No olive should be picked from the ground, and likewise, all drupes displaying signs of olive fruit fly attack should be discarded, because the oxidation processes taking place in these fruits would cause the oil to be rancid.
The olives can be harvested by either shaking the trees, taking care not to damage them, or using pneumatic combs. The latter tools are usually made of plastic or wood, and when they are run through the foliage, they detach the olives from the branches. Since the crop should never touch the ground, nets are stretched under the trees, so that the olives fall directly onto them and do not get bruised or damaged. All twigs and leaves are then removed and the olives are immediately conveyed to the oil mill.