What is the point of the "oven" step in seasoning pans?

Question

Many or most sets of instructions on how to season cast iron and carbon steel follow these steps:

1. Clean
2. Get really hot on the stovetop
3. Apply a very thin layer of oil
4. Heat for a short time, then take off the stove
5. Put it upside down in a medium oven for an hour
6. Cool
7. Repeat if necessary

Examples of these instructions: cast iron dutch oven; carbon steel pan.

Thing is, I've seasoned more than a dozen pots and pans, both cast iron and carbon steel, including both seasoning from scratch and restoring damaged seasoning. I've never done the oven step, and haven't noticed any deficit thereby.

Am I missing something? Is the oven step necessary? What does it actually do?

Answer 1

The primary benefit of seasoning in the oven, rather than on the stovetop, is that the sides of the pan are also heated. (Cast iron has low heat conduction, so the sides of the pan may take a long time to come up to temperature, if they ever do.) The degree of this advantage depends on your pan and cooking surface: large pans on small halogen elements won’t work as well as an oven, while small pans on large gas burners might do as well as in the oven.

Answer 2

For me, the oven simply works better than the stove. It is the stove that you can skip.

First, the heat. It is the same principle as with many foods. A pan heats quicker, but with more variability. An oven is slow and steady, and reaches equilibrium more easily - and it is much easier to control the equilibrium temperature. On a stove, especially empty pan, a low heat will not be enough to polymerize the oil, so it is tempting to turn up to high heat - but then you have to manage to not overheat it and either burn away the seasoning while it is happening, or produce a different reaction - I don't know which one it is, but I suspect it may be the non-rust iron oxide, from the looks of it.

Second, the layer thickness. If your oil layer is too thick, you don't get seasoning, you get a puddle of hot oil. If you continue heating that for too long, you get a thick crust of soft polymer that is prone to peeling off, instead of a thin layer that is well-stuck. A thin layer is optimal, but difficult to produce - the usual method of letting the oil spread by flowing (aided by tilting the pan) makes it too thick. Smearing it with a towel (paper or cloth) gives you a good thickness, but you get a bit of lint onto the pan, especially if the surface is rough, like cast iron. What works well is to cover the pan well with the tilting method, and then have the excess drip slowly when heated to low enough viscosity - which happens automatically during the upside-down seasoning in the oven.

Third, there is the "how to season the sides" problem that Sneftel covered.

Fourth, if you don't have a hob that is the exact same size as the pan, the high temperatures on the empty pan can easily cause warping, especially in thinner forged iron pans.

Fifth, seasoning on a stove is a very active process. You have to manage the heat, keep an eye out for an overheating (warping or fire risk), look for hot spots and possibly rotate the pan, and look out for oil pooling into an undesirable thick layer. In the oven, you set it and forget it.

In summary, the oven is simply the much friendlier way to do it.

Answer 3

Everything already said looks great and valid in most situations.

To add just a few minor things:

1. Cast iron is particularly poor at heat conduction. So heat from a non-global source will definitely not heat the pan uniformly except by a "perfect storm" of coincidences that would be unlikely to repeat. Still may not be an issue as the range of temperatures you get in the stovetop pan may just be perfectly fine for polymerizing the oil you use. But if you find that not working for you regularly, the oven is a better bet as the source of heat is all around the pan. Certainly a single heating element in use gives directionality to that, and two still do as "top and bottom" is still not the same as "top/bottom, left/right, and front/back." The main desirable element is that instead of the pan's material having to spread the heat uniformly, which it won't, the air in the oven is meant to, which it will. Additionally, a heat source with high temp 6"-8" away diffusing into the air that surrounds the whole pan will not create temperature disparities in the seasoning surfaces like a hot burner directly touching some portion of the pan will. So more regularity in the work being done giving you, the non-professional seasoner, a much better shot at great seasoning. The placing of a sheet pan below the pan to catch drippings will also diffuse the heat from the source.

2. The oven seems in practice to be a much slower method which almost certainly allows for a more "even" or "consistent" seasoning layer. Since thinner layers/spots are not as helpful and would wear more quickly, hence requiring re-seasoning sooner, less variance on the thin side seems a good thing. Thicker layers seem like they'd be more prone to be, or have at least on their "tops" the soft polymerization mentioned (that sticky, gooey, hard to clean mess one gets with baking dishes and pans, especially sheet pans). A more consistent layer without that happening also seems desirable. So as the oven seems likelier to not have either to the extent stovetop seasoning might, it seems the option for a longer-lasting seasoning.

3. That said, I have never seasoned a pan after the first seasoning. I don't have to. If I could say why for sure with science to back it up, I'd've led with that, but I don't have to. The last pan I bought I didn't even do an initial seasoning. I do cook with oil and it seems my stove burners are just the right heat for the contents of the pans and oil used (butter or veggie oils of various types) to re-season in use. I don't do anything out of stovetop cooking, so pan-to-oven, no pan-to-grill or vice versa, nothing "foodie" with them. No using it as a watery casserole cooker or using strange oils. No making cornbread or similar things. Just frying things up. So my usage, which has limited range, may be the key. I also use metal spatula-type tools, rigid ones, not flex ones, and their scraping may keep peaks ("tops" when mentioned above) from being a thing by scraping them down constantly. And so the end result might be that the basic layer is not affected much and thin places passed over, allowing them to be thickened by the "cooking seasoning" happening when you fry with oil. Completely experiential, not applicable to someone with a more varied, and perhaps waterier, range of cooking materials perhaps, but maybe. I clean with soap and water, with a cloth, usually do not need to scour (the metal tools already have, broadly, except for the sides). I realize this does not seem to directly address "why oven step" but it does. Due to the contents in the pan while under heat (oil spread everywhere, meat or veggies in place, working them now and then probably mostly just keeps the oil present spread evenly, nothing trying to take the oil's place on the surface, the metal tools scraping away peaks before they form enough to turn nasty and useless... all these things seem very much like they accomplish the even application of heat an oven step does.

4. I believe, though cannot say scientifically, that excess oil in places, created by foods that reach a point that they start to constantly exude oil and so have a pool that spreads away, but is constantly replenished so is effectively always present, but not heating up completely as the hotter bits run away and are replaced by cooler oils exiting the product, causes local hot spots under them which may cause that spot's polymerized material to be destroyed, or harmed toward ruin, and thereby fail, leading to rust being able to form under it and/or it flaking off. So pan-to-oven with a steak might be great for the steak, but not so much for the pan but not really be generally recognized as a problem. Making a cornbread or bread in the pan might do much the same, except via insulating the surface allowing temperature to rise to high for the seasoning across the covered surface. Not a problem when making a pancake (seems like that'd be more of an issue of moisture seeping into microfractures in the polymerized surface), but bake something on stove or in the oven for 10-20+ minutes and the insulating effect might be important. This harkens back to the steeper temperature profile stovetop seasoning must surely have compared to the shallower profile an oven step provides. Just to emphasize the more even, "gentler" if you will, heating in an oven.