How Olive Oil Is Made.
Traditional vs Modern Extraction Methods

How olive oil is made, the journey from crushing olives to bottling the finished product is far more complex than most consumers realise. The extraction method chosen at the mill determines the polyphenol content, sensory profile, oxidative stability, and health benefits of the final oil. Understanding the differences between traditional stone-milling and cold-pressing methods versus modern centrifugation-based cold extraction helps readers appreciate why Greek extra virgin olive oil produced with precision technology often delivers superior quality to oils made with older, romanticised methods.

This article explores the science behind olive oil extraction methods, contrasts traditional and modern techniques, and explains how each choice impacts the polyphenols, early-harvest complexity, and overall quality that define premium extra virgin oils.

The Complete Olive Oil Extraction Journey

Before examining specific extraction methods, it’s important to understand the full journey of how olive oil is made from harvest to bottle.

Step 1: Harvest and Transport

The harvest method, hand-picking or mechanical shaking, and speed of transport to the mill are the first critical variables. Olives begin to oxidise and ferment immediately after leaving the tree. Producers aiming for high-polyphenol, early-harvest oils must deliver fruit to the mill within hours (ideally under 6 hours) to preserve volatile aromatic compounds and phenolic content.

Green olives harvested early contain higher levels of oleocanthal, hydroxytyrosol, and oleuropein aglycon, the bioactive compounds that create the peppery sensation and provide the strongest health benefits. Late-harvest, fully ripe olives have lower polyphenol levels and milder flavour profiles.

Step 2: Washing and Sorting

Olives arrive at the mill coated in leaves, soil, and debris. Washing removes these contaminants; sorting removes unripe, over-ripe, or damaged fruit that would compromise oil quality or introduce off-flavours.

Step 3: Crushing (Grinding) into Paste

This is where extraction methods begin to diverge significantly. The crushing process breaks down olive cell walls and releases the oil droplets held inside. Two primary crushing technologies exist:

• Stone mills (molazze): Traditional cylindrical stones rotating over a granite base. They crush olives gently, creating larger oil droplets and releasing less chlorophyll, but process olives more slowly.
• Hammer mills and metal crushers: Modern stainless steel equipment that rapidly crushes olives into a fine paste. Faster processing but can generate more heat through friction if not carefully controlled.

For cold extraction methods aiming to preserve polyphenols, crushing must keep paste temperature below 27°C, a threshold that separates “cold” from warm-temperature processing.

Step 4: Malaxation (Mixing)

After crushing, the olive paste is slowly mixed in a process called malaxation. This gentle stirring helps microscopic oil droplets merge into larger ones, improving separation efficiency. Malaxation typically lasts 15–45 minutes and must stay below 27°C to protect aromatic compounds and polyphenols from heat degradation.

Longer malaxation times increase oil yield but reduce aroma complexity and phenolic content, a trade-off between quantity and quality that premium producers resolve in favour of quality.

Step 5: Extraction (Separation of Oil from Solids)

This is where traditional vs. modern methods diverge most dramatically, fundamentally affecting the final oil’s composition.

Traditional Extraction: Stone Mills and Cold Pressing

The Historical Method

For centuries, olive oil was extracted using mechanical pressure. The malaxed paste was spread onto fibre mats or woven esparto discs, stacked, and pressed using:

• Lever systems weighted with stones
• Screw-based presses
• Hydraulic presses (invented in the 1830s by agronomist Pietro Ravanas)

Pressure forced oil and vegetation water through the fibre layers, which were then left to settle, allowing oil and water to separate naturally due to their different densities.

