How Olive Oil is Made

Harvesting
Production of olive oil begins with the harvest, the timing of which is a major factor in the final product. The picking of the olives starts as early as September, when the olives are underripe and still green. They yield little oil, but their flavor is intense. These oils have the longest shelf life and are richer in sensory properties such as flavor and aroma. Oil from olives harvested early has a low percentage of acid and the characteristic deep green color typical of the Tuscan oils.

Harvests generally come between early November and let December. Some olives are harvested in the red-ripe stage and blended with the earlier harvested oil to create a more balanced product. In general, the oils from fruit harvested in the black-ripe stage are of inferior quality, containing more acid and less flavor.

The youngest green olives are hand-picked off the branches, whereas riper olives can be beaten or shaken down and collected beneath the trees. Since olives are delicate, the best oils are made from olives that are picked by hand or by machines that do not beat or bruise the fruit.

Milling and Pressing
Olives should be crushed within the first 24 or 36 hours of picking. If left to wait, the level of acidity rises, creating olive oil of poor quality. Just before being crushed, the olives need to be run through a washer to eliminate any remaining impurities. Generally the olives are crushed whole, without prior stoning in roller mills.

The simplest method of crushing olives is with a varying number of granite millstones. The olive paste obtained through milling is layered on nylon, or natural fiber, mats, called "fiscoli," which are stacked high, with metal disks between them. These mats of olive pulp are then subject to a great deal of pressure from a screw or hydraulic press. The liquid produced by the pressing drains through the mats and cylinder and is collected for the final separation.

This liquid is made up of water and oil that need to be separated from one another. The liquid is put through a centrifugal separator, where the rapid spinning eliminates all remaining water and all of the impurities from the oil.

After centrifugation, oil appears amber in color, with an opaque quality—a characteristic feature of superior oils. The more acidic the oil, the clearer and brighter it appears, and the worse it is for your health. Oils processed by anything but centrifuges and mechanical or hydraulic presses cannot be called virgin olive oil.