I had brewed my first batch last week and used a new Bayou Classic SS kettle. After cleaning it thoroughly, I noticed that there is some sort of stains or oxidation at the waterline and above. Almost like the bubbled wort on the side made the marks. Is this normal for kettles? Can I clean it off, or should I even worry about it? When you run your fingers over it it doesn't feel like debris is caked on. I tried searching about this problem but couldn't find any results of the same.