The olive fruit is a drupe. It has a bitter component (oleuropein), a low sugar content (2.6-6%) compared with other drupes (12% or more) and a high oil content (12-30%) depending on the time of year and variety.
These characteristics make it a fruit that cannot be consumed directly from the tree and it has to undergo a series of processes that differ considerably from region to region, and which also depend on variety. Some olives are, however, an exception to this rule because as they ripen they sweeten right on the tree, in most cases this is due to fermentation. One case in point is the Thrubolea variety in Greece.
Oleuropein, which is distinctive to the olive, has to be removed as it has a strong bitter taste: it is not, however, pernicious to health. Depending on local methods and customs, the fruit is generally treated in sodium or potassium hydroxide, brine or successively rinsed in water.