This is an old, old topic of discussion on sci.chem--why do metals smell, especially when wet and especially when the surface is disturbed. There are a large number of hypotheses--from free metal atoms, free metal oxide, hydroxide or carbonate molecules, small metal or metal oxide-hydroxide-carbonate clusters, metal chlorides (from Cl2 in drinking water--although you get a similar smell in rain water), to volatile metal compounds like metal hydrides, and even things peripherally related to the metal, like reaction products of Cl2 and organics in drinking water that are catalyzed by the metal or its ions or salts. In the case of stainless steel, there are a number of alloyed metals, so the possibilities are multiplied. I don't know if there's consensus, but the FAQ might have something to say. I haven't looked at it recently--is Bruce Hamilton still maintaining it?
Those stains clearly came from stuck noodles that were not removed quite as quickly as the rest of the cooking water. My guess might be reaction with partially soluble sulfur-containing proteins in the pasta, or possibly reaction with salt dissolved in the pasta and cooking water that was held on the suface by the stuck pasta after the rest of the water was drained. Both represent a disturbance of the formerly polished suface of the pan. Not sure how to remove-prevent the stains--maybe silver polish. That, or using an aluminum or Teflon-coated cookpot.
Eric Lucas
