If the food is a plant then it could be immature. This means that it hasn't yet ripened to its prime, and it's not very tasty when eaten.
Inedible is another possible word. Inedible things can be non-food items such as a bed (you can not eat a bed therefore it is "inedible") or food items that aren't cooked or prepared where it is safe to eat, such as raw meat.
