How a University Changed American Olive Oil
It began with a nuisance: thousands of campus olive trees dropping fruit on the pavements. It ended with a research centre whose testing of supermarket oil caused one of the biggest rows the industry has had — and the argument is not finished.
Universities in olive-growing regions usually keep olive trees for shade and decoration, and the fruit is a nuisance — it drops, it stains paving, it gets walked into buildings. At the University of California, Davis, somebody eventually asked the obvious question: why are we sweeping this up instead of pressing it? The campus began producing its own oil, and in 2008 established a dedicated research centre. Two years later that centre published something that changed the conversation about olive oil in America.
The report that started the fight
In 2010, researchers tested supermarket samples of imported oil sold in California as extra virgin, applying both chemical analysis and the trained sensory panel that international standards require. The result was striking: around 69 per cent of the imported samples failed the sensory standard for extra virgin. A follow-up the next year, focused on top-selling imported brands, put the failure rate around 73 per cent.
Note carefully what failing means here. It does not mean the oil was fake, dangerous or adulterated with other oils. It means trained tasters detected defects — the fusty, musty, winey, rancid notes that indicate poor fruit, slow milling, bad storage or simple age — at levels that disqualify a sample from the top grade. In other words, the oil was frequently real olive oil that had ceased to be extra virgin somewhere between the mill and the shelf, while the label went on saying otherwise.
| Test | What it measures | What it catches | Limitation |
|---|---|---|---|
| Free acidity | Free fatty acids from breakdown of the oil | Poor fruit, delays, bad handling | Can be corrected by blending ; passes plenty of tired oil |
| Peroxide value | Early-stage oxidation | Oil starting to turn | Says nothing about flavour defects |
| UV absorbance | Refined oil markers and oxidation products | Some adulteration and refining | Sophisticated blending can dodge it |
| Sensory panel | Defects and fruitiness, judged by trained tasters | Fusty, musty, winey, rancid oil — the real-world failures | Human, contested, expensive, hard to standardise |
| DAGs and PPP | Degradation and refining markers | Age and refined-oil contamination | Not part of every regulatory standard |
The objection worth taking seriously
The importers pushed back hard, and it would be lazy to pretend their arguments were worthless. Two are worth stating plainly.
First, funding. The research was supported in part by Californian olive oil interests — producers who compete directly with imports. That does not make the results wrong, and the methods followed recognised international protocols, but it is exactly the sort of conflict a careful reader should register rather than wave away.
Second, the sensory panel itself. Grading olive oil partly by trained human tasters is genuinely unusual in food regulation and genuinely contested. Panels are trained and calibrated to international protocols, but they remain human, results can vary between panels, and the industry has argued for years about how much regulatory weight a taste test should carry. The counter-argument is simple and, I think, decisive: the defects that matter most to a consumer — rancidity, mustiness, the flat taste of old oil — are precisely the ones chemistry alone does not reliably catch.
| What the campus started with | Ornamental olive trees whose dropped fruit was a maintenance problem |
|---|---|
| Research centre established | 2008, at the University of California, Davis |
| First major report | 2010 — imported oils sold as extra virgin in California |
| Headline finding | Around 69% of imported samples failed the sensory standard |
| Follow-up, 2011 | Around 73% of samples from top-selling imported brands failed |
| What failure meant | Sensory defects disqualifying the sample from the extra virgin grade, not adulteration |
| Main criticism | Partial funding from Californian producers ; the contested status of sensory panels |
| Lasting effect | Harvest dates on labels, more testing, and a far more sceptical American buyer |
What actually changed
More than the industry likes to admit. American consumers learned that the words extra virgin describe a grade assessed at a moment in time, not a permanent property of the liquid — the single most useful thing anyone can know about buying olive oil, and the subject of extra virgin that is not. Retailers began asking suppliers harder questions. Producers who were doing things properly discovered that saying so was now worth money, and harvest dates started appearing on labels that had never carried them.
The Californian industry also, undeniably, benefited from the reputational damage to imports. Both things can be true at once: the research was in the interest of its funders and it told American shoppers something true and useful that nobody else was telling them.
What to do with this as a buyer
- Treat the grade as a claim about the past. It was assessed at bottling, not at purchase.
- Prefer a harvest date over a best-before date. Producers who print one are telling you something.
- Learn the defects. Fusty, musty, winey and rancid are recognisable once you have met them.
- Dark glass or tin, always. Most sensory failures are storage failures.
- Read who funded the study. Including this one. It is a good habit for any food research.
The UC Davis olive oil research: common questions
What did the 2010 UC Davis report find?
That around 69 per cent of imported oils sampled in California and sold as extra virgin failed the international sensory standard for that grade. A 2011 follow-up on top-selling brands found roughly 73 per cent failing.
Did that mean the oil was fake?
No. Failing the sensory standard means trained tasters detected defects such as fustiness, mustiness or rancidity. That usually indicates poor fruit, slow milling, bad storage or age — not adulteration with other oils.
Why was the report criticised?
Chiefly because it was funded in part by Californian producers who compete with imports, and because grading oil by trained human tasters is inherently contested. Both criticisms are reasonable to weigh.
Is a sensory panel a legitimate way to grade oil?
It is the international standard, and it catches the failures chemistry misses — rancid and musty oil can pass chemical tests comfortably. It is also human, variable and expensive, which is why the argument persists.
What changed as a result?
Greater scepticism among buyers, more testing by retailers, and the spread of harvest dates on labels. It also boosted the Californian industry, which was among the funders.
The number everybody quotes from that report is 69 per cent, and it gets repeated as though most imported olive oil were counterfeit. It was not. Overwhelmingly it was real olive oil that had gone tired — picked late, milled slowly, shipped warm, stored bright, sold old. That is a less thrilling scandal but a far more useful one, because it is fixable and because it puts the power back in your hands. Buy recent, buy dark, buy small, finish it. Nobody can sell you a defective oil if you can taste the difference.
Drawn from the University of California, Davis Olive Center reports of 2010 and 2011 on extra virgin olive oil sold in California, and International Olive Council grading standards including sensory assessment.