Olive oil is made from the olive fruits when they are six to eight months old, mature and approaching their maximum oil content, and just beginning to turn color from green to purple; fully ripe fruits develop less of the valued green aroma. The olives are cleaned, coarsely crushed, pit and all (sometimes along with some leaves from the tree), and finely ground into a paste to break the fruit cells open and free their oil. The paste is mixed for 20–40 minutes to give the oil droplets a chance to separate from the watery mass of olive flesh and coalesce with each other (this step is called “malaxation”). Then the paste is pressed to squeeze both oil and watery liquid from the solids. More oil, but of lesser quality, is extracted by pressing repeatedly and by heating the paste; oil extracted in the “first cold pressing” is the most delicate and stable, and most likely to yield “extra virgin” oil (below). Finally, the oil is separated from the liquid by centrifuge or other means, and filtered.