How polyphenol content is measured
Polyphenol content is typically expressed in milligrams per litre (mg/L) or milligrams per kilogram (mg/kg). The figures describe the total amount of polyphenols in the oil at the time of analysis.
The unit of measurement
Polyphenol content is typically expressed in milligrams per litre (mg/L) or milligrams per kilogram (mg/kg). The figures describe the total amount of polyphenols in the oil at the time of analysis.
It's worth bearing in mind that polyphenol content is not static. It decreases gradually after pressing, and factors such as light, heat and storage time influence how quickly this happens. A measured value is therefore a snapshot in time, not a permanent guarantee.
The HPLC method
The most common and reliable method for measuring polyphenols in olive oil is HPLC (High-Performance Liquid Chromatography). The method separates and quantifies individual polyphenol compounds, providing a detailed picture of the oil's composition.
HPLC analysis is carried out by specialised laboratories and is regarded as the industry standard. It is the method that the European Food Safety Authority (EFSA) references in its assessment of olive oil polyphenols.
Other methods
There are simpler and cheaper analysis methods, such as Folin-Ciocalteu, which measure total phenolic content more broadly. These can be useful as an initial indication but are less precise and may give higher values than HPLC.
When comparing polyphenol levels between different olive oils, it's therefore important to know which method was used. A figure without a stated method is difficult to interpret.
Why measurements can vary
Even within the same batch, measurements can differ slightly depending on when the sample was taken and how it was handled before analysis. In addition, polyphenol content naturally decreases over time after pressing.
This means that an oil measuring 900 mg/L shortly after pressing may come in lower after a few months. That doesn't mean the oil is inferior, only that the polyphenols gradually break down, exactly as expected.
Transparency about measurement method, timing and laboratory gives a more accurate picture of the oil's quality. That's one of the reasons we always report the analysis method and values per batch.