Myths about cast iron are some of the things I run into as a trainer of scout adult leaders. Which is a bit of a shame. If you understand the chemistry, then care is easy.
The basic chemistry can be summarized as follows
- The black coating is Iron Oxide (Fe3 O4 and others).
- Iron Oxide doesn’t react easily with water and sugar.
- Iron Hydroxide (Rust, Fe(OH)3 and others) reacts easily with water and sugars
- Iron Hydroxide can be converted with heat, a carbon source and a somewhat anaerobic environment, into iron oxide
I am being a bit simplistic here, but it’s accurate enough.
The recommended care cycle for cast iron then makes sense. After cooking, use water to clean the debris. Really stuck on crud can be removed with boiling water. After the pot is clean, coat it in oil and heat.
What’s going on?
You’re removing the debris, and then regenerating a layer of iron oxide. That simple.
What happens when food sticks?
Sugar in the food reacts with trace amounts of iron hydroxide on the pan’s surface. But, you say, “Meat doesn’t have sugar in it and meat will stick?” The answer is that meat, at least from complex critters (Eucaryotes), is covered in sugars as part of how cells recognize and communicate with each other. Sugars contain alcohol groups (Not ethanol – you won’t get drunk from eating them) which interact with iron in much the same way as water. So you get an Iron-sugar chemical compound, which after pyrolysis (a fancy way to say burning) becomes a sticky mess.
So how do we stop the sticking?
Heat the pan first. This drives off much of the remaining water, converting the trace amounts of hydroxide back to oxide. A coat of oil also helps because it keeps the sugars in the food from contacting the metal surface.
Why shouldn’t I use soap?
First, I will remove some of the protective oil and expose the more reactive iron to water. Thus generating hydroxides. I see this when I make a white gravy (Milk based) where the natural detergents in the milk strip some of the oil away. There’s usually a thin coating of the brown hydroxide after I’ve cleaned the pan. Coating the pan with oil and heating returns it to normal.
Second, the detergent mixes with the oil. You won’t necessarily taste it, but detergents have chemical groups that attract water and sugars. Therefore the detergent helps the food to stick.
Note that I haven’t given highly specific temperatures. Things like “sandblast and put in a 305 degree oven for exactly 45 minutes.” That’s because they are not necessary. Keep it dry, keep it oiled, and avoid detergents. Remember you’re trying to build up a layer of iron oxide and you’ll be fine. Not only that but your great-grandchildren will thank you when they use your pan.