One sentence explains the whole olive harvest. The University of California's extension service puts it like this: while olives are on the tree, the oil inside the fruit is in perfect condition — low acidity, true to the variety in flavour, not oxidised. «Changes that influence quality occur during and after harvest.»

Which means the harvest is not the beginning of quality but the start of its loss. What happens at that moment, and in the hours after it, decides whether the oil in the flesh becomes an extra virgin olive oil or a bottle that will eventually have to be refined. This article shows how the right moment is determined, how olives are picked, and why the clock matters more than the machine.

The crop year begins on 1 October

The olive oil world does not count in calendar years. The International Olive Council defines the olive crop year for olive oil as the «period from 1 October of year n to 30 September of year n+1»; for table olives it runs from 1 September to 30 August. When the trade talks about the «2026/27 campaign» in autumn, that is the period meant.

For a Swiss buyer one label claim follows directly from this: the harvest year. The ordinance on foodstuffs of plant origin, mushrooms and table salt (VLpH, SR 817.022.17) permits it in Article 12 paragraph 4 only where 100 per cent of the contents of the pack come from that harvest. A harvest year is therefore the hardest freshness claim a label can carry — and the direct link between what happens on the tree in this article and what stands on the shelf.

When is the right moment? The maturity index

The Olive Council has published a method for this question, guide COI/OH/Doc. No 1 on determining the characteristics of oil-olives. It starts with what you can see: «The skin usually turns from deep green to violet and black. The colour and texture of the flesh also change during these stages as do the colour and sensory characteristics of the oil.» This colour change is known as veraison.

From that a number is derived. The maturity index, developed at the Venta del Llano experimental station of IFAPA in Mengíbar (Jaén), sorts a sample into eight colour categories from 0 to 7: category 0 is deep green skin, category 2 green with reddish spots on less than half the fruit surface («start of colour change»), category 4 black skin with white flesh, category 7 black skin with the flesh purple all the way to the stone. The distribution across these classes gives the index.

In practice, according to the Council, it takes «at least four rounds of sampling» to reach a reliable conclusion; sampling should start «about one month before harvest traditionally begins» and be repeated at intervals of seven to ten days. The optimum point is reached when the aroma is intensely fruity — fresh green olives, other green fruit, freshly mown grass, artichoke — the taste freshly fruity with a balance between bitterness, pungency and astringency, the extraction capacity above 70 per cent and the free acidity between 0.1 and 0.3 per cent. The Council notes: «Normally almost all the varieties have a maturity index between 3 and 4 at this point, making it advisable to start harvesting in order to obtain distinctive premium oils.»

There is a second, cruder signal: the force with which the fruit holds to its stalk. Values below 3 newtons are usually a sign of imminent fruit drop, and once more than 5 to 10 per cent of the olives have fallen, the effect on the obtainable quantity of oil is significant. The advice is to start early enough to finish before that threshold.

Why growers pick early – and what picking late costs

Oil formation in the fruit begins forty days after fruit set, is intense between day 60 and day 120, and slows afterwards; beyond 120 days from full bloom, senescence sets in. The decision falls inside that window.

The Council's key sentence on the subject is this: «If the olive fruits are healthy, the level of free acidity and the peroxide value of the oil do not change during ripening. In contrast, the polyphenol content, organoleptic characteristics and colour can vary.» A healthy olive will therefore still give a chemically sound oil late in the season. What it no longer gives is the polyphenols — and with them the taste and the keeping quality.

The curve is bell-shaped: the content rises in the early ripening phase and falls again afterwards, and the Council names a target above 100 ppm expressed as gallic acid. The sensory profile follows directly: «Bitterness and pungency are characteristics of oils obtained from early-harvested olives.» Tocopherols and sterols also decrease in the advanced stages of ripening, and resistance to oxidation depends essentially on the polyphenols present.

Research confirms the pattern from several directions. A study in Molecules (2020) on two varieties found that «the total phenolic content was decreasing during ripening», and that the decline becomes more intense as ripeness advances. A paper in Antioxidants (2024) describes, for every genotype examined, an intense rise in hydroxytyrosol and tyrosol derivatives just after fruit set followed by a constant decrease; the relationship between the phenolic content of the fruit and that of the oil showed a correlation coefficient of 0.946. And a sensory review in Foods (2026) sums up that bitterness and pungency generally decrease during ripening and that polyphenol biosynthesis is most active in the early stages, peaking around the half-pigmentation point.

The practical arithmetic comes from the University of California: in varieties with a low polyphenol content, starting a month later can cost four months of shelf life — «a one-month delay in harvest can cause a four-month loss in oil stability due to the drop in polyphenol content».

