text: why do we taste metal when we put a metal key in our mouth? chemical science you are not exactly tasting the metal, as metal molecules are tightly bound. unless you are eating a metal that reacts too easily, like sodium.  metal keys are usually made of iron, so you are actually tasting impurities like rust mixed with dust, that you think is the metal.  try tasing a gold or platinum thing that is totally clean. your tongue will probably feel cold, but ther won't be any taste.