Advantages of Traditional Pressing

• Minimal equipment cost: Simple, robust machinery affordable for small producers
• Romantic marketing appeal: “Cold pressed” and “first press” terminology resonates with consumers seeking “natural” methods
• Some polyphenol preservation: When executed correctly at low temperatures, traditional pressing does retain polyphenols

Critical Disadvantages of Traditional Pressing

Research consistently shows that traditional pressing has significant limitations:

• Inconsistent quality and higher defect rates: Long contact between paste and air during pressing allows oxidation, and inadequate hygiene can introduce rancidity or off-flavours
• Lower polyphenol retention: Studies reveal that traditional methods, especially if malaxation extends beyond 45 minutes or temperature control is poor, lose 20–40% of polyphenols compared to modern extraction
• Lower extraction yield: Hydraulic pressing cannot extract all oil, historically leading producers to add hot water for a “second press”, a practice that further degrades oil quality
• Slower processing: Batch-based pressing processes one load at a time, limiting throughput
• Higher water contamination risk: Fibre mats and esparto discs are difficult to clean between batches, risking residual moisture and microbial contamination

Importantly, research by food scientists shows that Cretan oils produced using traditional stone milling, cold pressing, and no centrifugation had approximately 60% higher polyphenol content than many commercial Spanish, Italian, and Greek extra virgins, but this was due to the cultivar and early harvest timing, not the pressing method itself. When polyphenol content is controlled for harvest stage and variety, modern centrifugation methods preserve polyphenols better than traditional pressing.

Modern Cold Extraction: Centrifugation and Superior Science

How Modern Centrifugal Extraction Works

Modern mills employ continuous centrifugation systems that dramatically improve on traditional pressing. The process unfolds in controlled, sequential phases:

1. Crushing: Olives are rapidly crushed into fine paste (temperature controlled below 27°C via water-cooling systems if needed)
2. Malaxation: Paste is gently stirred for 15–45 minutes, still at controlled temperature
3. Horizontal centrifugation: The paste enters a decanter centrifuge, which spins at high speed. Centrifugal force separates oil, vegetation water, and solid pomace based on their different densities. This happens in seconds, not hours, vastly reducing air exposure
4. Vertical centrifugation: The liquid from the first centrifuge (oil + water mixture) enters a vertical centrifuge to separate remaining water and fine solids
5. Optional filtration: Fine filtration may remove remaining micro-particles, improving clarity and stability without significantly affecting polyphenols

The Two-Phase vs. Three-Phase Debate

Historically, mills used three-phase decanters, which added warm water to the paste to aid separation. This water addition diluted polyphenols into the aqueous phase, reducing phenolic content in the final oil by 15–25%.

Two-phase decanters (the modern standard for quality-focused mills) eliminate the water addition step, directly reducing polyphenol loss. Studies confirm that two-phase systems preserve significantly more phenolic compounds than three-phase systems.

Why Modern Centrifugation Is Superior

Scientific evidence increasingly supports modern extraction:

1. Better polyphenol preservation: Rapid, sealed centrifugation minimises oxidation and air contact. Controlled temperature throughout prevents heat damage to volatile aromatic compounds and phenolic molecules
2. Superior hygiene: Stainless steel equipment is easily sanitised between batches, reducing contamination risk
3. Higher and more consistent yields: Centrifugal force extracts more oil than pressing, and continuous processing allows consistent quality control batch to batch
4. Preservation of subtle flavours and aromas: By reducing malaxation time and air exposure, modern mills retain the delicate green-fruit, herbaceous, and peppery notes that define premium early-harvest oils
5. Better control of extraction temperature: Modern mills can cool the paste in real-time, ensuring processing stays below 27°C even in hot climates

A comprehensive peer-reviewed study on Cretan extra virgin olive oils directly compared traditional stone-mill pressing with modern centrifugation (both using early-harvest olives). The conclusion was obvious: traditional production methods (stone milling, cold pressing, no centrifugation) yielded higher antioxidant capacity and polyphenol content, but only when those traditional methods were paired with excellent cultivar, very early harvest timing, and organic, stress-free farming. When comparing oils from the same harvest stage and variety, the centrifuged oils equalled or exceeded the traditionally pressed oils in polyphenol retention.

How Extraction Method Impacts Early Harvest and Polyphenol Oils

Understanding extraction methods is essential for readers interested in high-polyphenol and early-harvest oils, two of Olea Legacy’s core topics.

