How Olive Oil is Made

Olive oil has been pressed from fruit for thousands of years — but the way we make it has changed dramatically. From ancient stone mills and hanging-rock presses to hydraulic systems and modern centrifuges, each era brought new tools and new quality. Here's the full story.

The Short Answer

Olive oil is made by crushing olives into a paste and then separating the oil from the water and solids. Simple in concept — but the tools used to do it have evolved over thousands of years, and those changes have everything to do with why great olive oil today is better than it's ever been.

The Ancient World: Stone Mills and Lever Presses

Ancient stone mill and lever press used to make olive oil

The earliest olive oil was made with stone and leverage. Olives were first crushed under large circular millstones — heavy wheels rolled over the fruit to break the flesh and release the oil. The resulting paste was spread onto woven fiber mats, stacked in layers, and placed under a press.

That press was a feat of ancient engineering: a massive wooden beam — sometimes 40 to 50 feet long — was anchored at one end into a thick stone wall. Heavy rocks were hung from the free end, or the beam was twisted down with ropes and a windlass. The weight and leverage of the system squeezed the olive paste through the mats, and the oil ran down into collection basins below.

This lever-and-weight press was the dominant technology across ancient Greece, Rome, and the broader Mediterranean world for centuries. It worked. But it was slow, labor-intensive, and exposed the oil to prolonged contact with air, heat, and the olive's own enzymes — all enemies of quality.

The Industrial Era: Hydraulic Presses

Industrial hydraulic press used for olive oil production in the 19th and 20th centuries

The invention of the hydraulic press in the late 18th century transformed olive oil production. Instead of relying on hanging rocks and long wooden beams, hydraulic systems could apply enormous, consistent pressure with far less physical effort. Mills could process more olives, more quickly, and with greater control over the amount of force applied.

Hydraulic presses became the industry standard through much of the 19th and 20th centuries. The basic process remained similar — crush the olives, press the paste — but the scale and efficiency improved dramatically. Still, the batch nature of pressing meant olives sat in contact with air and their own enzymes for extended periods, which could degrade flavor and increase acidity.

The Modern Revolution: Continuous Centrifuge Production

Modern continuous centrifuge olive oil mill production line illustration

The real leap in olive oil quality came with the widespread adoption of the continuous centrifuge system in the latter half of the 20th century. This technology changed everything.

Here's how it works:

  • Olives are crushed into a paste via an enclosed "hammer mill"
  • The paste is gently malaxed (slowly churned), at a precise temperature to help oil droplets coalesce
  • The paste is fed continuously into a horizontal centrifuge (called a decanter) that spins at high speed, separating oil from water and solids by density
  • A second vertical centrifuge, spinning at a very high speed, polishes the oil, removing any remaining moisture or fine particles

The key word is continuous. Unlike batch pressing, the entire process is enclosed. The olives and oil move through the system quickly, and the oil is separated almost immediately.

Why Continuous Production Means Better Oil

Three factors above all others determine olive oil quality: oxygen exposure, temperature, and time. The continuous centrifuge system controls all three.

Limiting Oxygen

Oxidation is the primary enemy of olive oil quality. It degrades flavor, destroys phenolics, and shortens shelf life. The closed, continuous centrifuge system dramatically limits the oil's contact with air throughout the entire milling process — something that was simply impossible with open stone mills and mat presses.

Controlling Temperature

Heat destroys the delicate aromatic compounds and phenolics that make great olive oil great. Modern mills carefully monitor and control temperature throughout the process. True cold-pressed or cold-extracted oil never exceeds 27°C (80°F), preserving the fresh, grassy, peppery flavors that define high-quality extra virgin olive oil.

This is why you'll see "cold pressed" or "cold extracted" on quality labels — it's not marketing language. It's a meaningful production standard.

Speed

With continuous production, olives can go from harvest to bottled oil in a matter of hours. This matters enormously. The moment an olive is picked, its quality begins to decline. The faster it's milled, the better the oil.

What This Means for Quality

The shift to continuous centrifuge production is one of the primary reasons that high-quality extra virgin olive oil today is genuinely superior to what was available even a few decades ago. Lower acidity, higher phenolic content, more vibrant flavor, and longer shelf life are all direct results of better milling technology — combined with careful harvesting practices.

It's also worth noting that not all mills use the same standards. A centrifuge system run carelessly — at high temperatures, with long malaxation times, or with olives that sat too long before milling — can still produce mediocre oil. The technology enables quality. It doesn't guarantee it.

The Sciabica Approach

We've been milling California olives for generations. We harvest early to capture peak phenolic content, mill quickly to preserve freshness, and bottle with care to protect what we've worked so hard to produce.

The technology has evolved from stone to steel — but the commitment to honest, high-quality oil is the same as it's always been. That's what sunshine in a bottle really means.