Why does the stainless steel inner pot have rainbow like stain after wash?
The discoloration on stainless steel cooking pot is called “rainbowing” which can be caused by exposure to high heat, cooking starchy things (e.g. rice, pasta) or even detergent staining after hand or machine wash. This is common in all stainless steel cookware. It’s normal and harmless. To clean the rainbowing discoloration, please follow the instructions on eHow. More cleaning suggestions from the British Stainless Steel Association.
