so, then in that case a 'health effects' reply would not be off topic? – redfox05 Aug 17 '17 at 01:12

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Have you ever had the experience, when cooking in stainless steel, of the oils browning onto the edges of the pan? You know, the brown gunk that is really tough to clean off...it usually takes a scrub pad, some elbow grease and some abrasive cleaner. That is polymerized oil. The idea behind seasoning a cast iron pan is to create a surface of polymerized oil. It's not burnt oils. It is really a pretty tough surface when done correctly. On top of that you would typically add some fat (for example when searing), though that might not be necessary depending on your cooking method. The idea that the seasoning would somehow contaminate your food is hard to imagine. A well seasoned cast iron pan will generally hold up to deglazing...and even a light washing with soap and water. This is how I think about it as an informed cook. I would welcome a more informed response from any one with expertise in the actual science.

moscafj
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    The only time that I can think of when the seasoning would get into your food is when you scrape the bottom w/ a metal spatula or similar. But you actually *want* to use metal utensils to knock down any high points that might form to get a smooth surface. So it's possible that I'm eating it ... but it's just going to pass through you, like sawdust in diet 'high fiber' muffins. (okay, technically, cellulose, but it comes from wood) – Joe Aug 21 '16 at 21:09
  • @Joe The assumption you state (passing through you) is quite a steep one. It would be nice if that's the case. If the seasoning on the pan is a result of the Maillard Reaction (https://en.wikipedia.org/wiki/Maillard_reaction), then perhaps it's not too bad, but given that the recipe for (re-)seasoning involves burning oil at somewhere between 350F and 400F, the compound may be a bit more sinister. – Calaf Aug 21 '16 at 22:15
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    @Calaf : well, cast iron pans have been used for centuries ... if they're killing us, it's very likely that we'd know it by now. And no, it's not maillard -- that's for proteins, like caramelization is for sugars. This is polymerization (cooking oil to become a type of plastic). If you're burning it, you're doing something wrong. – Joe Aug 22 '16 at 01:01
  • @Joe We're on to something. With any new stove, I find it's essential to experiment until I nail down the temperature at which I get the perfect omelette (and steaks, etc..). It turns out this is the Maillard temperature. Now you seem to be suggesting that there is a similar temperature I should be seeking when seasoning a cast iron skillet. It should be higher than the one I'd be using for cooking, but not so high to cause burning of the fat. Does this temperature have a name? I seek Maillard with butter. How do I seek that polymerization temperature? – Calaf Aug 22 '16 at 01:26
  • You seek that polymerization temperature by finding a good seasoning guide and seasoning at the temperature it tells you to use. It will either give you a surface temperature to measure, or an oven thermostat setting to use (oven seasoning is easier), or tell you what to look for when seasoning to recognize that you are doing it right. – rumtscho Aug 22 '16 at 18:49
  • @rumtscho, so that sounds great, and exactly what I (and others) probably need. Can you therefore point us in the direction of such a seasoning guide, as this would help more than just saying we need a good guide, cos thats why we're here reading this question. – redfox05 Mar 05 '17 at 01:04
  • @redfox05 I don't have a specific guide in mind, you have to search around until you find one that works for you. Also, if "how do I season a pan" is what you need, then this question is irrelevant for you anyway. You could start with http://cooking.stackexchange.com/questions/641. – rumtscho Mar 05 '17 at 14:39
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You don't know it. In fact, I think that trace amounts of it end up in the food. With very new seasoning or also badly made seasoning, I have seen some "wear out" on pebbly pans. Not outright flaking, simply the hills of the pebbles looking a different, unseasoned color after dryish cooking on higher temperatures.

The sources you read are a further hint. The one you linked is the only one I've ever seen claiming that stainless steel provides dietary iron, and it is written confusingly, starting to talk about SS but later saying that it is iron pans which contribute to dietary iron. There is some exchange in matter between the pan itself (beneath the seasoning) and your food, and as far as I am aware, also between the seasoning and your food.

Third, the above is about standard, well made seasoning, which still gets somewhat abraded and repaired in microscopic amounts with each cooking. If you manage to burn stuff onto seasoning (carbohydrates in combination with high temperature are the worst there), it won't clean completely with scrubbing, but will continue coming of with use. No visible residue in the food, but months later, the rough charcoal structure will be gradually gone.

I don't have any firm sources from somebody who measured this in a lab. But from everything I have observed while using and misusing seasoned pans, there is some transfer happening in both directions, in trace amounts.

rumtscho
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Yes some of the seasoning as in polymerized fat and oil will dissolve into the food. It is just oil - I find no indication it is toxic. If it was toxic should not be using it for seasoning in the first place. It is a very small quantity.

And I don't agree with the word leach here. Part or (maybe even all) of the surface coating is dissolved. Maybe even a little will ware off. Leach is to exact a component from a solid such as an acid will leech some iron from a cast iron pot.

leach WIKI

paparazzo
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  • @JonTakagi You can create a new room yourself if you like. Actually moving requires either discussing long enough for the site to automatically suggest it, or a mod's help. Since I happen to be here... [moved to chat](http://chat.stackexchange.com/rooms/44375/discussion-on-answer-by-paparazzi-how-do-you-know-that-the-cast-iron-seasoning-d). – Cascabel Aug 23 '16 at 16:53