How Olive Oil Is Made: From Harvesting to Bottling

Olive oil production combines ancient tradition with modern science to create one of the world’s most cherished cooking ingredients. This golden liquid isn’t just any oil—it’s the pure juice extracted from olives, packed with flavor and health benefits. Understanding how olive oil transforms from fruit to bottle helps you appreciate the care, precision, and expertise behind every drop.

Understanding olive oil: the basics before we begin

Unlike most cooking oils made from seeds, olive oil comes directly from a fruit. This fundamental difference influences everything about its production, flavor, and nutritional profile.

The olive variety and growing conditions (“terroir”) play huge roles in the oil’s character. Just like wine grapes, olives absorb the essence of their environment—soil minerals, climate patterns, and sunshine levels all shape the final product.

Key polyphenols in olive oil and their significance

Polyphenols are powerful antioxidant compounds that give quality olive oil its distinctive taste and health benefits:

• Oleocanthal: Creates the peppery sensation that makes you cough; has anti-inflammatory properties similar to ibuprofen
• Oleuropein: Responsible for bitterness; offers antioxidant and antimicrobial benefits
• Hydroxytyrosol: One of the most powerful antioxidants found in nature; higher in early-harvest oils
• Tyrosol: Less potent than hydroxytyrosol but more stable during storage

The concentration of these compounds depends heavily on olive variety, harvest timing, and production methods. Oils with high polyphenol content (over 250mg/kg) offer more health benefits but might taste more bitter and pungent.

Step 1: Harvesting the olives – timing is everything

The olive harvest marks the beginning of the oil-making journey, and timing this step perfectly makes all the difference.

Optimal harvesting times

Farmers must decide whether to harvest early or late:

Most premium producers harvest when olives show a mix of green and purple—a sweet spot balancing flavor intensity with adequate oil content.

Harvesting methods

Traditional and modern approaches each offer distinct advantages:

Traditional harvesting:

• Hand-picking or using hand-held combs to rake olives onto nets
• Preserves fruit integrity with minimal damage
• Labor-intensive and costly
• Often used for premium oils where quality outweighs cost concerns

Modern harvesting:

• Mechanical tree shakers and over-the-row harvesters
• Much faster and more economical
• May cause more fruit damage
• Suitable for larger commercial operations

The race against time

After harvesting, a countdown begins. Quality-focused producers rush olives to the mill within 24 hours—ideally within 4-6 hours. Every passing hour risks fermentation, oxidation, and defects that compromise the oil’s quality. Premium producers often have mills on-site to minimize this critical time gap.

Regional harvest variations

Harvest timing varies significantly by region:

• Northern Hemisphere
  • Mediterranean Basin: October to January
  • California: November to January
• Southern Hemisphere
  • Australia/New Zealand: April to June
  • Chile/Argentina: March to May

This global variation means fresh olive oil is being produced somewhere in the world every six months.

Step 2: Preparation at the mill – cleaning and de-leafing

When olives arrive at the mill, they undergo inspection and preparation before processing.

The cleaning process removes leaves, twigs, and other debris through washing systems or air blowers. Modern facilities use vibrating screens and water baths to separate the olives from unwanted material.

This step isn’t merely about cleanliness—leaves and twigs can add harsh, woody flavors to the oil. Soil and other contaminants might introduce off-flavors or even safety concerns. Clean olives lead to pure-tasting oil that truly represents the fruit’s character.

Quality assessment at intake

Many quality-focused mills perform rapid tests on incoming olives:

• Visual inspection: Checking for mold, pests, or fruit damage
• Moisture content: Higher water content may indicate rain-soaked fruit
• Fruit temperature: Warm olives may have started fermenting
• Maturity index: Measuring the ratio of green to black olives

This initial assessment helps millers decide how to process each batch optimally. Some producers sort olives by variety, ripeness, or quality to create oils with specific profiles.

Step 3: Crushing the olives – creating the olive paste

Crushing breaks open the olive cells to release the precious oil inside. This rupturing process creates a paste that makes oil extraction possible.

