It's kind of a catch 22. If you use abrasive scrubbing to remove it, you put deeper scratches into the stainless which provides a better foothold for the beer stone in the future. I think I might experiment a bit by putting a high polish on a smaller 3" circle on the bottom of the kettle just to see if it cleans up easier. I've had luck with an overnight soak in double strength starsan.
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