From Olive to Oil: How Extra Virgin Olive Oil is Made

In the extra virgin olive oil tasting guide, we saw how to recognize fruity, bitter, and spicy notes, and how to distinguish a quality oil from a defective one. But where do these characteristics come from? They depend almost entirely on what happens before the oil reaches the bottle: from the olive harvest to the oil extraction, each stage of the production process leaves a precise imprint on the final product.

In this article, we follow the entire journey — from the field to the mill — and see how an extra virgin olive oil is born, what choices make the difference between a mediocre oil and a quality one, and how we work at Oleificio Paolo Demuru in Ilbono, Ogliastra.

Why the production process determines the quality of the oil

Extra virgin olive oil is not "produced" in the industrial sense of the term: it is extracted. Olives already contain oil inside them — the miller's task is to extract it as intact as possible, preserving all the aromatic compounds, polyphenols, and vitamins that make an extra virgin what it is.

Every mistake along the chain — olives harvested too late, poorly stored, processed with delay, extracted at too high temperatures — results in an oil with fewer aromas, fewer polyphenols, and, in the worst cases, sensory defects recognizable as rancid or fermented.

This is why the complete supply chain — from the field to the mill, all under the same control — is the most important condition for ensuring consistent quality.

The olive harvest: the most critical moment of the entire process

Harvesting is the phase that most of all determines the quality profile of the oil. Two variables are decisive: when to harvest and how to harvest.

The right moment: "invaiatura" (veraison)

Olives are not harvested when they are completely black and ripe. The optimal moment is invaiatura, which is when the skin begins to change color from green to purple, but the pulp is still largely green. At this stage, the olives have the maximum content of polyphenols and yield oils with an intense fruitiness, pronounced bitterness, and spiciness — characteristics that in our previous articles we saw as indicators of quality and freshness. It must be said that the intensity of each also depends, and decisively so, on the olive variety: some cultivars are genetically predisposed to yield more fruity oils, others more bitter, and still others with a particularly pronounced spiciness. The harvest time amplifies or attenuates these characteristics, but does not create them from scratch — the base is always the variety.

Waiting longer is only advantageous in terms of yield: riper olives produce more oil per kilo of milling. But that oil will be flatter, less aromatic, with fewer polyphenols and a shorter shelf life. This is the choice many industrial producers make. It's not ours.

In Ogliastra, the harvest generally begins between October and November, with some variations related to the year's climatic trend. The Ogliastrina cultivar — the native variety at the base of our DOP Sardegna extra virgin olive oil — requires particular attention to timing: too early a harvest can limit the yield, a late harvest compromises the intense fruitiness which is its main characteristic.

How to harvest: by hand and with mechanical aids

There are different harvesting methods. We use a mixed approach: hand harvesting in areas where the terrain conformation or plant arrangement does not allow the use of equipment, and mechanical aids — vibrating rakes and shakers — where it is possible to work more quickly without compromising the quality of the olives.

Hand harvesting is slower and more expensive, but it ensures that the olives arrive at the mill intact, without abrasions or crushing that would initiate oxidative processes already in the field. Modern mechanical aids, used correctly, allow for higher harvesting speeds while maintaining a very good level of fruit integrity.

What matters, in both cases, is that the harvested olives are transported in rigid, aerated crates — never in sacks, where the weight of the fruit on the olives below initiates fermentation processes — and processed within a few hours of harvesting.

From field to mill: hours matter

The least possible time should pass between harvesting and milling. The ideal is to process the olives within 12-24 hours of harvesting, storing them in thin layers in cool, aerated environments.

Every extra hour is an hour in which enzymatic and oxidative processes degrade the quality of the oil that will be obtained. Olives stored for days in piles or sacks develop internal heat due to fermentation and produce oils with defects of musty, sludge, or mold — those defects that we learned to recognize in the tasting guide.

Having the oil mill on the farm, as in our case, eliminates this problem at the root: from harvesting to milling, the distance is minimal and control is total.

Defoliation and washing: preparation before milling

Before entering the mill, the olives go through two fundamental preparatory stages often overlooked in the description of the process.

Defoliation removes leaves and twigs left during harvesting. It is not just an aesthetic issue: excessive leaves in the paste can give the oil unpleasant herbaceous notes and alter the aromatic profile. A small percentage of leaves (around 2-3%) is, however, tolerated and by some considered positive for the chlorophyll contribution.

Washing with clean water removes soil, dust, copper residues, and other contaminants from the surface of the olives. It is a brief but important step for the cleanliness of the final product and for the protection of the machinery.

A final often underestimated element is the cleanliness of the mill. Residues from previous processing — oxidized pastes, old oil deposits — are one of the most common causes of sensory defects in oils, particularly rancid and fermented. A clean mill, with sanitized machinery between one processing and the next, is a necessary condition for producing quality oil, not an option. It is one of the aspects over which those who have the mill on their farm can exercise direct and constant control.

Milling: breaking the olives to release the oil

The first real processing phase is milling, which is the mechanical breaking of the olives to form a homogeneous paste of skin, pulp, and pit.