Traditional method: stone mills

For thousands of years, olives were crushed using giant granite wheels rotating in stone basins:

• Crushes olives slowly and gently
• Generates minimal heat, preserving delicate aromas
• Creates a paste with specific consistency that many artisanal producers prefer
• Takes longer and risks more oxygen exposure if not managed carefully

Modern method: metal mills

Today’s producers typically use stainless steel hammer mills, disc mills, or blade crushers:

• Crushes olives quickly and efficiently
• Provides excellent control over paste consistency
• Reduces oxidation through faster processing
• Creates different particle sizes that may impact extraction efficiency

Some modern systems even remove pits before crushing. This practice can reduce bitter notes from the pit and prevent mechanical wear on equipment, though many traditional producers maintain that the pit contributes valuable antioxidants and flavor compounds.

Traditional vs. modern crushing: a comparison

Step 4: Malaxation – the crucial mixing stage that determines oil quality

Malaxation might be the least known yet most crucial step in olive oil production. This slow, continuous mixing of the olive paste allows tiny oil droplets to combine into larger ones that can be separated more easily.

The science behind malaxation

During crushing, olive oil exists as microscopic droplets trapped within ruptured plant cells. Malaxation breaks down cell walls through mechanical and enzymatic action, allowing these droplets to combine and separate from the water and solids.

Key factors during malaxation

Temperature Control:

• “Cold extraction” maintains temperatures below 27°C (80.6°F)
• Higher temperatures increase yield but destroy aromatic compounds and accelerate oxidation
• EVOO must be extracted at low temperatures to preserve its delicate flavors and health benefits

Duration:

• Typically ranges from 30-60 minutes
• Longer mixing increases yield but may reduce quality
• Too short and oil remains trapped; too long and oxidation occurs

Oxygen Exposure:

• Modern malaxers often use inert gas (nitrogen or argon) to displace oxygen
• Reduces oxidation that degrades flavor and nutritional value
• Preserves more polyphenols and vitamin E

The malaxer machine itself looks like a horizontal tub with slowly rotating metal blades that keep the paste moving gently without introducing air.

The expert’s perspective

“The malaxation phase is where the miller truly becomes an artist,” explains Maria Consuela Diaz, a third-generation master miller from Andalusia, Spain. “We make minute adjustments to temperature, time, and atmosphere based on each day’s olives. These small decisions ultimately determine whether an oil will be good or exceptional.”

Malaxation parameters by desired oil style

Step 5: Separating the oil – extracting the liquid gold

After malaxation, the paste contains three components that must be separated: olive oil, vegetation water, and solid materials (pomace).

Traditional method: pressing

The ancient method of extraction uses pressure to squeeze oil from the paste:

• Olive paste is spread on fiber discs called “fiscoli” or “mats”
• Discs are stacked and subjected to hydraulic pressure
• Oil and water seep out while solids remain trapped in the discs
• A second separation step divides the oil from the water

This method creates distinctive oils but has drawbacks including higher labor requirements, hygiene challenges, and lower yields.

Modern method: centrifugation

Most modern facilities use centrifuges to separate components based on their different densities:

Horizontal Centrifuge (Decanter) comes in two types:

1. Two-phase system:
   • Separates oil from everything else
   • Produces oil and wet pomace (combining solids with vegetation water)
   • Uses less water, creating fewer waste products
   • Better preserves polyphenols and other beneficial compounds
2. Three-phase system:
   • Separates oil, vegetation water, and pomace as distinct outputs
   • Requires adding water, which can wash away some water-soluble polyphenols
   • Creates more wastewater but produces drier pomace

Vertical Centrifuge (optional second centrifugation):

• Further “polishes” the oil by removing remaining water and fine particles
• Increases clarity and extends shelf life
• May remove some flavor compounds along with impurities

Some specialty producers use the Sinolea method (also called percolation or cold dripping), which works on the principle that oil adheres to metal plates dipped into the paste. This gentle method produces high-quality oil but yields less and requires more labor.

Traditional vs. modern production methods

Step 6: Further processing (for non-Virgin Oils)

Virgin olive oils (including extra virgin) go straight to filtering and bottling. Other grades require additional processing.

Refining process

When oils have defects or high acidity, refining can make them usable:

• Neutralization: Removes excess free fatty acids with alkali treatment
• Bleaching: Removes color impurities with filtering agents like bentonite or activated carbon
• Deodorization: Uses steam distillation to remove volatile compounds that cause off-flavors

These processes create neutral-tasting “refined olive oil” that lacks the flavor, aroma, and many health benefits of virgin oils. This refined oil is often blended with some virgin oil to create “Pure Olive Oil” or “Olive Oil” (not virgin) products.

