The adjective inedible is good for describing a food that cannot be eaten, like your grandmother's burnt toast, or an object that shouldn't be eaten, like your snow boots.
Some things are literally inedible, like your dining room table or a cast iron skillet, while others are described as inedible in a more figurative way: "I can't stand cilantro — now this taco is totally inedible!" The word has been around since the early 1800s to mean "unfit to eat," combining the Latin prefix in, which means "not" or "the opposite," with edibilis, "eatable" in Late Latin.