Processing & Production Methods
How harvest and extraction techniques preserve or destroy polyphenols
The Critical Window
Even olives with the highest genetic potential can lose 50-80% of their polyphenols through poor processing. The time between harvest and bottling is critical—every hour of delay, every degree above optimal temperature, and every exposure to oxygen degrades antioxidant content.
Key Principle: High-quality producers treat olive oil extraction like emergency medicine—speed, precision, and sterile conditions are non-negotiable.
1. Harvest Timing - The Most Critical Decision
Early vs. Late Harvest Impact
Early Harvest (Green)
October - Early November
- ✓ Polyphenols: 600-1000+ mg/kg
- ✓ Chlorophyll: High (green color)
- ✓ Stability: Excellent (2+ year shelf life)
- ✓ Flavor: Intensely bitter/peppery
Trade-off: Only 10-15% oil yield. Expensive to produce.
Mid Harvest (Turning)
Late November
- ✓ Polyphenols: 350-600 mg/kg
- ✓ Color: Yellow-green
- ✓ Stability: Good (18-month shelf life)
- ✓ Flavor: Moderate bitterness, fruity
Trade-off: 18-22% yield. Balanced approach.
Late Harvest (Ripe/Black)
December - January
- ✗ Polyphenols: 150-350 mg/kg
- ✗ Color: Golden yellow
- ✗ Stability: Poor (6-12 month shelf life)
- ✗ Flavor: Mild, buttery, no pepper
Why producers do it: 25-30% yield. Maximum profit.
Polyphenol Degradation During Ripening
As olives ripen, enzymes break down polyphenols to make fruit palatable. This natural process happens whether olives stay on the tree or after harvest.
Critical Window: Green olives lose approximately 50-100 mg/kg polyphenols per week during late ripening stages. This is why harvest date matters more than any other factor.
2. Harvest-to-Mill Time - The Race Against Oxidation
Once picked, olives begin to ferment and oxidize. Polyphenols degrade rapidly:
0-4 Hours (Elite Standard)
Polyphenol Retention: 95-100%
Premium producers mill immediately. Some have mobile mills in groves.
4-12 Hours (Acceptable)
Polyphenol Retention: 85-95%
Acceptable if olives kept cool and ventilated. Most quality producers meet this standard.
12-24 Hours (Marginal)
Polyphenol Retention: 70-85%
Fermentation begins. Noticeable quality loss. Common in mass-market production.
24+ Hours (Poor Quality)
Polyphenol Retention: <70%
Significant oxidation and fermentation. May develop defects (musty, fermented flavors).
Red Flag: If a producer doesn't prominently display their harvest-to-mill time, assume it's longer than optimal. Transparency is a quality indicator.
3. Extraction Method & Temperature Control
Modern Continuous Extraction (Preferred)
Two-phase or three-phase centrifugal systems. Crushes olives into paste, then separates oil via centrifuge.
Advantages:
- ✓ Continuous process (no batches, less oxidation)
- ✓ Precise temperature control (digital monitoring)
- ✓ Shorter processing time (30-45 minutes)
- ✓ Nitrogen flushing capability
- ✓ Easy cleaning (prevents cross-contamination)
Industry Standard: Most premium producers use continuous extraction kept below 25°C.
Traditional Stone Mill (Artisanal)
Granite wheels crush olives, then paste is pressed between fiber mats. Centuries-old method.
Considerations:
- ± Slower process (1-2 hours)
- ± More oxygen exposure
- ± Temperature harder to control
- ± Labor intensive
- + Can produce exceptional oil when done correctly
Reality: Stone mill is romantic but not inherently better. Quality depends on operator skill and temperature management.
Temperature: The Make-or-Break Factor
<25°C (77°F) - Elite Standard
Maximum polyphenol preservation. Premium producers often target <23°C. Lower oil yield but maximum quality. Look for "cold extracted" or temperature certification on labels.
25-27°C (77-80°F) - Standard "Cold Pressed"
EU legal limit for "cold pressed" designation. Acceptable but near the edge. Some polyphenol loss but still produces quality EVOO.
>27°C (>80°F) - Avoid
Significant polyphenol degradation. Enzymes denature. Cannot legally be called "cold pressed". Common in mass-market production to maximize yield.
Why Temperature Matters: Heat increases oil yield by 5-10% but destroys polyphenols and volatile aromatic compounds. Every degree above 25°C accelerates degradation exponentially.
4. Storage & Packaging
Post-Extraction Protection
Optimal Storage Conditions:
- ✓Temperature: 12-18°C (54-64°F) constant
- ✓Light: Complete darkness or UV-blocking tanks
- ✓Oxygen: Nitrogen-flushed stainless steel tanks
- ✓Bottling: On-demand to minimize bottle age
Packaging Best Practices:
- ✓Dark glass: Protects from UV light damage
- ✓Metal tins: Complete light and oxygen barrier
- ✓Bag-in-box: Excellent for bulk, prevents oxidation
- ✗Clear glass: UV destroys polyphenols rapidly
- ✗Plastic bottles: Allows oxygen permeation
Polyphenol Degradation Over Time
Even in optimal conditions, EVOO loses approximately 10-15% polyphenols per year:
- • Year 1: 90-95% retention (excellent)
- • Year 2: 75-85% retention (good)
- • Year 3: 50-70% retention (acceptable for cooking only)
Takeaway: Buy current harvest only. Use within 12-18 months of harvest date.
Quality Processing Indicators - What to Look For
Harvest Date on Label
Premium producers prominently display harvest month/year. Absence is a red flag.
"Cold Extracted" or Temperature Certification
Look for <25°C or <27°C certification. Some producers specify exact temperature.
Harvest-to-Mill Time Statement
Elite producers advertise "2-hour harvest-to-press" or similar. Shows quality commitment.
Polyphenol Test Results
Best-in-class producers provide lab certificates with exact mg/kg polyphenol content.
Dark Glass or Metal Packaging
Protects from light. Clear bottles indicate producer doesn't understand polyphenol preservation.
Single Estate or PDO/DOP Certification
Indicates control over entire production chain from grove to bottle.
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