Olives

The olive is a Mediterranean stone-type fruit of the olive tree (Olea europaea). The colour of unripe olives is green and that of ripe olives is black or violet/brown. Because of their bitterness, raw olives are not palatable. To make them edible, they should be repeatedly immersed in water to remove the bitter substances. "Real" black olives are fully ripe green olives. Commercially available black olives are often green olives which have been blackened using ferrous gluconate.