Extra virgin is not a date on the calendar: it is a number. Four, in fact

«This is extra virgin» is not a judgement: it is a commercial category, and like every category it has written boundaries. An oil is extra virgin if it sits simultaneously inside four limits — two chemical, one spectrophotometric and one sensory — set by Regulation (EEC) 2568/91 and by Annex VII of Reg. (EU) 1308/2013. Overstep just one and the oil drops a category, however good it tastes to you.

The interesting part is another one: all four of those numbers are decided before the olives reach the mill. The miller can ruin a good batch, but cannot rescue one that arrives in bad shape. What follows is what the research says about when to harvest, and why the window is narrower than people think.

The first number: 0.8, and it is not the taste

Free acidity cannot be tasted: it is the share of fatty acids that have broken away from the triglycerides, measured in grams of oleic acid per 100 g of oil. What breaks them away are the lipases, enzymes that kick in when the fruit is wounded, attacked by the fly, bruised or simply left waiting.

From this follows a practical fact that surprises many: a healthy olive picked up off the ground can give an oil outside the category, while the same olive taken from the tree and milled the same day stays well below 0.8. It is not a question of variety or of mill: it is a question of how much time and how much damage there was between tree and milling.

The second: 20 meq O₂/kg, that is, how much oxygen it has already eaten

The peroxide value measures oxidation that has already happened: how many peroxides have formed through the reaction between unsaturated fats and oxygen. It rises with heat, with light, with contact with air — while the olives wait, during milling, and then while the oil is stored.

K232 and K270 are the same story read another way: two absorbances in the ultraviolet that reveal oxidation products a taster's nose cannot yet detect. They exist to catch in the laboratory what still seems fine at first taste.

The fourth number is a human being

The panel test is the only parameter decided by people: a group of trained tasters scores the defects (fusty, winey, musty, muddy sediment, rancid) and the fruitiness. For an oil to be extra virgin the median of the defects must be zero and the median of the fruitiness greater than zero. A single perceived defect, and the oil becomes «virgin»; if the defect is marked, it becomes lampante and is not even edible without refining.

It is the parameter that punishes haste and delay most harshly: the commonest defects are not born on the tree, they are born in the heap of olives left two days in a sack.

When to harvest: the scale the technicians use

«When they have turned colour» is a good rule in the field, but there is a way of saying it with a number: the Jaén maturity index, born in the Seventies at the Andalusian olive-growing station and today used all around the Mediterranean. You take a representative sample, count 100 olives, assign each one a class from 0 to 7 based on the colour of skin and pulp, multiply each class by the number of fruits belonging to it and divide by one hundred.

The classic reference for quality oil lies between 2 and 4, with 3-3.5 as the most quoted value. But «optimal» depends on what you want: the literature shows that the best index changes with the cultivar and with the goal — on Chemlal, for instance, a study in Food Chemistry identifies as the best moment an index of around 2.4 for oils of high chemical quality. Those aiming at yield wait; those aiming at polyphenols move earlier.

Polyphenols: the capital you spend by waiting

The phenolic compounds — oleuropein, hydroxytyrosol, tyrosol, oleocanthal, oleacein — do three things at once: they give the bitterness and the pungency, they protect the oil from oxidation and lengthen its life, and they are the ones to which the European Union recognises a health effect.

Their course in the fruit is not linear: they rise to a peak that falls in the early stages of colour change, then decline as ripening proceeds. Harvest late and you get more oil, but an oil with fewer defences and less character.

That horizontal line is the most concrete thing in the whole article. Regulation (EU) 432/2012 authorises on the label the wording «olive oil polyphenols contribute to the protection of blood lipids from oxidative stress» only if the oil contains at least 5 mg of hydroxytyrosol and derivatives per 20 g of oil — that is, doing the arithmetic, 250 mg/kg. It is the only health claim recognised for olive oil, and it applies only to virgin and extra virgin, because refining takes those compounds away.

An oil harvested at advanced ripeness can be perfectly extra virgin and still sit below that threshold. Two oils of the same cultivar, from the same grove, harvested three weeks apart, can sit one above and one below.

The hours between tree and mill

Here the research is clear-cut. A CNR-IBE study published in Foods in 2021 followed 228 batches of olives in seven industrial mills across three seasons, comparing four classes of waiting time before milling: within 24 hours, 2-3 days, 4-6 days, 7 days and over.

The result: free acidity, peroxide value and K232 increase in a statistically significant way as the wait lengthens, while the phenolic content decreases. α-tocopherol, lutein and β-carotene fall too. On tasting, fruitiness, green notes, bitterness and pungency are reduced and defects grow. The fatty acid composition, on the other hand, does not change: that is genetics.

Translated into practice: olives do not stockpile. A day's harvest goes to the mill that day or the next morning, in perforated crates that let the air through. The sack is the quickest way to turn a good batch into an oil of a lower category.

The harvesting method weighs as much as the date

The three levers that decide the four numbers are timing, integrity of the fruit and time. The second and the third depend on how you harvest.

• Olives off the ground or from natural drop: already wounded, often fermented, almost always with high acidity. They must be kept separate, not mixed with those taken from the tree.
• Hand harvesting: maximum integrity, very low hourly output. On a real grove it means stretching the harvest by weeks, and the weeks are paid for in polyphenols.
• Mechanical harvesters: the compromise that holds the three levers together — the fruit comes down whole, the harvest day is closed, the batch leaves for the mill.

On this, the only technical caution is the setting: a stroke that is too energetic on young trees takes away leaves and the year's shoots; one that is too gentle on stubborn varieties leaves half the crop on the tree and stretches the timetable. That is why our Falco EVO 42 and the EVO 42 ULTRA version have a three-speed selector: the variety in front of you changes, so the setting must be able to change with it. Which one to use on each cultivar we have written in the guide to Italian olive cultivars.

The window, in one line

If we had to sum up the whole literature in one operating rule: harvest when the maturity index is between 2 and 4, with the fruit intact, and take the olives to the mill within 24 hours. Inside that window you get an oil that has the numbers to be extra virgin, the polyphenols to stay good for a year and the fruitiness a panel recognises.

Outside that window you can still make an extra virgin — but you are playing with less margin, and the margin is eaten by the fly, by a day of rain or by a mill that is full. If you have not yet prepared the grove and the equipment, the checklist for the three weeks before is the step that comes before this one.

Sources

• Reg. (EEC) 2568/91 and subsequent amendments — methods of analysis and category limits; Reg. (EU) 1308/2013, Annex VII.
• Reg. (EU) 432/2012 — list of authorised health claims: olive oil polyphenols, threshold of 5 mg per 20 g.
• Rotondi A., Morrone L., Bertazza G., Neri L., Effect of Duration of Olive Storage on Chemical and Sensory Quality of Extra Virgin Olive Oils, Foods 10(10), 2296, 2021 — CNR-IBE, 228 batches, 7 mills, 3 seasons.
• Influence of time of harvest and maturity index on olive oil yield and quality, Scientia Horticulturae — effect of harvest timing on yield and quality.
• Influence of olive ripeness on chemical properties and phenolic composition of Chemlal extra-virgin olive oil, Food Chemistry — optimal maturity index around 2.4.
• Assessing Optimal Olive Harvesting Time: A Comparison Between Visual Ripeness, Maturity Index, and Pulp Hardness, Agriculture 2026.

If you want an opinion on setting up the tool for your variety, call us: +39 0865 860247, a technician who has seen those trees will answer.