by Dan Kollias, Kollias Olive Oil
Not all extra virgin olive oils are the same, and quality cannot be reduced to a single number.
Laboratory testing can tell us a lot. It can show how the olives were handled before pressing, whether the oil has begun to oxidize, whether the oil meets the standards for extra virgin olive oil, and how much of its naturally occurring phenolic content remains.
At Kollias Olive Oil, we test our oil each harvest and publish the results. Below, we explain the most important measurements and compare our 2023, 2024 and 2025 harvests side by side.
What makes an extra virgin olive oil high quality?
Extra virgin olive oil is the highest recognized grade of virgin olive oil. Under International Olive Council standards, EVOO must satisfy chemical requirements, such as free acidity of no more than 0.8 grams per 100 grams, as well as sensory requirements, such as smell and taste.
But meeting the legal definition of “extra virgin” is only the starting point. Two oils can both qualify as EVOO and still differ considerably in freshness, flavor, antioxidant content and resistance to oxidation.
That is why we look at several measurements together rather than relying on one number alone.
Key takeaways
- Kollias remained consistently low in acidity across the 2023, 2024, and 2025 harvests, measuring 0.358%, 0.34%, and 0.35% respectively.
- Biophenol levels remained substantial across all three harvests: 410 mg/kg in 2023, 453 mg/kg in 2024, and 377 mg/kg in 2025.
- Peroxide and UV absorption measurements stayed within the applicable limits for extra virgin olive oil in each year tested.
- Quality varies naturally from harvest to harvest, so no single number tells the whole story; acidity, peroxide value, UV measurements, polyphenols, freshness, and processing should be considered together.
Kollias laboratory results: 2023–2025
| Harvest | Biophenols* | Acidity | Peroxide Value | K232 | K268 | ΔK |
|---|---|---|---|---|---|---|
| 2023 | 410 mg/kg | 0.358% | 4.1 | 1.50 | 0.113 | -0.001 |
| 2024 | 453 mg/kg | 0.34% | 11.8 | 1.78 | 0.16 | 0.00 |
| 2025 | 377 mg/kg | 0.35% | 8.1 | 1.46 | 0.14 | -0.00 |
*The laboratories report this measurement as biophenols (as tyrosol). It is commonly discussed more broadly as the polyphenol content of olive oil.
The 2023 phenolic analysis reported 410 mg/kg of biophenols, together with individual phenolic compounds including oleacin (103 mg/kg) and oleocanthal (91 mg/kg).
The 2024 harvest measured 453 mg/kg polyphenols, 0.34% acidity, a peroxide value of 11.8, K232 of 1.78, K268 of 0.16, and ΔK of 0.00. See also our full 2024 laboratory results.
The 2025 harvest measured 377 mg/kg biophenols, 0.35% acidity, peroxide value 8.1, K232 1.46, K268 of 0.14, and ΔK of -0.00.
What are polyphenols in olive oil?
Polyphenols are naturally occurring compounds found in olives. In extra virgin olive oil, they contribute to both flavor and oxidative stability ("shelf life").
Oils with higher phenolic content often have more noticeable bitterness and “pungency,” which refers to the peppery sensation sometimes felt in the back of the throat. University of California-Davis notes that fruitiness, bitterness and pungency are among the positive sensory characteristics associated with extra virgin olive oil. In other words, it's a good thing!
Phenolic content can vary substantially from one olive oil to another. One of the factors that can influence it is the variety of olive. Greek Koroneiki olives like the ones we grow are typically higher in phenolic content than other varieties. Other factors can include climate, irrigation, degree of ripeness, harvest timing and processing methods.
Having said all of that, there is no official minimum total-polyphenol level required for an oil to qualify as extra virgin. That is why the phrase “high-polyphenol olive oil” should not be treated as an official EVOO grade. It is more of a descriptor of an olive oil's flavor and antioxidant properties.
Why do early-harvest olive oils tend to contain more polyphenols?
Green olives harvested earlier in the ripening process generally produce less oil than fully ripe, purplish-black olives. However, pressing green olives yields more of the bitter, pungent and phenolic characteristics associated with fresh early-harvest EVOO. Kollias Olive Oil is produced from Koroneiki olives harvested early in the season (November) on our family farm in Filiatra, Greece and pressed promptly after harvest.
Other factors matter too, including cultivar, climate and processing. Polyphenol content should therefore be viewed as one part of the overall quality picture, not as a stand-alone score.
Learn more about polyphenols, health, and flavor. See also our article: "What is ‘Early Harvest’ Olive Oil and Why Should I Care?"
What does olive oil acidity mean?
“Acidity” in olive oil does not describe how sour the oil tastes.
Laboratory acidity measures the amount of free fatty acids in the oil, expressed as oleic acid. Extra virgin olive oil may contain no more than 0.8% free acidity under IOC standards.
