On a label, a product page or a laboratory report, acidity is often the first figure people look at. It is useful, but often misunderstood. Here is what it measures, what makes it rise, what the regulations say, and why low acidity alone does not make a good oil.
What free acidity measures
Free acidity corresponds to the proportion of fatty acids that have become detached from triglycerides, the molecules that make up most of the oil. This detachment is called hydrolysis. The official method is a laboratory titration, and the result is expressed as a percentage of oleic acid (Cayuela-Sánchez, Grasas y Aceites, 2021). A result of 0.30% therefore means 0.30 g of free fatty acids, expressed as oleic acid, per 100 g of oil, as stated in the International Olive Council standard (IOC, trade standard, Rev. 22, 2026).
An important point: you cannot taste this figure. A technical document from the University of California (UC ANR) states it clearly: free fatty acids cannot be perceived in the mouth, at least not at the levels usually present in oil (Vossen, UC ANR). The same document describes acidity as a "rough" indicator of quality, linked to how the fruit was handled before reaching the mill.
What makes acidity rise
Acidity originates in the fruit, before extraction. The available studies point to several factors:
- The time and conditions of olive storage. In an Italian study, the acidity of one oil rose from 0.28% to 1.31% after the olives had been stored for 12 days at 25 °C, compared with 0.51% at 4 °C. For another variety, it rose from 0.42% to 2.64% at 25 °C (Piscopo et al., Emirates Journal of Food and Agriculture, 2018).
- Damaged fruit. In an olive whose tissues are ruptured, enzymes release the fatty acids (Brkić Bubola et al., Foods, 2020). The same authors note that storage that is too warm encourages the growth of micro-organisms in the fruit.
- Advanced ripeness. Storage at high temperature speeds up ripening and softens the tissues, making them easier to rupture, which can encourage hydrolysis (Brkić Bubola et al., 2020). Piscopo et al. also observe that olives harvested later deteriorate more quickly.
Legal limits by category
In the European Union, the limits are set out in Annex I to Delegated Regulation (EU) 2022/2104:
| Category | Free acidity (% oleic acid) |
|---|---|
| Extra virgin olive oil | ≤ 0.80 |
| Virgin olive oil | ≤ 2.0 |
| Lampante olive oil | > 2.0 |
| Refined olive oil | ≤ 0.30 |
| Olive oil composed of refined olive oils and virgin olive oils | ≤ 1.00 |
| Crude olive pomace oil | no limit |
| Refined olive pomace oil | ≤ 0.30 |
| Olive pomace oil | ≤ 1.00 |
The IOC trade standard uses the same thresholds for extra virgin (0.80) and virgin (2.0) oils, but also provides for an "ordinary virgin" category up to 3.3%, with lampante oil beginning above that (IOC, 2026).
Necessary, but not sufficient
An oil with 0.2% acidity is not necessarily extra virgin. For this category, Regulation 2022/2104 also sets, among other things:
- a peroxide value ≤ 20 mEq O2/kg, an indicator of primary oxidation;
- ultraviolet absorbance values K232 ≤ 2.50, K270 ≤ 0.22 and ΔK ≤ 0.01, finer indicators of oxidation;
- an assessment by a tasting panel: median of defects equal to 0 and median of fruitiness greater than 0.
Field data confirm this. In a UC Davis Olive Center study of 260 samples, almost all met the acidity limit, but 141 failed the sensory assessment (Flynn, Li and Wang, UC Davis Olive Center, 2014). To learn how to recognise these defects, see our article on olive oil defects, and to read a full report, our guide on how to read a laboratory analysis.
Key points
- Free acidity measures detached fatty acids, expressed as oleic acid. It is measured in the laboratory, not in the mouth.
- It mainly tells you about the condition of the olives and the time before they reached the mill.
- Extra virgin: 0.80% maximum. But low acidity on its own says nothing about oxidation or sensory defects.
Common misconceptions
"It's peppery, so it's acidic"
No. For the IOC, bitterness and pungency are positive attributes. Bitterness is a characteristic taste of oils made from green olives or olives turning colour; pungency is a tactile sensation typical of oils made early in the season from olives that are still fairly unripe (IOC, method for the organoleptic assessment, Rev. 11, 2024). They have nothing to do with free acidity, which cannot be tasted.
"Acidity < 0.5%" on the label as a guarantee of quality
This type of statement is regulated. Article 10, point (d), of Delegated Regulation (EU) 2022/2104 provides that the maximum acidity expected by the date of minimum durability may only be shown if it is accompanied, in characters of the same size and in the same field of vision, by the maximum values for peroxide value, wax content and ultraviolet absorption expected by the same date. The Food Safety Authority of Ireland presents the rule in the same way (FSAI). An acidity figure on its own is therefore both incomplete and, on a label, non-compliant. For the rest of the label information, see how to read an olive oil label.
And at Oikos Antalis?
At Oikos Antalis, our Koroneiki olives come from four family estates in Ilia, in the Peloponnese. They are harvested by hand and cold extracted on the same day, which limits the time between harvest and mill. We publish our full laboratory reports on the Analyses page. The free acidity measured there is 0.33% for Skourochori and 0.42% for Agios Ilias (2026 harvest), and 0.19% for Paliovarvassena (2025 harvest). These figures should be read together with the other parameters shown on each report, in keeping with the spirit of the European rule. Our oils are available in the Bottles collection.
FAQ
Can you smell or taste the acidity of an olive oil?
No, not at the levels usually present. A laboratory analysis is needed (Vossen, UC ANR).
Is an oil at 0.1% better than an oil at 0.4%?
Not necessarily. Both meet the 0.80% limit. Quality also depends on oxidation (peroxides, K232, K270) and on the tasting panel's verdict.
Does acidity change after bottling?
The regulation refers to acidity "expected by the date of minimum durability", which implies that a value measured at a given moment is not fixed. This is why a dated, complete report is more informative than a single figure.
Sources
- Commission Delegated Regulation (EU) 2022/2104 as regards marketing standards for olive oil (consolidated version), European Commission, EUR-Lex, 2022
- Trade Standard Applying to Olive Oils and Olive Pomace Oils, COI/T.15/NC No 3/Rev. 22, International Olive Council, 2026
- Sensory Analysis of Olive Oil: Method for the Organoleptic Assessment of Virgin Olive Oil, COI/T.20/Doc. No 15/Rev. 11, International Olive Council, 2024
- Captive fatty acids of fresh olive oils?, J.A. Cayuela-Sánchez, Grasas y Aceites, 2021
- Effect of olive storage temperature on the quality of Carolea and Ottobratica oils, Piscopo et al., Emirates Journal of Food and Agriculture, 2018
- Olive Fruit Refrigeration during Prolonged Storage Preserves the Quality of Virgin Olive Oil Extracted Therefrom, Brkić Bubola et al., Foods, 2020
- Description of Olive Oil Analyses Tests, P. Vossen, University of California Agriculture and Natural Resources, n.d.
- Correlating olive oil sensory and chemistry results, Flynn, Li and Wang, UC Davis Olive Center, 2014
- Olive Oil, Food Safety Authority of Ireland, accessed 2026