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I've been recommended to reoil my cast-iron pan by letting it absorb some oil on the remaining heat of the stove before drying it, each time after using it.

Is it important to do so, and what difference does it make? There should still be a lot of fat left from simply rinsing and drying the pan.

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My $0.02: you don't have to do it every time. Depends on the condition of the cast iron. –  FuzzyChef Jan 18 '12 at 5:35

4 Answers 4

up vote 8 down vote accepted

AFAIK you need to heat the pan to let the oil oxidize and polymerize¹ so that it will form a chemically protective and non-sticking coating.

If you wash your cookware with soap you will have to do it every time. For that reason some people don't wash cast iron at all and wipe it with a clean cloth or paper towel after using. (Burned oil is apparently not very tasty to bacteria and fungi so your pan stays relatively clean and bug-free.)

From my personal experience, meat sticks to untreated cast iron like glue, but on a well-maintained thick iron pan it glides like on Teflon.

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¹ I don't know if it makes any chemical sense because all references to polymerized fats I could google up were in relation to reoiling (seasoning).

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sherylcanter.com/wordpress/2010/01/… ← Here is a method of getting a nice smooth surface by coating the cookware in an oven with flaxseed oil 6 times. I didn't try it myself but to me it looks legit. –  Mischa Arefiev Jan 17 '12 at 12:24
    
@ Mischa: I was going to link that! ^_^ Her "previous post" mentioned in the first paragraph is also good for info on stripping a pan before re-seasoning it: sherylcanter.com/wordpress/2010/01/… –  Scivitri Jan 17 '12 at 17:14

Typically I (occasionally rinse and then) heat the pan and grease with shortening when the seasoning looks like it could use a touch up. When dirty, I heat with a bit of oil and clean out with salt; this reduces the viscosity of the oil making it likelier to fill in the porous surface of the skillet. Since it appears you are asking specifically why the fat/oil needs to be heated, I will address that. However, there is already wealth of information on cast-iron seasoning in these two earlier posts.

The purpose of the heat is three-fold;

  • if you previously rinsed it will help evaporate the water
  • by heating the surface you make the grease (or oil if you like) apply more evenly and thoroughly due to the lowered viscosity allowing the oil to penetrate deeper into smaller pores/pits of the iron
  • if you haven't used the pan in a while the seasoning (because it is composed of fats and oil) may go rancid and the heating can prevent that.
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Thanks. I meant to ask about the whole reoiling process, and why it isn't enough just to rinse the pan in water. –  user4697 Jan 17 '12 at 17:34

Iron rusts. A protective coating of oil helps to prevent the rusting. I've found that my cast iron pans rust less and need less protection as they acquire the sort of patina that Mischa describes.

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I realise the importance of a good seasoning; I'm just wondering if reoiling after usage is required to maintain the seasoning. –  user4697 Jan 20 '12 at 17:58

Yes you should season the pan after each use. I've used the Flaxseed oil principle. It does work, but it makes the pans smell strange and the food tastes a bit weird. This is because it is food grade linseed oil. This kind of oil is used for oil paintings.

The best thing is to use either vegetable shortening or lard. You can heat the pan on low heat. Use a cotton cloth to spread the vegetable shortening inside the pan, then crank up the heat to 7 or 8 until there's a bit of smoke. This is the carbon layer being burned onto the pan. Wipe the pan down again and place in the oven to cool.

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why should a pan be seasoned after each use? Sounds like lots of unnecessary work. I (and other people I've talked to) don't do it, and our pans seem to be fine. –  rumtscho Jan 23 '12 at 8:37

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