The chemistry of refining: what gets lost

Pomace oil extraction

The solid waste (pomace) still contains some oil that can be extracted:

• Pomace is dried and treated with hexane or other solvents
• This dissolves the remaining oil, which is then separated from the solvent
• The resulting crude pomace oil must be refined before consumption
• Often labeled as “Olive Pomace Oil” in stores

Pomace oil represents the lowest quality category of olive-derived oils.

Step 7: Filtering (optional but common)

Many producers filter their fresh oil to remove suspended solids and moisture:

• Enhances clarity and visual appeal
• Extends shelf life by removing organic matter that could ferment
• May reduce some flavor intensity initially

Filtration typically uses materials like cotton, paper, cellulose, or diatomaceous earth.

Unfiltered oils (sometimes called “olio nuovo” when newly pressed) maintain tiny olive particles that provide intense flavor but shorten shelf life and create sediment at the bottom of the bottle. These oils may appear cloudy rather than clear.

Filtered vs. unfiltered: making the right choice

Step 8: Quality testing, grading, and storage

Before bottling, olive oil undergoes rigorous testing to determine its grade and quality.

Chemical analysis

Key tests include:

• Free fatty acidity: Measures breakdown of the oil (must be ≤0.8% for EVOO)
• Peroxide value: Indicates oxidation levels
• UV absorption: Detects processing methods and oxidation
• Polyphenol content: Measures beneficial antioxidants

Understanding chemical parameters: what they mean for consumers

Sensory analysis

Professional tasters evaluate oils for:

• Positive attributes: Fruitiness, bitterness, pungency
• Negative attributes: Rancidity, mustiness, fustiness, winey flavors

For EVOO certification, oils must have zero sensory defects and show positive olive attributes.

Common sensory defects and their causes

Proper storage

Once tested, oil needs proper storage conditions:

• Temperature-controlled environments (ideally 14-18°C/57-65°F)
• Protection from light (in tanks, dark rooms, or dark glass)
• Protection from oxygen (filled tanks with floating lids or inert gas)

The right storage conditions prevent premature aging and quality degradation.

Step 9: Bottling and labeling

The final step brings olive oil to the consumer.

Quality producers choose materials that protect the oil:

• Dark glass bottles block light that degrades oil
• Tin containers provide excellent light and oxygen barriers
• Some premium oils use ceramic containers

Labels should indicate:

• Oil grade (Extra Virgin, Virgin, etc.)
• Harvest date or best-by date
• Origin information
• Acidity level (sometimes)
• Production method information

How to read olive oil labels

Byproducts of olive oil production: what happens to the rest?

Olive oil production creates significant byproducts that present both challenges and opportunities.

Olive pomace

This solid waste finds various uses:

• Fuel for biomass energy
• Base material for pomace oil extraction
• Compost and soil amendments
• Animal feed component

Vegetation water

This liquid waste contains polyphenols and organic compounds:

• Traditionally problematic due to environmental impacts
• Modern applications include irrigation (after treatment)
• Source of valuable antioxidant compounds
• Biogas production through anaerobic digestion

Progressive producers implement closed-loop systems to minimize waste and maximize resource utilization.

Innovative byproduct applications

Regional production variations: a global perspective

Olive oil production varies significantly across regions, influencing characteristics of the final product.

Mediterranean traditional producers

Spain (world’s largest producer):

• Focuses on efficiency and volume
• Large-scale, highly mechanized operations
• Leading producer of Arbequina and Picual varieties
• Increasingly adopting early harvest techniques for premium markets

Italy:

• Emphasizes artisanal methods and regional diversity
• Many small producers with traditional approaches
• Famous for Tuscan oils (primarily Frantoio, Moraiolo, Leccino varieties)
• Strong connection between oil and local cuisine

Greece:

• Primarily Koroneiki variety
• Higher percentage of traditional stone mills still in operation
• Often produces oils with distinctive pungency
• Many family operations with generational knowledge

New world production regions

California:

• Modern, efficient facilities
• Strict quality standards and testing
• Blend of Mediterranean varieties with ideal growing conditions
• Focus on premium market segment

Australia:

• Pioneer in super-high-density planting systems
• Advanced mechanical harvesting
• Focus on science-based production methods
• Award-winning quality despite newer industry

Chile:

• Growing rapidly with Mediterranean climate
• Modern equipment with traditional influence
• Lower production costs
• Increasing focus on organic certification