Temperature Control Below 27°C

Both traditional and modern methods can be “cold,” meaning malaxation and extraction occur below 27°C. However, modern centrifugation offers better temperature control:

• Traditional pressing in summer, in a hot climate, may struggle to keep paste below 27°C if the mill lacks cooling infrastructure
• Modern centrifuges can actively chill paste via water-cooling systems, ensuring precise temperature regulation even in extreme heat
• Maintaining below 27°C protects the oleocanthal and other secoiridoid compounds that deliver the peppery throat-catch and anti-inflammatory benefits

Speed of Processing and Air Exposure

Early-harvest olives are packed with volatile aromatic compounds (geranium, grass, green leaf, herbaceous notes) that oxidise rapidly on exposure to air. Modern centrifugation’s speed is a major advantage:

• Traditional pressing: 2–4 hours from malaxation to oil separation, with the paste exposed to air the entire time
• Modern centrifugation: Oil is separated within minutes of malaxation, reducing oxidative losses

For Greek extra virgin oils where complexity and peppery bite are prised, the speed of centrifugal extraction is a genuine advantage, not a drawback.

Phenolic Compound Preservation

Early-harvest olives contain a wide spectrum of phenolic compounds:

• Secoiridoids (oleocanthal, oleacein): Heat and oxygen sensitive; require rapid, cool extraction
• Simple phenols (hydroxytyrosol, tyrosol): Somewhat more stable but still benefit from minimal air exposure
• Lignans: The most stable; less affected by extraction method

Research shows that rapid centrifugal extraction, especially when paired with two-phase (no added water) technology, preserves secoiridoids better than traditional pressing because it minimises oxidation time.

The “First Cold Pressed” Marketing Myth

The term “first cold pressed” appears on many bottles and carries romantic connotations of ancient tradition and purity. However, this terminology is now outdated and misleading for several reasons:

1. Obsolete terminology: The “first press” vs. “second press” distinction arose from hydraulic pressing days, when hot water was added to pomace for a second extraction. Modern mills don’t do this, making the term anachronistic
2. Often used deceptively: Some producers use “first cold pressed” to imply superiority over modern methods, even though modern centrifugation is scientifically superior
3. No official meaning: There is no regulatory definition of “first cold pressed” in EU, IOC, or USDA standards for olive oil grading. It is purely marketing language
4. Can mask mediocre oil: A traditionally pressed oil from late-harvest, ripe olives can legitimately be called “first cold pressed” whilst delivering inferior polyphenol content compared to a centrifuged early-harvest oil

For consumers: focus on harvest date, early harvest designation, lab-tested polyphenol content, and producer reputation, not on extraction terminology.

Comparing the Methods: A Direct Contrast

How Extraction Methods Connect to Quality, Early Harvest, and Polyphenols

Understanding how olive oil is made directly connects to the broader knowledge of premium olive oil production and quality.

High-polyphenol oils: Modern centrifugal extraction, paired with early harvest and two-phase separation, delivers the highest polyphenol retention. Rapid, sealed processing minimises oxidation of delicate phenolic compounds like oleocanthal and oleacein.

Early harvest benefits: Rapid, cool centrifugation preserves the volatile aromatic compounds and phenolic complexity that define early-harvest oils. The peppery sensation, herbaceous notes, and bitter finish that characterise premium Greek EVOO depend on extracting green olives before oxidation can degrade them.

Greek EVOO quality: Modern Greek mills increasingly use state-of-the-art centrifugation whilst respecting traditional cultivars like Koroneiki, combining heritage with precision. This combination, ancient olive varieties processed with modern technology, delivers the best of both worlds.

Storage and preservation: Understanding extraction methods helps readers appreciate why proper storage is critical. Oil extracted carefully at low temperature must be protected carefully after bottling to maintain its polyphenol profile and sensory integrity.

Fake olive oil detection: Authentic premium oils (extra virgin) must be mechanically extracted and processed cold. Refined oils use entirely different chemical extraction methods. Understanding extraction helps to spot when an olive oil might be mislabelled as extra virgin.

