Some types of steel (warm rolled, I guess) come with a black coating, which is obviously a result of the manufacturing method. As far as I can tell, according to Wikipedia, this is stuff like Hematite or Magnetite (i.e., iron oxides), and it is pretty tough - i.e., not something that will flake off etc., but it sticks where it is and is also a pretty good rust preventer, as long as the piece stays rust-free. As far as I can tell, one way to remove it is by giving it a good long soak in readily available citric acid, although I have not tried it yet and don't know if it is completly "shiny" afterwards (I assume not).
I am currently working on a roasting drum, which obviously does come in contact with food (coffee beans, in my case). I am not too squeamish in this regard, but does anyone know if that black coating is a health problem, or if it is completely harmless? The roast drum (which is freshly bought and looks pretty pristine, i.e., shiny black, not scaley-flakey) will obviously be washed down as best as possible to get rid of any other possible residues. Also, the first few roastings will be thrown away anyways since it is unlikely that the temperature will be gotten to the right point from the get-go (I have experience with other roasters of the kind, this is just the newest generation for me ;) ).
I found explicit sources that say at least Magnetite is non-toxic (medicinal uses), FeO and Fe2O3 are FDA-approved in cosmetics, Fe3O4 is used in medicine, and I never saw any remark anywhere that iron oxides / rust is are unhealthy (no, I do not suggest drinking the PCB etching stuff

). No-non-stick (traditional) iron pans don't pose health problems, rusty barbecue grills have been spotted in the wild, etc. Last but not least, as only the surfaces of the beans are actually in contact with the metal, and then the water is only pressed through the ground stuff, I guess anything that rubs off will be in homeopathic dilution anyways.
Anyone got anything else to add to my thoughts, to keep me a long-lived healthy coffee guzlling mad modder?