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Kitchen Myths
Facts and fiction about food and cooking, by Peter Aitken
You can’t wash cast iron cookware with soap
Posted by on March 30, 2011
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.
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.
Kitchen Myths 
Wow, great. That was very informative. I will look forward to more good reading info. Thank you.
You are most welcome!
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?
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).
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.
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.
Sean, you may just be really sensitive to smells/tastes. I am and the people around me think I am crazy except my mother who I got this from.
I can taste a lot of peoples perfume and air fresher.
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 🙂
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.
DOn’t you create bacteria by NOT using soap to take off bacon grease for instance? It seems wrong to leave greasiness on. I just bought a seasoned Cast iron pan but it got washed with a metal scrubby and then was not dried afterwards….this made it have rust spots. What was done wrong? Also, why not have tomatoes in a Cast Iron? THank you so much!!! I have never used CI before!
You can remove greasiness with salt and a scrub brush and you’re suppose to kill the bacteria by heating the pan over the stove after you wash. While heating it, you put on a light layer of fat (I use coconut oil) to prevent rust. This is all I do to my pans and I don’t get sick. Modern day people are ridiculous germ a phobes, we’ve lost common sense. I almost through out milk I left out for a few hours but decided to google it and there were people who said “we use to keep (non pasteurized mind you) milk in the pantry for days that we milked from cows before it went bad.” After reading this I gained the courage to taste the milk (milk turns to buttermilk before getting too bad) and it tasted perfectly fine albeit warm and I put it back in my fridge and saved $4. -I’m not saying medical advances are stupid and don’t get vaccinated.