Lower acidity is generally associated with healthy fruit and careful handling before and during processing. Damage to olives, delays before milling and poor storage conditions can contribute to deterioration.
Across the three Kollias harvests shown above, acidity remained remarkably consistent:
- 2023: 0.358%
- 2024: 0.34%
- 2025: 0.35%
All three were well below the 0.8% threshold to be considered EVOO.
Read our deeper explanation of olive oil acidity.
What is peroxide value?
Peroxide value measures products formed during the early stages of oxidation. Oxidation is one of the principal ways olive oil loses freshness over time. Exposure to oxygen, heat and light can accelerate the process.
For each of the last three years, Kollias measured well below the EVOO limit of 20 meq O₂/kg:
- 2023: 4.1
- 2024: 11.8
- 2025: 8.1
These results can be summarized in one word: freshness.
What are K232, K268 and ΔK?
These measurements come from ultraviolet spectrophotometric testing. That's a mouthful, but in simple terms, testing olive oil with UV light waves can reveal chemical changes associated with oxidation, aging, refining, or other departures from the profile expected of extra virgin olive oil. In other words, these tests look for evidence that an olive oil has been blended with inferior oils or is old. They are part of the broader chemical profile used to determine whether an oil meets extra virgin standards.
For our 2025 sample, the lab tests reported:
- K232: 1.46, against a stated EVOO maximum of 2.50
- K268: 0.14, against a stated EVOO maximum of 0.22
- ΔK: -0.00, against a stated maximum of 0.01
The 2023 and 2024 harvests likewise tested within the limits reported with their respective analyses. In short, these laboratory results mean that our olive oil is pure and fresh.
Does a higher polyphenol number always mean better olive oil?
Technically, the answer is no. A high-quality EVOO should also have sound fruit, proper processing, low oxidation, acceptable acidity, good sensory characteristics and proper storage.
That is why we do not view the 2024 harvest as automatically “better” than 2023 or 2025 simply because its measured phenolic content was higher.
Instead, the three-year results show something more useful: consistency.
Kollias measured:
- 410 mg/kg in 2023
- 453 mg/kg in 2024
- 377 mg/kg in 2025
At the same time, acidity remained around one-third of one percent in all three years.
Harvest-to-harvest variation is normal in an agricultural product. What matters is whether the oil continues to meet strong quality benchmarks across multiple measurements.
What about the health benefits of olive oil polyphenols?
Unlike the European Union, the United States does not have a specific health claim based on any defined polyphenol measurement in olive oil. However, European Union rules allow olive oil producers to make a very specific health claim when the oil contains at least 5 mg of hydroxytyrosol and its derivatives per 20 grams of olive oil. The permitted claim is that olive oil polyphenols contribute to the protection of blood lipids from oxidative stress.
Because we sell our olive oil in the United States and not in Europe, we don't pay for the hydroxytyrosol and derivatives test every year. However, in 2023 we did. That year, our laboratory certificate reported 6 mg per 20 g of hydroxytyrosol and its derivatives, exceeding that stated threshold.
That does not mean polyphenol concentration should be viewed as a medical treatment or as the sole reason to choose an olive oil. It is one scientifically measurable characteristic of a high-quality EVOO.
Why publish olive oil laboratory results?
Consumers often see terms such as “premium,” “cold pressed,” “early harvest” and “high polyphenol,” but those descriptions are much more meaningful when accompanied by objective measurements. Publishing our results allows customers to see the same data we see.
It also demonstrates something that is easy to overlook. Olive oil is a fresh agricultural product. Each harvest is different. Weather, olive maturity and growing conditions vary from year to year. The goal is not to produce identical numbers every season. The goal is to establish a process that preserves quality, from picking through pressing, bottling and delivery.
How should you evaluate an olive oil?
Of course, flavor and aroma are the most important. But there are objective facts that matter. When comparing extra virgin olive oils, consider whether the producer is transparent about the following factors:
- Harvest date and freshness
- Origin and traceability
- Free acidity
- Peroxide value
- UV absorption measurements
- Polyphenol content
- How quickly the olives were pressed after harvest
- How the finished product is protected from heat, light and oxygen
Freshness matters especially because olive oil quality declines over time. UC Davis recommends paying attention to harvest dates and storing olive oil in a cool, dark place.
Three harvests, one standard
The laboratory results from 2023, 2024 and 2025 show natural year-to-year variation, while also demonstrating consistency in the characteristics we care about most.
Across all three harvests, Kollias remained low in acidity and substantial in phenolic content, with the broader chemical measurements supporting its classification as extra virgin olive oil.
For us, laboratory testing is not simply a marketing exercise. It is one way of documenting what happens when good fruit, careful harvesting, prompt milling and proper storage come together.
See our current harvest of Kollias Single Source Early Harvest Extra Virgin Olive Oil.
