Kitchen Myths

Facts and fiction about food and cooking, by Peter Aitken

You can’t wash cast iron cookware with soap

This myth seems to make sense—after all, you use fat to season cast iron and soap removes fat, case closed, right? It’s not that simple.

The seasoning layer on the surface of the pan is formed when the pan is heated while in contact with some fat or oil. This may happen during normal cooking or during a special seasoning process that many people use with a new pan. The result is a chemical reaction in which that fat polymerizes, meaning that multiple individual fat molecules join together to form larger molecules. It is these larger polymer molecules that bind to the metal of the pan and form the seasoning. And, guess what, the polymer is not dissolved by soap. So, it’s perfectly OK to use a mild soap on your cast iron if you are so inclined. Never use harsh detergent, put the pan in the dishwasher, or scrub with an abrasive, however, as these will take off the coating. You also should not cook acidic foods, such as tomato sauce, in a cast iron pan.

Of course, many people get their cast iron perfectly clean without soap, so there’s no reason to use it. The idea that soap will ruin the pan is, however, a myth.

Much new cast iron comes already seasoned. If not, it is likely coated with wax or shellac to prevent rusting, and you must remove this coating before seasoning. A good scouring with detergent will do the trick. Dry thoroughly, coat the entire surface, inside and out, with oil, and put in a 325 degree oven for about an hour. Let cool and wipe off excess oil and you are ready to cook. The best oil to use for seasoning is flaxseed oil. Lacking that, use lard or hard vegetable shortening like Crisco. Regular vegetable oils such as corn and peanut will work but are not as effective.

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8 responses to “You can’t wash cast iron cookware with soap

  1. tommy August 10, 2011 at 8:24 pm

    Wow, great. That was very informative. I will look forward to more good reading info. Thank you.

  2. Jen January 5, 2012 at 11:15 am

    I use mild soap all the time, so I’m glad to see this post. A couple of questions, though:
    1) what about soap is so different from detergent and putting cast iron in the dishwasher that the former won’t remove the seasoning layer but the latter two will?
    2) I’ve also heard that the supposed reason not to use soap on cast iron is that it soaks into the pan? Any info on this that you are aware of?

    • kitchenmyths January 5, 2012 at 11:35 am

      Detergents are different from soap. They are harsher and that’s why they clean better. But soap is all you need for some tasks, like washing your hands or cleaning a cast iron pan. About the soaking, I have not heard this.I It seems unlikely given that the seasoning that coats the pan is a pretty good barrier (this is why a seasoned cast iron pan won’t rust, for example).

      • Sean February 16, 2012 at 10:08 am

        Related question:
        I make bacon and eggs for breakfast almost every morning using a run-of-the-mill nonstick frying pan (Paula dean brand, I believe). I never wash it after I use it (though I do drain off the excess bacon grease) bc the fat helps prevent the next batch of bacon from sticking. When my wife insists on washing it, she uses dawn dish soap, and I can smell and taste the soap in my breakfast the next day. What causes this? Is it normal for a nonstick pan to do this?

        Thank you for your help.

      • kitchenmyths February 16, 2012 at 10:44 am

        Hmm, curious situation you have! It is definitely not normal for a nonstick pan to taste of soap (I assume it is being rinsed well), but it is also not normal for bacon to stick to the pan. This makes me wonder if perhaps the nonstick coating is worn out, causing the bacon to stick and absorbing the dish soap. All I can suggest is a new pan. Cast iron would be ideal for this.

  3. jacqueline April 23, 2014 at 7:51 am

    Also — always remember to have any pan thoroughly heated prior to adding bacon or any food item. Hot pans should prevent sticking as well. And if the pan tastes of soap – its not been rinsed well .. plain and simple :)

  4. Mehul Teli June 13, 2014 at 3:16 am

    Another very common myth about a cast iron fry pan is ‘Metal Utensils Scratch the Surface’. In reality, light scraping while cooking polishes the iron, allowing the seasoning to adhere better to the pan. It’s actually good practice to promote this process.

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