When I boil vegetables including broccoli the pot gets a water repellent-like residue at the water line that is very hard to remove. There is also residue similar to when cooking beans on the sides of the pots. This is in decent, newer stainless pots including the instant pot. My mother's older stainless pots don't seem to have this problem.
Does anyone know why this is and what is the best way to clean them? I wonder with time if it will become easier to clean. Or if the manufacturer coats them with something.