The raw olives are very bitter. They are "cured" mostly by bacterial fermentation. Later they may be alternately washed with water and packed with salt. The procedures vary a lot, and different varieties of olives get different treatment. The bitter chemical "oleuropein", a phenol compound, has to be broken down or removed. This is what the curing process does. Even so, olives still often do have a rather bitter taste. There is a variety called "Kalamata" which grows around 