There are dozens of articles and videos on the Internet that explain how to season cast iron cookware, but instructions vary widely. No one can agree on the best oil to use; some prefer Crisco or even lard. Oven temperatures range from as low as 250°F (~120°C) to levels that can only be reached by using an oven’s self-cleaning feature—a practice we strongly discourage. Some sources claim one seasoning is all it takes, while others advocate several attempts to attain the proper surface.
We tested many approaches with mixed results, often ending up with a blotchy, somewhat tacky surface inside our skillets. To know the best way to treat a pan requires a little understanding of the science behind seasoning.
The process of seasoning a pan is scientifically known as polymerization, wherein a relatively small amount of oil is applied to the surface of cast iron cookware and subjected to high heat, during which the oil molecules transform or polymerize into a thin hard layer not all that different from varnish. In fact, when you season cast iron you are essentially varnishing it.
All of that seemed easy to grasp, but sorting out the finer details, such as which oils and temperatures work best, required a deeper dive. Initially, we were concerned that using oils with lower smoke points would result in the formation of free radicals, which are known to pose health threats, but this turns out to be precisely what polymerization is all about. During the process, free radicals release and cross-link into something altogether different.
Armed with this knowledge, we returned to our test kitchen to figure out the best way to season a cast iron pan.
The Best Oil
Suffice it to say, that all cooking-grade oils eventually polymerize at one temperature or another. Oils with higher smoke points simply require more heat in order to polymerize, and the release of free radicals poses no health risk. The best oils turn out to be those that are unprocessed and have no additives. It’s hard to know what becomes of additives at high temperatures. At best, you don’t want to bake them into your seasoned finish.
We prefer sunflower or soybean oils for two reasons. They are relatively inexpensive and easy to find. And both have a high iodine value, which, oddly enough, has nothing to do with the amount of iodine in them but is a good indicator of how well the oil will polymerize.
Some people truly prefer Crisco over oil, but Crisco is predominately soybean oil mixed with fully hydrogenated palm oil, diglycerides, TBHQ and citric acid. You’re better off with plain soybean oil.
Sheryl Cantor, a writer who has extensively researched the science of seasoning and writes about it on her website, prefers flax seed oil, which worked well for us but is twice the price of sunflower oil.
Heat & Repeat
We definitely found that hotter temperatures—those in the 450-500°F (230-260C°) range—for a duration of one hour yielded better results than a more moderate oven. This is probably because the higher heat insures a more thorough process in that amount of time.
Another advantage of the hotter oven temperature is that it works with a broad range of oils. All of the oils we tested had smoke points below 500°F (260C°). If you intend to use a moderate oven, double-check the smoke point of the oil used. Most refined oils have smoke points in excess of 350°F.
The number of times to repeat the seasoning process depends largely on whether the pan has been pre-seasoned. Today’s cast iron manufacturers have done some of the work for you by seasoning pans during the factory process. Lodge, the iconic brand leader, pre-seasons all of their cast iron products using a proprietary oil and process that they claims is the equivalent of 15-20 seasonings.
That could certainly save you a lot of effort, but we found that even pre-seasoned pans still benefited from one or two in-home treatments. Pans that had not been pre-seasoned or had been stripped of their seasoning completely need 4-5 seasonings before forming a respectable finish.
After each seasoning, we tested the pans by frying an egg in a teaspoon of oil; after five rounds of seasoning, the pans performed well. We also found that the more you seasoned the pan, the better it stood up to a long soak in hot water.
If you don’t have 4-5 hours to spare, you can spread the sessions out over time. An Oven with a timer comes in handy. Set it for an hour of seasoning each morning before going to work, and by the end of the week, you’ll have the patina you’re looking for.
Keep a Good Thing Going
Seasoning cast iron in the oven is simply the first step. A good season will continue to build-up over time, and there are some real do’s and don’ts that can help you in that endeavor.
Don’t use soap to clean seasoned cast iron. For most clean-ups, some hot water and a nylon bristle brush or pot scrubber will be fine. If you’re a little germophobic and reluctant to give up soap, keep in mind that bacteria cannot live at temperatures above 212°F (100°C). Since cast iron heats to temperatures well in excess of 350° (176°C) when you cook with it, you will essentially sterilize the cooking surface with each use.
If you end up with a real mess inside your pan that water and a scrub brush can’t fix, don’t succumb to the lure of detergent. There is a better way. Place the pan on the stovetop over medium-high heat. Put 2-3 tablespoons of oil in the pan and heat until the oil shimmers. Remove from the heat and put a generous handful of coarse kosher salt into the pan. With a wad of paper towels and a pair of tongs, scrub the inside of the pan using the salt as an abrasive. Rinse out the pan with hot water and repeat, if necessary, until the pan is clean.
If you just can’t wrap your head around the idea of no soap, you can use small amounts of a mild dish detergent, but you may have to repeat the seasoning process frequently. Whatever you do, never put cast iron in the dishwasher. Dishwashers, and the detergents that go into them, are not cast-iron friendly.
After cleaning your cast iron, it is always a good idea to wipe it down with a little vegetable oil to preserve the finish. Use just enough oil to give the pan a slight sheen but not so much that it feels greasy to the touch.
In the beginning, we recommend reserving a newly seasoned pan for greasier endeavors, such as frying chicken or bacon. Later, as the finish improves, you can venture out into other recipes. We also suggest you avoid using your pan for more acidic recipes such as tomato-based sauces. Acids will leach away that nice non-stick surface you worked so hard to create.
From time to time, it will help to repeat the seasoning process. Once around should be enough to refortify the surface. Re-seasoning 2-4 times a year, is a good strategy depending on how frequently the cookware is used.
Sometimes, something gets on the pan that no amount of scrubbing can eliminate, and it will become necessary to strip your pan’s surface with an abrasive and start all over again. Fret not, after a few re-seasonings, you’ll be on your way again.
- Aluminum foil
- Cast iron pan
- 1 tablespoon natural, unrefined sunflower or soybean oil
- Paper towels
- Line the floor of your oven with aluminum foil and pre-heat to 450°F (235°C).
- Clean and rinse the pan in warm water only, and towel dry. On the stove top, heat the pan over high heat until all the water has evaporated.
- Place a tablespoon of unprocessed sunflower or soybean oil in the still hot pan. Using paper towels and a pair of tongs, wipe down the inside of the pan until evenly coated. With a second paper towel, wipe out excess oil. The pan should have a thin even coat. Too much oil in the pan will form a tacky film, and you will have to strip the surface and start over again.
- On the center rack of the oven, place the pan upside down to allow excess oil to drip. Bake for 60 minutes. Turn off the oven and allow the pan to cool completely.
- If your pan was not pre-seasoned, you should repeat this process 3-5 more times.