During the ripening process olives change from green to violet then finally to almost black, and their pulp becomes rather soft. The ripening is progressive and very slow, especially when sunlight is not intense. Olives must be harvested when they are fully ripened and before the accumulated oil in the fruit starts to diminish. 
Olives are considered perfectly mature when they yield the highest amount of oil per acre. This parameter varies according to the characteristics of the location, the type of olive and the climate.
Very extensive olive groves are long-term, labor intensive operations. In fact mechanized harvesting is not very widespread, operations are totally manual or nearly so.
 

Hand picking: 
can be carried out principally on low plants, properly pruned and located on a plain. Every worker picks an average of 10 kg (22 lb) per hour. 

Raking: 
the fruit is collected with the help of a long wooden rake-like device which is dragged over the branches by hand causing the olives to fall onto nets spread on the ground around the tree; the raking action can be mechanized 

"Bacchiatura": 
this commonly used method consists in striking the foliage with long poles to cause the olives to fall on the nets spread on the ground below. There are poles available with mechanically operated tips, but they are not frequently used because they damage leaves and branches 

Permanent nets: 
these are spread out on the ground throughout the entire harvesting period to gather the olives that fall spontaneously. This method is suitable for dense olive groves located on slopes. However, the olives often remain on the trees too long to assure acceptable quality 

Mechanical shaking: 
the fruit is removed by shaking the trunk and branches with a mechanical shaker attached to the plant. This method requires trees with robust bearing. It is not frequently used.

Olive harvesting (photo: Jean Scotto) - Western Liguria, 1880
Under huge olive trees, using very long poles to beat the branches, the olives fell onto long, wide strips of cloth below. This operation occupied an enormous number of men and women over many months.