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Cast Iron, Soap, and Received Wisdom

February 12, 2021

"Don't use soap on your cast iron!" It's a piece of advice so common that it turns up on TV shows and the internet has made a meme about it. It's advice I've given and heeded myself over the years, until one day I broke this first and only commandment of Cast Iron.

The Cardinal Sin

I had made hamburgers in my cast iron skillet and a bunch of crud stuck to the bottom of the pan. Nothing some elbow grease couldn't take off, but with kids hollering I didn't have time for elbow grease. So, I put the pan in the sink and cleaned it with soap and water. Then, nothing happened. The sky didn't fall, my pan didn't disintegrate, and it's seasoning, lovingly built up over years, was in perfect shape. I gave it a quick rub of oil after drying it on the warm stove, like I normally did, and all was well with the world. I do this all the time now, yet my skillet continues to persist. So, what was the source of the saying not to use soap on your cast iron? Was this even good advice to begin with?

How it was back then...

The best information I can get on where this piece of received wisdom comes from has to do with how soap used to be made. Apparently dish soap used to be very lye heavy and it had to be. Lye was the only option for soap at the time and the only way to get them truly clean. The only problem with this is that this lye heavy soap was terrible for human hands and terrible for the seasoning on your cast iron. Over time it would weaken the seasoning and have it strip off, giving an off taste to your food, having more food stick to it, and generally making your life more of a headache. It turns out, the "no soap on cast iron" advice was a very good practice back in the days of lye soap. So, what changed?

The way it is now...

The reason why the soap in my sink didn't kill my cast iron, is because it isn't technically soap. Soap cleans by being basic in a chemical sense, meaning the opposite of acidic. Something very basic can dissolve things just like something very acidic can and that's the short version of how soap used to clean pots and pans. What we use now is technically a detergent. A detergent clings to oils and fats on a molecular level rather than breaking them up like a basic lye soap does. Because your cast iron seasoning isn't really an oil anymore, modern detergent won't harm it. The received wisdom made loads of sense when it was originally made, but times changed and it's not really applicable anymore.

Trust but verify

The lesson I learned from all of this, is that received wisdom is very useful for giving me a starting point, but it can't be the ending point too. If I don't restate and verify my assumptions from time to time, I'm left basing my decisions on outdated information. While this doesn't always lead to a worse outcome, it can mean that I'm spending more effort to get things done than I need to, and effort isn't something I possess an infinite supply of.

So if you'd like to talk about some received wisdom you want to trust but verify, contact me. And in the meantime take a moment to check some of your base assumptions, you might be surprised what you find out.