How is olive oil made?

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Olive Oil Factory

Olive oil is extracted from the fruit of the olive tree, the olive, using mechanical methods, without adding chemicals, and is true fruit juice. Traditionally, oil extraction systems carried out the process in three phases: milling, pressing, and decanting.

First, the olives are harvested from the olive trees, by beating or other mechanical means, always trying to ensure that the olives do not touch the ground and do not damage the olive tree. The olives are then moved to the olive mill’s receiving yard. It is important that this transfer be quick, within a few hours, since olives begin to “die” the moment they leave the tree.

Once at the olive mill, the olives are cleaned and placed in the mill, for grinding and blending, thus releasing the oil. The resulting paste then passes to centrifuges to separate the liquid from the solid.

Finally, the oil obtained passes to decanters to further remove olive residue. The olive oil thus obtained is stored in special tanks, inert and at controlled temperature, awaiting bottling.

This process is very similar to how it was done in ancient times. Indeed, during the Roman Empire, stone mills were already used to split and peel the olives, and the resulting paste was then pressed to extract as much oil as possible. What has evolved over time is the method of pressing the olive paste.

Olive oil production process

Olive oil is the oily juice obtained solely from the fruit of the olive tree (Olea europea L.) without solvents.

Of all these, the most important is Virgin Olive Oil, obtained exclusively by mechanical or other physical means with no other treatments than washing, decantation, centrifugation, and filtering.

Oil makes up 15-25% of the olive and is found in the vacuoles within the olive cells. Therefore, its production consists of separating the oil contained in the fruit from the solid components and the vegetation water.

Washing and Weighing

When the olives arrive at the oil mill, dust and other elements such as leaves, soil, stones, and branches must be removed. These processes are carried out with automatic machines and fans, and they are washed in rotating drums, which separate the heavier materials. After washing, the olives are weighed to determine the quantity of clean olives contributed by each partner.

Extraction Processes

Two processes are used to extract olive oil: the horizontal centrifuge (Decanter) of the three phases present in the olive (oil, vegetation water, and solids); the following (two-phase) separates the oil from the remaining components present in the fruit (solids and vegetation water). In some places, the traditional process is still used, in which the oil is obtained by pressing.

Grinding, Churning, and Decanting

The olives are crushed in mills to break the pulp cells and allow the oil to escape from the vacuoles, forming larger drops that can be separated from the other phases. Generally, in this traditional process, the olives are crushed in stone mills.

Once the olives are crushed, the resulting paste must be slowly churned for a few minutes with paddles that continuously move the paste in semi-cylindrical or hemispherical containers. Thus, the main objective is to increase the size of the oil droplets so they can be separated more easily.

Pressing and blending the paste produces a liquid containing olive oil, vegetable water, and a small amount of solids. Allowing the liquid mixture obtained during pressing to rest ensures that the oil remains on the surface because its density is lower than that of vegetable water.

The two-phase process has a higher yield than the three-phase process. This is because no water is added to the paste, resulting in almost no spillage. In fact, only a small amount of wash water is added, avoiding the environmental problems of evaporation ponds.

The quality of the oil produced is superior to that obtained in the three-phase process, due to the high amount of polyphenols and/or diphenols, which means that the oil is more stable during storage.

StorageOlive oil

Olive oil storage tanks must be constructed from completely impermeable and unassailable materials. Thus, the material used must have greater inertia than the oil itself, so that it does not absorb undesirable odors and flavors and does not dissolve substances that could contaminate or cause oxidation (the presence of metals).

The tank must be protected from light and air, factors that accelerate the deterioration of the product. It must also maintain the oil at a nearly constant temperature (around 15-18°C), avoiding sudden changes. In fact, low temperatures can cause the oil to freeze, and high temperatures contribute to its oxidation. Currently, stainless steel tanks are used, usually 50 tons.

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