Olive oil: the king of the Mediterranean cuisine
Where does olive oil come from? The origins of olive cultivation are coincide with those of the Mediterranean civilisation. The first olive groves were cultivated in Syria and Palestine and, around 1000 BC, it spread to Italy, where optimal conditions (i.e. a mild climate, the presence of water and of rich soils) favoured its growth. There are approximately 1,000 olive species in Europe.
Olive oil is the only fundamental food that comes from a fruit. It has been obtained for fifty centuries by pressing the olives, separating the oil from the water of vegetation. The olive fruit (Olea europea) is a drupe, a fleshy fruit that contains a single seed inside the pulp in a woody endocarp. The oil is contained mainly in the mesocarp of the fruit, which is formed during maturation, when the colour of the drupe changes from green to purplish black.
The harvesting of olives follow a seasonal pattern and, depending on the year, it can continue for months, from late summer until late winter. The harvesting techniques vary and range from hand detachment through small rakes that are passed through the branches, to the use of mechanical tools. A widespread technique then employs the use of nets put under the olive tree or at some distance from the soil. The degree of ripeness at the time of harvesting varies according to each specific tradition: in Corsica the olives are harvested at full maturity, while in Tuscany and Sardinia they are harvested before. In the latter case, the presence of some olives that are not yet ripe, along with others having a higher degree of ripeness, gives the oil a typical spicy flavour.
The quality of an olive oil depends on many factors: the cultivar, the state of health of the olive tree and of the olives at the time of harvesting, the technology used in the production, harvesting and extraction, the storage conditions of the oil itself (light intensity, temperature).
Olive oil is extracted from the olives mainly using two systems:
- classical pressure method;
- modern centrifugation method.
The phases of extraction by pressure include a cleaning phase to remove the soil and any foreign matter that is attached to the olives. This step is followed by the milling, through which the cellular structure of the olives is broken and the seed is crushed. This step generates the olive paste. The latter is then mixed by a process known as ‘kneading’. Mechanical extraction is then carried out using hydraulic presses. The oily liquid is collected at the bottom, and what remains as a residue of the pressing is called “pomace”. Finally, the oil is centrifuged (with the aim of removing the water from the must) and filtered to make it clear. When the oil is extracted by centrifugation, the latter is applied right after the kneading phase and repeated twice to remove all impurities.
An additional technique involves washing the olives in water at 70°C in order to reduce the bitterness of the oil. This practice has a commercial value and makes the oil more attractive to those consumers who do not like the bitter taste. However, this process reduces the amount of both vitamins and phenols, especially oleuropein, which causes the bitter taste typical of some olive oils. This is the main reason why cold pressed olive oil is usually recommended, although higher temperatures during the extraction also imply greater oil yields.
Olive oil is considered edible if it contain less than 3.3% acidity by weight (expressed as the content of free oleic acid) and, after organoleptic examination, it is not characterised by any of the following: disgusting odors such as rancid, putrid, smoke, mould, worm (I can’ t imagine how it may be!) or other similar bad odours. In the next post I will describe more in detail how olive oils are classified.