I have a small cast-iron pan that I use a few times a month, sometimes more, sometimes less. Most advice about how to season a cast-iron pan involves lightly oiling and wiping it down, after it's been cleaned, before putting it away. This seems to assume that the pan gets used every few days. Since I don't use it very often, my concern is that any oil that remains on the pan might go rancid before I use it the next time, and that it will affect the flavour of whatever I cook. Is this something I should actually worry about? How do other people treat a cast-iron pan that only gets occasional use?
My (carbon steel) wok is used with that sort of frequency and doesn't go rancid. What I do is (you may want to modify a little for the fact you're on cast iron):
- Rinse and dry it.
- Get it fairly warm.
- Pour in a little oil (sunflower as that's what I mainly use).
- Swirl/wipe the oil over the surface.
- Heat until I think it starts to smoke; turn off the gas.
- After a few seconds wipe of the excess with a paper towel.
- After a few minutes wipe it off again as some oil will have magically appeared
- Heat until it just starts to smoke again (fairly slowly to allow the heat to even out).
- Allow to cool before putting away.
Now this isn't a very hard seasoning, but it does a good job of stopping the pan from rusting and stopping food from sticking next time it's used. The final amount of oil is very small, which helps.
I've been using the same cast iron skillet since 1989 (yep, that long). After I cook in it, I do a thorough rinse with hot water and a scrubby of some sort. No dish soap. No scouring pad. I typically have a film of oil remaining. I put the skillet in the oven (center rack, upside down) and set the oven to 350F. Once it is preheated, I turn the oven off and let the skillet dry in the oven overnight. This routine has kept my skillet in good condition for decades. I'm sure someone will say that I'm not doing it "right", but the method is simple and it has worked for me over and over again.