Q. Why is it when you steam or wilt fresh spinach you get that iron-tinny taste? How do you prevent it?
A. We’re guessing you have been cooking your spinach in an aluminum or unlined copper pan. Pans made of aluminum or unlined copper react with the sulfur compounds in green vegetables to create unpleasant odors and flavors, and destroy vitamin C, folic acid, and vitamin E. You should cook greens in stainless steel, enamel, or glass pans.
Gratuitously stolen from OChef