What the lab values tell you
Acidity, peroxide, K232, K270, Delta-K and polyphenols — what each number actually reveals.
6 min read
The numbers on an analysis report can look intimidating. In fact each one tells a different part of the oil's story: how sound the fruit was, how long it waited, even whether it is pure.
Free acidity (% oleic acid)
The proportion of free fatty acids in the oil. When olives are bruised, spoiled or left waiting after harvest, the oil molecules break down and this figure rises. Low acidity shows sound fruit processed quickly.
Limit: ≤ 0.8% for extra virgin. Acidity has no direct effect on taste — "acidic oil tastes sour" is a common misconception; acidity cannot be judged by palate, only measured in a laboratory.
Peroxide value (meq O₂/kg)
Measures how much oxygen the oil has been exposed to — an indicator of primary oxidation. A high figure usually points to a problem in pressing, filling or storage. Limit: ≤ 20.
K232
Specific absorbance measured under ultraviolet light at 232 nm. It catches the first stage of oxidation — it can show that deterioration has begun even while the peroxide value is still low. Limit: ≤ 2.50.
K270
Measured at 270 nm, it indicates secondary oxidation: the presence of breakdown products such as aldehydes and ketones. It is also sensitive to refined oil being blended in. Limit: ≤ 0.22.
Delta-K (ΔK)
Calculated from absorbances at several wavelengths. This is the adulteration test: it exposes whether refined oil has been blended into virgin oil. The limit is very tight — ≤ 0.01. Exceeding it raises doubt about purity.
Total polyphenols (mg/kg)
Unlike the others, higher is better here. Polyphenols are the oil's natural antioxidants; they extend shelf life and give that characteristic bitterness and peppery catch at the back of the throat. Early-harvest oils are markedly higher.
The health claim approved by the European Food Safety Authority (EFSA) requires at least 5 mg of hydroxytyrosol and its derivatives per 20 g of oil — roughly the 250 mg/kg level.
Where can I get these measured?
Bring your sample to our facility; we measure free acidity, K232, K270 and Delta-K free of charge and hand you the report.
Want your own oil measured?
See what you have just read in your own oil. Bring a sample and we will measure free acidity, K232, K270 and Delta-K free of charge.