So why does anyone pick late? Because the scales say something else. Later-harvested olives usually yield a higher percentage of oil per tonne of fruit, and that is what counts for the grower. Except that the gain is largely an illusion: «Olives naturally lose moisture in the maturation process. The perceived rise in oil content, late in the growing season, is actually a loss of moisture.» The fruit does not become oilier; it becomes drier. Picking early means paying in volume for polyphenols — that is the whole trade-off, and it explains the price gap on the shelf. What an early harvest tastes like is covered in early-harvest Picual; how much the right moment varies between varieties is in olive varieties in Europe.

How olives are picked

Harvesting is the most expensive operation in the grove. Done traditionally it accounts, according to the Council, for 50 to 80 per cent of production costs — hence the pressure to mechanise.

Physically, the methods differ in the force applied to the fruit. In hand harvesting the olives are detached mainly by traction; beating with poles transmits traction and flexion; machinery that produces vibrations adds torsion, and the vibratory method has proved the most effective. The Council's productivity figures:

  • Hand picking with plastic rakes: 10 to 15 kilograms per hour per worker. Mechanical aids double that, to 20 to 30 kilograms.
  • Mechanical pole beaters: around 40 to 50 kilograms per hour per worker.
  • Trunk shakers with nets: roughly 60 to 80 kilograms per hour per worker. The machines use 30 to 50 kilowatts, a frequency of 15 to 30 hertz and an amplitude of 20 to 30 millimetres; the shaker head weighs 400 to 600 kilograms in total. They are most efficient with wrap-around catching frames.
  • Spreading nets: about 100 kilograms per hour per operator.
  • Straddle harvesters for hedgerow plantings: side-shaking machines borrowed from the vineyard, with the number of shaker bars raised from four to ten or twelve. According to the Council they do an excellent job on small trees of two to three metres in height and 0.8 to 1.2 metres in width; harvesting productivity in the super-intensive grove is very high, and such orchards are expected to last 13 to 15 years.

For quality, the same rule applies to every method, and the University of California states it most concisely: «The key is to not break the fruit skin in any way and to process the fruit within a few hours.» Hand harvest is the best but very expensive; done properly with the right equipment, mechanical harvest can be almost as good and much cheaper. Pole harvesting carries a side cost the Council mentions in its plant-health chapter: the poles cause wounds and so favour the establishment and spread of the bacteria behind olive knot.

And then there is the method that is not one: letting the fruit fall naturally and picking it up off the ground. The verdict is unambiguous — «Ground fruit produces a low quality, low value oil that is refined. In many countries, this oil forms the base for low cost oils.» Even the net method has the drawback, in the Council's words, that overripe olives are collected along with the rest; in the long run the system should be replaced by tree shapes that let the fruit be harvested economically on the tree.

Why ground olives give worse oil is spelled out in the Council's own sensory method. The defect «musty-humid-earthy» is defined there as the characteristic flavour of oils from fruit in which large numbers of fungi and yeasts have developed because it was stored in humid conditions for several days — «or of oil obtained from olives that have been collected with earth or mud on them and which have not been washed». Earth on the olive is not untidiness; it is a named sensory defect. What it and its relatives smell like is in how to tell if olive oil is rancid.

That separating ground fruit from tree fruit is more than advice is shown by the specifications of the protected designations. The Spanish PDO Priego de Córdoba requires the harvest to be carried out «separando suelo y vuelo» — keeping ground and tree apart — and only healthy olives picked directly from the tree to be used for the protected oil. The PDO Sierra de Cazorla requires the same.

From tree to mill: the hours that count

This is the most underestimated part. There is no general statutory maximum between picking and milling — neither in EU marketing law nor in the Council's standards. Where binding deadlines do exist, they sit in the specifications of the protected origins, and they are strict:

  • PDO Olio Extravergine di Oliva del Chianti Classico: the olives must be detached directly from the tree and harvested «prima del 31 dicembre di ogni anno». Any interim storage may only take place in cool, ventilated rooms and «per non più di tre giorni dalla raccolta», in stackable crates perforated on five sides, in layers no deeper than 30 centimetres. Processing must happen «entro le ventiquattro ore dal conferimento nei frantoi», and the temperature of the extraction plant may not exceed 27 °C.
  • PDO Priego de Córdoba: «El plazo máximo para la molturación de la aceituna será de dos días a partir del momento de su recolección» — two days, as a condition for the oil to carry the designation at all.

What happens when those deadlines slip is also named. The defect «fusty/muddy sediment» is defined in the Council's method as the characteristic flavour of oil from olives piled or stored in such conditions as to have undergone an advanced stage of anaerobic fermentation. The heap of olives in the yard is the direct cause of a defect that disqualifies an extra virgin.

