That climate influences the composition of olive oil was a shared intuition across the sector, backed by isolated studies covering two or three harvests. What was missing was a long series. The paper Impact of meteorological conditions on fatty acid composition and isotopic signatures in Slovenian extra virgin olive oil: A long-term study, published open access in the journal Food Chemistry (vol. 525, 2026), provides one: 27 consecutive years and 1,643 authentic extra virgin olive oil samples, collected directly at the mill with full traceability from grove to final product.
The database comes from the Institute for Oliveculture at the Science and Research Centre Koper (Slovenia), and the research team is international: the University of Florence and Italy's CNR, the Jožef Stefan Institute in Ljubljana — home of corresponding author Nives Ogrinc — and the Andalusian Institute of Agricultural and Fisheries Research and Training (IFAPA) in Córdoba, represented by José Manuel Moreno-Rojas.
Eight percentage points of oleic acid between the coldest and the warmest year
Oleic acid remained the dominant fatty acid across every harvest, ranging from 78.87% in 1996 — one of the coldest years in the series, with a mean temperature of 12.7 °C and only 8 days above 30 °C — to 71.88% in 2018, one of the warmest harvests. The 2018 and 2019 oils recorded oleic acid levels 8.9% and 7.4% lower, respectively, than those of 1996.
Moving in the opposite direction, and again comparing 2018 with 1996, palmitic acid rose by 23.2% and palmitoleic acid by 57.9%. Linoleic acid also peaked in 2018, 35.3% above the minimum recorded in 2005, the coldest year in the series.
The statistical analysis reinforces the reading: the MUFA/PUFA ratio (monounsaturated versus polyunsaturated) showed a strong negative correlation with both mean annual temperature (r = −0.643) and maximum temperature (r = −0.725), while oleic and linoleic acids behave as communicating vessels (r = −0.850). The explanation is enzymatic: heat activates oleate desaturase and linoleate desaturase, which convert oleic acid into linoleic acid.
One particularly telling figure is the evolution of the linoleic/linolenic ratio by period: 8.37 in 1993-2000, 9.99 in 2001-2010 and 10.16 in 2011-2019. A sustained drift, not a one-off harvest anomaly.
An important qualification is in order: all the oils complied with the limits set by Regulation (EU) 2022/2104, with a single exception — the eicosenoic acid content in 1995, a year that was, incidentally, cold and very wet. The regulatory risk is not a present-day one; it is prospective.
Olive oil does not behave like oilseeds
The authors highlight a contrast of real relevance to the sector: in sunflower, maize and soybean, high temperatures during fruit development are associated with higher oleic acid content — precisely the opposite of what is observed in olive. The explanation points to the tissue in which the oil accumulates: the mesocarp in the olive fruit, as against the embryo or endosperm in oilseeds.
The isotopic fingerprint: a tool for origin control under climate change
The study incorporates a second strand: stable isotope analysis (δ¹³C, δ¹⁸O and δ²H) of 252 Slovenian samples from the 2006-2008 and 2019 harvests, together with a comparison of 79 oils from the 2007 crop originating in Slovenia, Croatia, Italy, Spain and Montenegro.
The results are clear-cut. δ¹⁸O responds above all to the frequency of hot days (r = 0.922) and to relative humidity, while δ²H shows a very strong relationship with mean temperature (r² = 0.94), making it, in the authors' view, the most climate-sensitive of the three isotopes. δ¹³C, by contrast, proved largely insensitive to year-on-year meteorological variability (r² ≤ 0.11).
In the country-by-country comparison, the Spanish samples — from Jaén, Córdoba and Madrid — showed the highest values for all three isotopes, consistent with the highest mean temperatures and the lowest rainfall in the set analysed. Principal component analysis clearly separated the Spanish and Italian oils from those of the Balkan macro-region.
The practical reading is twofold. On the one hand, the isotopic fingerprint confirms its potential as a tool for traceability and for tackling fraud in a product that ranks among the most adulterated foods in the world. On the other, if that fingerprint shifts along with the climate, reference databases will need periodic updating if they are not to lose their discriminating power.
What this means for the sector
The authors themselves acknowledge the study's limitations: cultivar was not controlled as a factor — although Istrska belica, Leccino and Frantoio predominate in Istria — the isotopic measurements cover only four harvests, and geographical sampling is uneven across countries.
With those caveats, the underlying conclusion holds. IPCC projections point to less rainfall and higher temperatures across the entire Mediterranean basin. If the relationship demonstrated in Slovenia holds in the major producing areas of the south — which start from higher baseline temperatures — both the product specifications of PDOs and PGIs and the purity thresholds set by EU and IOC standards will need to be reviewed in the light of a shifting agronomic reality.
This is precisely the kind of debate — quality, authenticity, olive grove adaptation and health — that shapes the agenda of the Olive Oil World Congress (OOWC).
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