Iron spoon is used to cook sweet potato millet porridge. Why does it turn black? Can I still eat?

Well, did you put alkaline noodles in the porridge? The iron spoon in life turns black, which generally reacts with oxygen (iron oxide is black), or the iron spoon is coated with aluminum, which is very easy to oxidize, especially when it comes into contact with acidic, alkaline and salty substances, which will accelerate oxidation. It doesn't matter if all the active metals turn black, as long as you don't eat them with an aluminum spoon.