Reading the olive oil label: acidity, polyphenols, peroxides explained

In front of an extra virgin olive oil bottle, most people look at two things: price and bottle appearance. Those who know a little also check cultivar and DOP zone. But the truly diagnostic numbers — those that tell you whether the oil is fresh, well extracted and rich in antioxidants — are in the analytical parameters. And those numbers aren't difficult to understand: you can learn them in five minutes.

In this guide we take the three key parameters (free acidity, total polyphenols, peroxide value) and see what they really say, what thresholds to look for and why a serious producer should declare them without theatrics.

Free acidity: the thermometer of olive quality

Free acidity measures the percentage of free fatty acids in the oil. It's expressed as a percentage of oleic acid (e.g. 0.2%, 0.5%).

What pushes it up:

• Damaged olives before milling (fallen to the ground, bird-pecked, attacked by olive fruit fly)
• Excessive time between harvest and milling (more than 24 hours = problems)
• High temperatures during olive storage before crushing
• Poor conservation of the oil after extraction

In other words: acidity tells you about the supply chain, not the flavour.

Thresholds to know:

• ≤ 0.8%: legal limit to be called "extra virgin" (EU category)
• ≤ 0.5%: limit for most Italian DOPs
• ≤ 0.3%: quality zone — the sign of healthy olives harvested and milled the same day
• ≤ 0.2%: excellence — only possible with selective harvest and milling within 6 hours

A producer publishing "acidity: 0.18%" is saying: I harvested intact olives, took them to the mill within hours, stored in stainless at controlled temperature. Technical info that has value only if verifiable (recent lab analyses on a specific lot).

What acidity does NOT tell you: flavour. An oil with 0.2% acidity can be insipid if the olives were polyphenol-poor. An oil with 0.4% can be stunning if the cultivar is right and harvest timing perfect.

Total polyphenols: the antioxidants you feel in your throat

Polyphenols (and especially secoiridoids like oleocanthal and oleacein) are the aromatic and antioxidant compounds of extra virgin olive oil. They are what you feel as bitterness and pungency at the back of the mouth, and the reason EVO has scientifically recognised nutraceutical properties (oleocanthal has anti-inflammatory activity similar to ibuprofen).

They are measured in mg/kg (sometimes written as ppm or "mg of tyrosol equivalent").

Useful thresholds:

• < 250 mg/kg: "light" oil, often from low-polyphenol cultivars (Verdese, some blends)
• 250 – 400 mg/kg: medium — Moresca, young Coratina, balanced blends
• 400 – 700 mg/kg: high — Tonda Iblea, Coratina, Nocellara del Belice in good years
• > 700 mg/kg: excellence — selected monocultivars, lucky vintages

Regulatory bonus: EU Regulation 432/2012 allows the claim "olive oil polyphenols contribute to the protection of blood lipids from oxidative stress" on the label only if the oil contains at least 5 mg/20 g of hydroxytyrosol and derivatives (~250 mg/kg total polyphenols). If you see this claim, the oil is certified above that threshold.

Practical knowledge: polyphenols decline over time. An oil at 600 mg/kg when freshly bottled may be at 350 after 18 months even if well kept. That's why harvest year matters so much.

Peroxide value: the oxidation index

The peroxide value measures how much the oil has already oxidised. It's expressed in meq O₂/kg (milliequivalents of oxygen per kilo).

What raises it:

• Light exposure
• Oxygen exposure (bottles open for months, non-airtight caps)
• High storage temperatures
• Time — even with perfect storage, it slowly rises

Thresholds:

• ≤ 20 meq O₂/kg: legal limit for "extra virgin"
• ≤ 12 meq O₂/kg: typical of well-kept oils, premium tier
• ≤ 8 meq O₂/kg: very fresh and well-stored, top of the range
• > 20 meq O₂/kg: downgraded to "virgin olive oil" (no longer extra virgin)

A freshly pressed and well-stored oil typically sits below 5 meq. You find it above 12 after a few months of commercial life.

Combined reading: low acidity + low peroxides = oil born well and well kept. Low acidity + high peroxides = oil born well but suffering in storage (light, heat, oxygen).

Bonus: what to look for in sensory analysis (panel test)

For the "extra virgin" category, EU Regulation 2568/91 also requires a panel test: certified tasters declare the median value of fruitiness and the absence of defects on a 0–10 scale.

What to look for in a technical sheet:

• Median fruitiness (Mf) > 0 → required for extra virgin
• Median defects (Md) = 0 → no perceived defect (rancid, fusty, muddy, mouldy, etc.)

A premium oil typically has a declared fruitiness 5–8 (intense) or 2–4 (medium-light) depending on the cultivar. Defects = 0 always.

Quick reference table

Parameter	Excellence threshold	"Good" threshold	Legal limit
Free acidity	≤ 0.2%	≤ 0.5%	≤ 0.8%
Total polyphenols	≥ 500 mg/kg	≥ 250 mg/kg	n/a
Peroxide value	≤ 8 meq O₂/kg	≤ 12 meq O₂/kg	≤ 20 meq O₂/kg
Median defects	0	0	0 (=extra virgin)
Median fruitiness	≥ 4	≥ 2	> 0

Where do I find these numbers?

Three places, in order of reliability:

1. The bottle label — the most transparent producers report at least acidity and harvest year
2. The lot's technical sheet — available online or on request from serious producers (PDF with lab analyses)
3. DOP/IGP certification — consortia publish panel tests and parameters for each certified lot

If a producer doesn't provide them even on request, that's not a good sign. If they publish them in detail, they're saying: "my olives speak for themselves".

Putting it together

When you look at a bottle of extra virgin olive oil, the four key questions in order of importance are:

1. When were the olives harvested? (Year)
2. What's the free acidity? (Supply chain)
3. What's the polyphenol content? (Antioxidants, flavour, stability)
4. What's the peroxide value? (State of conservation)

Clear answers to these four questions = oil that deserves your pantry. Vague answers = marketing covering for the product.

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Every Tenuta Chiaramonte oil comes with a technical sheet including lab analyses for the specific lot, harvest year and declared cultivar. Visit the shop to see the specs of each oil.