Regional production methods and their impact

Home testing: evaluating olive oil quality like a pro

You don’t need a professional laboratory to assess olive oil quality. These simple tests can help you evaluate your purchases:

The sensory test

1. Pour about a tablespoon of oil into a small glass
2. Warm the glass by cupping it in your hands for about 30 seconds
3. Smell the oil, noting any fresh or unpleasant aromas
4. Taste a small amount, letting it coat your tongue
5. Look for three positive attributes:
   • Fruitiness: reminiscent of fresh or ripe olives
   • Bitterness: detected primarily on the tongue
   • Pungency: a peppery sensation in the throat that might cause a cough

Quality EVOO should have at least some level of all three positive attributes and no defects (mustiness, vinegar notes, rancidity).

The fridge test (indicative but not definitive)

Genuine extra virgin olive oil often (but not always) solidifies when refrigerated. Place a small amount in the refrigerator overnight:

• Complete solidification suggests higher monounsaturated fat content, typical of olive oil
• Remaining completely liquid doesn’t necessarily indicate poor quality or adulteration (some authentic varieties solidify less readily)

Flame test (not recommended)

Contrary to popular belief, the flame test (whether oil burns in a lamp) is not reliable for determining quality or authenticity.

Common olive oil myths

Conclusion

The journey from olive to oil represents thousands of years of human ingenuity—continually refined but still faithful to its origins. Each step in this process shapes the final product, creating a spectrum of flavors, aromas, and qualities.

When you understand how olive oil is made, you gain deeper appreciation for this culinary treasure. The care, expertise, and time invested in creating quality olive oil explain why the best versions command premium prices.

Next time you drizzle extra virgin olive oil over your food, remember the journey it took—from sun-drenched orchards through careful crushing, mixing, and extraction—to reach your table.

FAQs

What’s the difference between cold-pressed and cold-extracted?

“Cold-pressed” traditionally referred to oils produced using pressure methods without added heat. Today, most olive oil comes from centrifugation, not pressing, so “cold-extracted” more accurately describes modern methods. Both terms mean the oil was processed below 27°C (80.6°F).

How long does it take to make olive oil?

Quality olive oil production typically takes 24-48 hours from harvest to extraction. The actual milling and extraction process might last only 1-2 hours, but the entire journey from tree to bottle—including testing, potential filtering, and bottling—can take several weeks.

Can I make olive oil at home?

While technically possible with small-scale equipment, home production rarely achieves the quality of professional operations. Commercial mills can process olives quickly after harvest and control critical factors like temperature and oxygen exposure more effectively.

Why is some olive oil green and some golden?

Color primarily depends on olive ripeness at harvest. Green oils typically come from early-harvested fruit with higher chlorophyll content, while golden oils usually come from riper olives. Olive variety and filtration also affect color.

What makes Extra Virgin Olive Oil special?

EVOO represents the highest quality standard, meeting strict chemical criteria and passing expert taste evaluation with zero defects. It’s produced solely through mechanical means without heat or chemicals, preserving maximum flavor and nutritional benefits.

How should I store olive oil at home?

Store your olive oil:
• Away from light (in a cupboard or in dark glass bottles)
• Away from heat (not next to the stove)
• At moderate temperature (55-75°F/13-24°C is ideal)
• Tightly sealed to prevent oxygen exposure
• For no more than 1-2 years, ideally using it within 6 months of opening

Is more expensive olive oil always better?

Not necessarily. While quality production does incur higher costs, price also reflects packaging, marketing, and retail margins. Many excellent oils are available at moderate prices, while some expensive oils may be overpriced for their quality. Learning to evaluate oil yourself is more reliable than using price as your only indicator.

What’s the smoke point of olive oil? Can I cook with it?

Extra virgin olive oil has a smoke point of approximately 350-410°F (175-210°C), making it suitable for most cooking methods including sautéing, baking, and even many types of frying. Refined olive oil has a slightly higher smoke point (about 470°F/240°C), making it especially suitable for high-heat cooking.

What does “first press” or “first cold press” mean?

These terms originated when oils were actually pressed. “First press” meant the initial pressing of the olive paste, yielding the highest quality oil. Today, with centrifugal extraction, these terms are mostly marketing language suggesting premium quality. All extra virgin olive oil is technically “first press” and “cold-pressed” by definition.