The most common systems in modern oil mills are the hammer mill and the knife mill. The first uses high-speed rotating hammers that crush the olives in a few seconds, producing a fine and homogeneous paste that promotes the extraction of polyphenols and tends to yield oils with a more intense fruitiness. The knife mill works with rotating blades that cut the olives more delicately, producing a slightly coarser paste and allowing greater control over the degree of breakage. Both systems are valid: the choice depends on the olive variety, the quality objective, and the characteristics of the mill.

The choice of milling system influences the final profile of the oil, but it is only one of many factors at play.

Malaxation: the least known but fundamental step

After milling, the olive paste is transferred to malaxers, tanks equipped with rotating blades that slowly mix the paste for 20-40 minutes. It is the least known step to the general public, but one of the most important.

During malaxation, two fundamental things happen:

The oil droplets dispersed in the paste aggregate into larger drops through a process called coalescence, making subsequent mechanical separation possible. Without malaxation, the oil would remain trapped in the paste and could not be effectively extracted.

At the same time, heat and contact with air during malaxation can degrade aromatic compounds. This is why temperature is critical: cold malaxation takes place below 27°C and preserves aromas and polyphenols. Higher temperatures increase oil yield but compromise sensory and nutritional quality.

The indication "cold extracted" that you find on the labels of quality oils refers precisely to the fact that both malaxation and extraction took place below this temperature threshold. It is a precise regulatory requirement, not a generic indication.

Extraction: separating oil from water and pomace

After malaxation, the oil must be separated from the solid part (the pomace, composed of skins and pit fragments) and the vegetation water.

The most common system today is the centrifugal decanter: the paste is fed into a high-speed rotating drum which, by exploiting the difference in density between oil, water, and solids, continuously and efficiently separates the three components.

There are two main configurations:

Three-phase system — adds water to the process to facilitate separation. It produces cleaner oil but partially dilutes water-soluble polyphenols, which are lost in the added water.

Two-phase system — does not add external water. It better preserves polyphenols and organoleptic characteristics, produces less wastewater, but generates wetter pomace. It is the preferred system for high-quality oils.

After the decanter, the oil generally passes through a vertical centrifuge to remove the last traces of water and fine impurities before being stored.

Storage: the last risk not to underestimate

Freshly extracted oil is at its peak quality. From this moment on, a race against time begins: light, heat, oxygen, and heavy metals are the main enemies.

Professional storage takes place in stainless steel tanks, at controlled temperatures, in a nitrogen or carbon dioxide atmosphere to eliminate contact with oxygen. These precautions slow down oxidative processes and allow the oil's organoleptic characteristics to be maintained until bottling.

This is why the production date — not the expiration date — is the most important information on a quality extra virgin olive oil label. As we saw in the article on how to read the EVO oil label, an oil with a distant expiration date but produced two years ago is not as valuable as a fresh, vintage oil.

From the mill to the bottle: the complete supply chain

The journey we have described — from harvesting in the fields of Ilbono, through our oil mill to bottling — all takes place under the same control. There are no intermediaries, no changes of hands, no waiting between one phase and the next.

This is why the complete supply chain is not just a marketing slogan: it is the technical condition that makes it possible to make quality choices at every step, from harvesting timing to malaxation temperature, without having to make compromises dictated by external logistics.

The result is what you find in our extra virgin olive oils: oils that tell the story of the Ogliastra territory, its native cultivars, and the work done at every stage of production.

FAQ: frequently asked questions about extra virgin olive oil production

How many olives does it take to make a liter of oil? It depends on the variety, the harvest time, and the vintage, but on average it takes between 4 and 6 kg of olives to produce 1 liter of extra virgin olive oil. Olives harvested at "invaiatura" (less ripe) require more kilos but yield a qualitatively superior oil.

What is done with the pomace? Pomace — the solid residue remaining after extraction — still contains small quantities of oil that are recovered with chemical solvents in industrial pomace mills, producing olive pomace oil. It is not extra virgin and should not be confused with it. The remaining part is used as biomass for energy or as an agricultural amendment.

Is new oil always better than old oil? Immediately after extraction, the oil can have very marked, almost aggressive, "herbaceous" and pungent notes. With a few weeks of natural decantation, it stabilizes and reaches optimal balance. From that moment, if well stored, it maintains its characteristics for 12-18 months. After that, it gradually begins to lose aromas and polyphenols.

What does "first cold pressing" mean? This is a designation partly superseded by modern regulations, but still widely used in marketing. It means that the oil was extracted mechanically (not chemically) and at a controlled temperature below 27°C. Today the correct term is "cold extracted" or "cold obtained," and it is regulated by the EU.

Does the color of the oil indicate quality? No. The color depends on the olive variety, harvest time, and filtration level, not on quality. An intense green oil is not necessarily better than a golden one. As we saw in the tasting guide, quality is judged by nose and palate, not by sight.

Conclusion

From olive harvesting to bottling, every phase of extra virgin olive oil production is an opportunity to do well or to lose quality. Harvesting timing, fruit integrity, processing speed, malaxation temperature, extraction system, storage conditions: these are all variables that a producer with a complete supply chain can directly control.

In the next article, we will address a comparison many wonder about but few truly explain: supermarket oil versus artisan extra virgin olive oil. Industrial chain vs. short supply chain, olive quality, processing times, taste, and preservation — everything you need to know to make an informed choice.

Oleificio Paolo Demuru — Ilbono, Ogliastra, Sardinia.
Complete supply chain: from our olive groves to your table.