It's not the iron either - it's because if you cook too much with acidic liquids in cast iron you'll get some of the seasoning coming off and it may turn your f

It's not the iron either - it's because if you cook too much with acidic liquids in cast iron you'll get some of the seasoning coming off and it may turn your food blackish and unappealing. If you do a lot of cooking like that or don't have it properly seasoned you'll eventually have problems with going all the way through the seasoning and then you'll get rust. If you want to use cast iron for soups, stews, braises, chilis, etc. that you're going to be cooking a long time, get an enameled cast iron pan - that'll get you a lot of the heat retention but with a more durable (but not nonstick) finish.