Olive oil is made by crushing whole olives into a paste, slowly mixing the paste so the oil droplets join up, then spinning it in a centrifuge to separate the oil from the water and solids. That mechanical process gives extra virgin and virgin olive oil. Refined olive oil is different: defective oil is neutralised, bleached and deodorised with heat to make it edible, which also strips out its flavour and polyphenols. It typically takes about 5 to 6 kg of olives to make a litre of oil.
How is extra virgin olive oil made, step by step?
- Harvest. Olives are picked by hand, with poles and nets, or by tree shakers. For high-quality oil the fruit should reach the mill within hours, because bruised olives start to ferment and oxidise. Early-harvest oil comes from green olives picked in autumn; see early harvest olive oil.
- Cleaning. Leaves, twigs and dust are blown off and the olives are washed.
- Crushing. Whole olives, pits included, are ground into a paste, usually in a hammer or disc mill. Traditional mills used granite stones.
- Malaxation. The paste is stirred slowly, typically for 20 to 45 minutes, so small oil droplets merge into larger ones. Time and temperature here shape the oil: warmer and longer gives more oil but loses aroma and polyphenols. For "cold extraction" the paste must stay below 27 °C.
- Separation. A horizontal centrifuge (decanter) spins the paste and separates oil from water and solids. Older mills pressed the paste on mats in a hydraulic press, which is where "first cold pressing" comes from.
- Clarifying. A second, vertical centrifuge removes remaining water. The oil may then be left to settle or be filtered. Unfiltered oil is cloudy and keeps for less time; see filtered vs unfiltered olive oil.
- Storage and bottling. Good producers store oil cool, in stainless steel, often under inert gas, and bottle it in dark glass or tin to slow oxidation.
Whether the result is extra virgin is decided afterwards, by laboratory chemistry and a tasting panel. Our guide to what extra virgin olive oil is lists the grades.
What is refined olive oil, and how is it made?
Refined olive oil starts as lampante oil, virgin oil too defective to eat as it is (the name comes from its old use as lamp oil). Refining removes the defects, and almost everything else:
- Neutralising with an alkali removes free fatty acids, which brings acidity down to 0.3% or less.
- Bleaching with clay or activated carbon removes colour and some contaminants.
- Deodorising with steam at high temperature under vacuum strips out off-odours, along with the fresh aromas.
- Winterising may remove waxes so the oil stays clear when cold.
The result is a pale, almost tasteless oil with very few polyphenols. On its own it is sold to industry. Blended with a share of virgin oil for colour and flavour, it becomes the bottle labelled simply "olive oil", "pure olive oil" or "light olive oil".
Olive pomace oil goes one step further. After the first extraction, the leftover paste (pomace) still holds some oil, which is extracted with a solvent such as hexane, then refined and blended. It must be labelled as pomace oil, never as olive oil.
How much olive oil do you get from olives?
Olives are roughly 15 to 25% oil by weight, depending on variety and ripeness, and mills recover most of it. That works out to about 5 to 6 kg of olives for a litre of oil. Green, early-harvest olives hold less oil, so they can need considerably more fruit per litre, which is one reason high-phenolic oil costs more.
Where do polyphenols go during processing?
Most of the olive's phenolic compounds are water-soluble, so much of them leaves with the water during separation. What stays in the oil depends on the fruit, a short and cool malaxation, and how little oxygen the oil sees afterwards. Refining removes most of what remains. That is why only extra virgin and virgin oils carry meaningful polyphenols, and why fresh, carefully milled oils carry the most. See polyphenol levels in olive oil.
How Pomoni's oil is made
Pomoni's oil is early-harvest Koroneiki from a single Greek grove, picked green and milled within hours by cold extraction, then stored and shipped in dark glass. Each harvest is tested by HPLC; the certificates are on our testing page. More on the mill itself is in inside Pomoni's milling process.
Frequently asked questions
Is olive oil pressed or spun?
Today almost all olive oil is separated in a centrifuge. Traditional hydraulic presses still exist, but they are a small share of production.
Is refined olive oil bad for you?
It is safe to eat and has the same fat profile as other olive oils, but refining removes most of the polyphenols and flavour that set extra virgin oil apart.
Is olive oil made with chemicals?
Extra virgin and virgin olive oil are made by mechanical means only, with no chemicals. Refined olive oil and pomace oil are processed with chemicals and heat.
How many olives does it take to make a litre of olive oil?
Usually about 5 to 6 kg, and more for green, early-harvest olives, which hold less oil.
Sources
- Commission Delegated Regulation (EU) 2022/2104 on marketing standards for olive oil (categories and "cold extraction" / "first cold pressing" terms). eur-lex.europa.eu
- International Olive Council. Trade standard COI/T.15/NC No 3/Rev. 22 (olive oil categories), 2026. internationaloliveoil.org
