Sometimes when I leave it on too long and it actually boils for a minute or two, there's a coffee ring around the inside of the stainless steel pot. Scrubbing it with a green dish scrub pad gets it off, then soap and water fixes the rest. I never really understood why that ring gets there, but it also gets there from the starch when I boil noodles. I figure it has something to do with electrons on the inside surface of the stainless steel pot losing their ionization or polarization or some sciency stuff. I haven't cared enough to even google it since I know how to fix it and I haven't died yet from it.