Discover more about the olive oil:

• Early harvest olive oil: Benefits, taste, and value
• High-polyphenol olive oil: Science-backed benefits
• The history of the olive tree and its cultural significance
• How to store olive oil and preserve freshness
• How to spot fake olive oil: 12 proven checks

Frequently Asked Questions: How Olive Oil Is Made and Extraction Methods

Is traditional “cold pressing” better than modern centrifugation?

Both can produce high-quality oil when executed correctly, but modern centrifugation offers superior control, hygiene, and polyphenol retention. Traditional methods have romantic appeal but rely heavily on operator skill and climate conditions to maintain temperature. Modern mills are more reliable and consistent.

Does “cold pressed” guarantee high polyphenols?

No. “Cold pressed” only means temperature was kept below 27°C during processing, an important criterion, but not the only factor determining polyphenol content. Early harvest timing, olive variety, and soil conditions have equally large impacts. A traditionally pressed oil from late-harvest, ripe olives will have lower polyphenols than a centrifuged early-harvest oil.

What is the “first press” if modern mills don’t do second pressing?

The term dates from the era of hydraulic pressing, when hot water was added to pomace for a second extraction. Modern mills no longer do this, making the distinction meaningless. The term persists in marketing but has no regulatory definition.

Why does centrifugation produce higher yields?

Centrifugal force is more efficient at separating oil from water and solids than gravity and manual pressing. Hydraulic presses cannot extract all oil; centrifuges recover more, which is why they became the industry standard.

Does rapid extraction harm olive oil quality?

No. Rapid extraction actually protects quality by minimising air exposure and oxidation. The slower traditional pressing method is more risky for oxidative degradation of volatile compounds.

Can traditional mills produce early-harvest, high-polyphenol oils?

Yes, but they require exceptional climate control and operator expertise. Modern mills make this easier and more consistent due to active temperature management and sealed processing chambers.

What is malaxation and why does it matter?

Malaxation is the slow mixing of crushed olive paste to help oil droplets merge into larger ones, improving separation efficiency. It typically lasts 15–45 minutes and must stay below 27°C. Longer malaxation increases yield but reduces aroma complexity and phenolic content, a trade-off between quantity and quality.

What is a two-phase vs. three-phase centrifuge?

Three-phase decanters add warm water to aid separation, which dilutes polyphenols into the aqueous phase and reduces phenolic content by 15–25%. Two-phase decanters eliminate water addition, preserving significantly more polyphenolic compounds, making them the preferred choice for premium extra virgin olive oil.

Conclusion: Science, Tradition, and Quality in Every Bottle

How olive oil is made, the extraction method chosen at the mill is one of the most consequential decisions in olive oil quality, though it is often hidden from consumer view. Whilst traditional stone-milling and cold-pressing methods carry historical prestige and produce excellent oils when executed with precision, modern centrifugal cold extraction is scientifically superior in controlling temperature, minimising oxidation, preserving polyphenols, and ensuring consistency.

For producers of early-harvest Greek extra virgin olive oil aiming for maximum polyphenol content and sensory complexity, modern centrifugal extraction combined with two-phase separation and rigorous temperature control is the optimal choice. The myth that “old methods are better” has been thoroughly refuted by peer-reviewed research, yet the romance of traditional production persists in marketing.

Understanding extraction methods empowers consumers to look beyond misleading marketing terms like “first cold pressed” and focus on what actually matters: harvest date, harvest stage (early vs. late), lab-verified polyphenol content, producer transparency about processing methods, and the overall reputation of the producer.

The best olive oil combines the best of heritage and science, traditional Greek olive cultivars like Koroneiki, harvested early for maximum phenolic richness, processed in modern mills with precise temperature control and two-phase centrifugation. This is the formula for oils that deliver authentic flavour, genuine health benefits, and the complexity that defines truly premium extra virgin olive oil.

Explore more about olive oil quality and production:

• Early harvest olive oil: Benefits, taste, and value
• High-polyphenol olive oil: Science-backed benefits
• The olive oil production process: From grove to bottle
• Greek olive oil vs Italian and Spanish
• How to choose high-quality olive oil
• The history of the olive tree