Olives have traditionally been collected by hand, which is the surest way to protect both the olive and the tree itself. Modern techniques that use sticks or machines to shake olives loose from the trees may be faster and more profitable, but they often bruise the fruit, compromising the flavor. Collection of olives can happen earlier in the season when the olive is transitioning from its green color to a purple hue, or later in the season, once the olive has turned purple, or at the very end of the season, when the olive has become fully black in color.
The olive fruit is very high in oleuropein, an intensely bitter compound, and much less sugary than fellow drupes. While oleuropurin is safe, it is utterly unpalatable. Olives must be cured before they can be eaten whole. This is accomplished by soaking or packing the olives in salt, salt water, water or lye. The curing process leeches the bitterness from the fruit and leaves a plump, firm fruit.
The abundant oil present in the olive is not from the seed, but the fruit itself. Only about 1% of the oil comes from the pit. To extract the oil, olives are washed, and then pressed under mechanical pressure into a paste. This breaks open the flesh of the fruit, releasing the oils. The paste is then stirred, or malaxed, to allow the small droplets of oil to form larger drops, and then spun to separate the oil. This separation used to be accomplished with presses, common in production of other oils, but very few olive oils are still collected this way.
Modern Oil Collection
Most modern processes for collecting olive oil use centrifuges. The first spin in the centrifuge removes the oil from the wet paste of malaxed olives. The second centrifugation is done at a higher speed and it removes water and other solids from the oil. The oil is then left to sit and allow gravity to remove remaining impurities. A final filtration step may be used in creating the finished oil. Oils that are filtered are usually filtered either through fine paper or diatomaceous earth. Filtration does remove more of the sediment that might accumulate in the bottle, but it also removes some beneficial phenolic compounds and shortens the oils shelf life.
Olive Oil Varieties
It is these nuances of preparation that create the varieties of olive oil on the shelf. Extra virgin olive oil, referred to as EVOO, is extracted via one cycle of cold pressing. True extra virgin olive oil will be labeled by the North American Olive Oil Association (NAOOA), an independent group that tests the quality of olive oils.
Virgin olive oil is also from a first pressing, but it has a higher acidity. An EVOO has about 1% acidity, but a virgin olive oil may have up to 2%.
Other blends may include fino, which combines extra-virgin with some virgin oil, light, which has been filtered to remove most potential sediment, and pure, which is a combination favoring virgin mixed with some extra-virgin oils.
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