How is olive oil made?

1. Olives grow on trees in sunny groves. At harvest the branches are shaken and the olives fall into nets. Each olive holds tiny drops of oil in its soft flesh.
2. At the mill a strong fan blows away the leaves and twigs, which are much lighter than olives. Then the olives are washed to rinse off the dust and soil.
3. Heavy wheels or spinning hammers crush the whole olives, pits and all, into a thick paste. Crushing breaks the olives open so the oil can get out.
4. The paste is stirred slowly for about half an hour. The tiny drops of oil bump into each other and join into bigger drops, which are much easier to collect.
5. Then the paste is spun very fast. Spinning pushes the heavy bits of skin and pit to the outside, then the water. The oil is lightest, so it ends up apart from the rest.
6. Out flows golden-green olive oil. It is kept in dark bottles or steel tanks, because light, heat and air slowly spoil its taste.

This machine is cut open so you can see inside. Tap each part to see what it does.

• Feed pipe. Olive paste from the mixer is pumped in through this pipe, right into the middle of the spinning drum.
• Spinning drum. The drum spins thousands of times every minute. Everything inside is pushed hard against its wall, heaviest things first.
• Screw. A giant screw turns inside the drum, just a little slower than the drum itself. It scrapes the solid bits along the wall toward the narrow end.
• Solids. The crushed skin, flesh and pits are the heaviest part, so they pack against the wall. They come out here as a damp crumble called pomace.
• Olive water. Olives hold water as well as oil. The water is heavier than oil, so it makes the middle layer and leaves through its own outlet.
• Olive oil. Oil is the lightest part, so it stays nearest the middle of the spin and flows out here, golden-green and fresh.

Spin a tube of paste straight away. Then stir the paste slowly for a while and spin again. Compare the tubes on the rack.

Experiment: What does slow stirring do before the paste is spun?

1. Press Spin without stirring. Look at how thick the golden layer is.
2. Tap the mixer until it shows 20 minutes or more. Watch the drops in the magnifying glass.
3. Spin again and compare the two tubes on the rack.

What we found: Stirring first gives a much thicker layer of oil. In fresh paste the oil is in drops so tiny that they stay mixed in. Slow stirring lets them join into big drops, and big drops separate easily when the tube is spun.

Turn on JavaScript to try it yourself.

Get at least 15 liters of oil from the batch. Mix, choose the spin speed, spin, then tap the oil layer to bottle it.

An olive is a small fruit with a hard pit. Its soft flesh is full of tiny drops of oil, far too small to see, mixed in with water. To get the oil, you have to break the olive open and then sort the oil from everything else. Nothing needs to be added: olive oil is made just by crushing, stirring and separating.

Crushing turns the olives into a thick paste. Now the oil is out of the fruit, but it is still in very tiny drops, spread all through the paste. Tiny drops do not separate well. So the paste is stirred slowly for about half an hour. As it turns over, the tiny drops bump into each other and join up, like raindrops running together on a window.

Then comes the separating. Oil is lighter than water, which is why it floats on top of a puddle or a bowl of soup. The bits of skin and pit are heavier than water. If you left the paste in a jar, it would slowly settle into three layers: solids at the bottom, water in the middle and oil on top. That takes hours.

A spinning machine does the same job in seconds. Spinning pushes everything outward, and the heaviest things are pushed hardest. The salad dressing comparison is good for the layers, but not perfect: dressing only has to separate oil from water, while olive paste has solid bits to remove as well.

Key words

Olive paste

The thick mash made by crushing whole olives, pits and all.

Malaxation

Slowly stirring olive paste so tiny drops of oil join into bigger ones.

Density

How heavy something is for its size. Oil is less dense than water, so it floats.

Centrifuge

A machine that spins things very fast to separate heavy parts from light parts.

Pomace

The solid leftovers: bits of skin, flesh and pit.

Coalesce

When small drops merge into bigger drops.

Check your thinking

1. Where is the oil before the olives are crushed?

   Show the answer

   In tiny drops inside the olive's flesh. The soft flesh of the olive is full of tiny oil drops. Crushing lets them out.

2. A jar of oil, water and sand is shaken and left to stand. What order do the layers settle in, from top to bottom?

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   Oil, water, sand. The lightest goes on top and the heaviest sinks. Oil is lighter than water, and sand is heavier.

3. Why is the olive paste stirred slowly before it is spun?

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   So tiny drops of oil can join into big drops. Big drops separate easily. Tiny drops stay stuck in the paste.

4. Why does a mill spin the paste instead of leaving it to settle in a tank?

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   Spinning separates it in seconds instead of hours. Spinning pushes outward much harder than gravity pulls down, so the layers form very quickly.

5. A miller warms the paste to 35 degrees Celsius to get more oil. What is the trade-off?

   Show the answer

   A little more oil, but delicate flavors are lost and the oil spoils sooner. Warm oil flows and coalesces more easily, which raises yield slightly, but aroma compounds escape and oxidation speeds up. That is why quality oil is kept below about 27 degrees.

6. Why is olive oil kept in dark bottles?

   Show the answer

   Light slowly spoils its taste. Light, heat and air slowly change the oil and make it taste stale.