The corresponding practice: shallow, ventilated crates instead of deep containers, so the fruit at the bottom is not crushed, and ideally no storage at all. A study in Plants (2023) quantified this: cooling to 5 °C for five days maintained quality, whereas the quality of olives kept at room temperature dropped drastically after five days; assessors found off-flavours in those samples mostly linked to fermentation and oxidation processes.

And here the circle closes back to the picking method. A study in Foods (2026) on the Istrian variety Buža compared three harvesting methods and found that the method did not significantly affect total phenolic content and that free fatty acids stayed low in all three cases — «despite differences in the extent and type of fruit damage» — which the authors attribute to prompt processing within 24 hours. What was measurable was mainly a slight reduction in green odour attributes with the hand-held vibrator compared with hand picking. Put differently: mechanical damage to the fruit only turns into a defect once time and warmth are added.

The calendar, country by country

The northern hemisphere campaign runs through autumn and winter, but it has shifted. The Junta de Andalucía notes in its official crop estimate that recent seasons show the start of picking moving earlier, beginning in October and with more of the crop gathered in November and December, at the expense of the final months of the campaign.

How large that shift is, the Priego de Córdoba specification documents in its own text: traditionally the harvest began the day after 8 December and lasted until March or April. «Sin embargo, en los últimos años, y sobre todo desde la creación de la Denominación de Origen, la recolección se inicia en el mes de Noviembre, dando así lugar a la obtención de aceites de mayor calidad.» A legal document that explicitly attributes higher quality to moving the harvest a month earlier — the central claim of this article does not get stated more plainly than that.

In Tuscany, the Chianti Classico specification sets the line at 31 December. For Greece, a report by the US Department of Agriculture gives the period October to January, depending on autumn rainfall, with a possible extension into February.

And in Switzerland?

There is a Swiss olive harvest, small though it is. The inventory of Switzerland's culinary heritage describes Ticino olive oil: in October and November, when the olives are at the stage of turning from green to blackish violet, they are picked, shaken from the branches by hand or machine, caught in nets and taken to the mill.

That is exactly the ripeness the Olive Council describes as optimal, and exactly the net method it recommends. The volumes are modest: in 2020 the two Ticino mills in Sonvico and Losone produced, according to the same source, around 2,000 litres of olive oil. More on Swiss growing is in olive oil from Switzerland.

Frequently asked questions

When are olives harvested?

In the northern hemisphere, in autumn and winter. The crop year for olive oil runs, according to the International Olive Council, from 1 October to 30 September. In Andalusia picking now begins in October with the bulk in November and December; in Tuscany it must be finished before 31 December for the Chianti Classico PDO; in Greece it runs from October to January. In Ticino, picking takes place in October and November.

Is early-harvest olive oil better?

For taste and keeping quality, yes. The Olive Council records that bitterness and pungency are characteristics of oils from early-harvested olives and that the polyphenol content falls again after an early peak. Resistance to oxidation depends essentially on those polyphenols. In low-polyphenol varieties, a month's delay can cost four months of shelf life, according to the University of California.

Don't riper olives yield more oil?

Apparently yes, in truth only partly. The higher percentage of oil per tonne of fruit at the end of the campaign is, according to the University of California, essentially a loss of water: the olive dries out, so the percentage of oil rises. That is why late picking happens, even though it is sensorially worse.

Why do olives picked off the ground make poor oil?

Because earth and moisture encourage fungi and yeasts. The Olive Council's assessment method defines the defect «musty-humid-earthy» expressly to include oil from olives collected with earth or mud on them that have not been washed. Fruit gathered from the ground gives, in the University of California's words, a low-quality oil that has to be refined.

How quickly must olives reach the mill?

There is no general legal deadline. The specifications of protected origins set their own: Chianti Classico requires processing within 24 hours of delivery and allows at most three days of interim storage in cool, ventilated rooms; Priego de Córdoba sets two days from picking. Where olives are piled up, the sensory defect «fusty/muddy sediment» arises through anaerobic fermentation.

Does the harvesting method matter for quality?

Less than you might think, provided milling follows promptly. A study on the variety Buža found no significant effect of the harvesting method on total phenolic content and low free fatty acids with all three methods, despite differing fruit damage — attributed to processing within 24 hours. What stood out was mainly a slight decrease in green odour attributes with the hand-held vibrator. What remains decisive is not breaking the fruit skin and processing quickly.

Sources

Note: This article is for general information only and does not replace advice from a doctor or dietitian. If you have health questions, please consult a professional.