I scrubbed my new SS kettle down pretty well with a mild dish soap/water solution when I got it, and the sponge came off clean. I rinsed very thoroughly to get any dish soap residue off. When I filled it with water for my first brew, the water smelled a little metallic. After brewing, I did another cleaning, and the sponge came away with some black residue. Also noticed the same black residue on the end of my (wooden) mash paddle. I'm hoping it's clean by now and my first batch wasn't affected, but I'm a little nervous.