We are mainly using our vessel made of SS 316L to produce herbal extracts (thyme, marshmallow,...). After each production we are CIP cleaning it with either acidic of basic detergents and final rinse with demineralised water.
we noticed that the surface lost its shine and got different color. We thought it was rust, but cleaning with 10% H3PO4 didn't help. Any idea what it could be and is there any non-mechanical way to clean it?