Reader Rikki writes:
I know this probably isn’t your area, but I’m trying to season a cast iron pan. The pan maker says I should use low heat to season it, but just about every other seasoning article I’ve seen on the web says very high heat is the thing. Can you tell me: what’s the difference and which method should I use?
Rikki, just because I’m a baking blogger doesn’t mean I can’t flap my fingers for a while on this general cooking subject. It’s pretty interesting stuff! As you surely know by now from your readings, seasoning is the process by which porous die-cast metal pans are transformed into smooth, virtually non-stick cooking implements. In the old days people didn’t think much about seasoning since it just happened over time with use. Today home cooks take a more clinical attitude toward seasoning. As you mentioned, pan manufacturers usually provide instructions on how to season a new pan. The typical procedure calls for a fat of some kind (usually solid) to be applied to the pan in a thin layer, then the pan is baked in a low (300 degree) oven for about an hour. Done correctly, the process yields a slick surface which, if the pan isn’t scrubbed out with soap, works very nicely.
But how exactly does seasoning work? It all has to do with the breakdown of fat molecules. Some of you may recall from previous posts on fats that fat molecules are “E”-shaped: three long fatty acid molecules attached to a “backbone” of glycerol. Heat them though, and they begin to break into pieces. The individual fatty acids come loose from the backbone, at which point they’re free to bond with whatever type of molecule catches their fancy. If they happen to be near iron, they’ll bond to that, with their polar end down and their “fatty” end up. The end result for the pan is that all the tiny pores in the metal get plugged up and the surface becomes slick.
Many cast iron aficionados kick the whole seasoning procedure up a proverbial notch by employing a liquid fat (oil) and high heat. This method not only breaks the fatty acids off their glycerol backbones, it breaks the fatty acids themselves into pieces — pieces which, in the presence of metal and oxygen, rearrange themselves into chains known as polymers. These polymers inter-weave with one another to create an incredibly hard and dense plastic-like film. If you’ve ever spent hours trying scour blackened drips of burnt fat off the exterior of a sauté pan, you’re familiar with the stuff. You find it on the outside of pans and on cooktop surfaces because that’s where the big heat is.
To create a polymer film on the inside of a pan you need oil (because less saturated fats make harder polymers) and an oven temperature of 500 degrees or more. It’s a stinky, smoky process and one that in my opinion isn’t strictly necessary. To my mind the best way to season a cast iron pan is to employ the low-heat method, then use it as often as you can being mindful of soap at cleaning time. But that’s just me. For more on high-heat seasoning, see this very interesting post here.