Four to five kilos of olives are needed to produce just 1 liter of olive oil.
The olive tree begins to produce olives between the ages of 5 and 10 years, reaching maturity at about 20 years. After 100 to 150 years, its production begins to decline. The age of the tree influences only the quantity produced, not the quality.
The color of the olive is not connected to the variety, but to the stage of ripeness. The olives are green in the beginning, turning black as they ripen.
The olive tree blooms in the spring, with the fruit changing from a green color to black until the beginning of winter, when it is harvested.
The harvesting can be done by hand (“ordeño”), hitting the tree with a flexible pole so that the olives fall onto canvas covers placed on the ground (“vareo”), or by means of mechanical vibrations.
The olives collected are taken to the mill (almazara). They must be free of stones which could cause skin chafing or breakage. Also, heating should be avoided to prevent fermentation. To ensure the quality of the oil, the olive should be processed within 24 hours after being harvested.
For ventilation, the leaves are separated, and after undergoing a quality selection, the olives are washed in running water.
Immediately following, the fruit is squeezed (“molienda”), without separating it from the pit, until it becomes a paste, which is then whipped,
adding water if needed. Next comes the phase to separate solid from liquid, either by the traditional system (pressure), or by the continuous system (centrifuge). In either case, the temperature never rises above 35ºC (95ºF).
Traditional system, by pressure (“Non-continuous classical processing plant”): The ground paste is placed between pressing mats and is subject to pressure, to expel the oil must(mixture of oil and water).
The mixture is then poured into a vat or holding tank. This is allowed to rest so that gravity and different densities come into play, separating the oil from the water.
Continuous system, by centrifuge (“Continuous processing plant in three phases”): 1 liter of water is added per kilo of paste; it is then added to a horoizontal centrifugal machine, where the solid is separated from the oil must. The must is then passed on to a vertical centrifugal machine, where the oil is separated from the vegetable water.
Continuous system, by centrifuge (“Continuous processing plants in two phases”): Same process as above, but instead of adding water for the horizontal centrifugation, the vegetable water is recycled.
The continuous system, which is more and more widespread, presents advantages such as a higher production capacity, avoiding the storage of olives, and therefore improving the quality of the oil, and also better yield, cleanliness and hygiene.
Also, in the case of the continuous system in two phases, recycling the vegetation water provides a higher quantity of polythenols in the oil, natural protectors against oxidation.
The oil obtained is stored in cellars until it is ready to go to market, with ideal temperatures of between 15 and 18ºC (60-64ºF), low light, and isolated from agents which give off strange smells. The material in which they are deposited should be inert, glass-coated tile, or stainless steel–never iron or copper, which favor oxidation.
Air, light, and heat affect olive oil, so it should be kept in a closed container, at room temperature and out of direct sunlight.
As a natural product, and unlike wine, olive oil does not improve with time, so it is best used within a year.
Nevertheless, depending on the variety, a well-kept oil could last up to 18 months without losing its organoleptic characteristics.
The color of the oil does not determine its quality.