UC Davis: The Olive Oil Fridge Test Doesn’t Work
The “fridge test” does not tell you whether your extra virgin olive oil is real, the UC Davis Olive Center said this week after putting it through a lab trial. The test went viral after a television doctor recommended it last month. Here is what Davis did, what the oils actually did in the cold, and what works better when you are standing in front of the shelf.
Where the fridge test came from
On an episode of The Dr. Oz Show that aired on February 11, Dr. Mehmet Oz told viewers that more than two-thirds of the extra virgin olive oil sold is not pure extra virgin. His suggestion was simple: put the bottle in the refrigerator, and if it solidifies you can be “pretty sure it’s pure”, though he added that the method was not 100 percent foolproof.
The result was a wave of worried shoppers. Olive Center director Dan Flynn, who had appeared on the show, said his office, supermarkets and producers were flooded with calls and emails from viewers whose oil had stayed liquid. Research director Selina Wang proposed testing the method properly.
What UC Davis found
The team placed seven oils in a laboratory refrigerator set to 4.7°C (40.5°F) and checked them for up to 180 hours, seven and a half days. The report, “Refrigeration is not reliable in detecting olive oil adulteration”, by Xueqi Li, Selina Wang and Dan Flynn, was released on March 12.
| Sample | After 180 hours |
|---|---|
| Extra virgin, high quality | Some congealing at the bottom, never solid |
| Extra virgin, low quality | Some congealing, never solid |
| Extra virgin mixed 50/50 with lower-grade olive oil | Some congealing, never solid |
| “Olive oil” (virgin and refined blend) | Liquid |
| Refined canola, refined safflower, and a 50/50 olive oil and canola blend | Liquid |
Nothing changed in the first 60 hours. By five days the three samples with at least half virgin olive oil showed a little congealing at the bottom of the bottle, but none of them ever fully set. The telling result is the blend: an extra virgin cut half and half with a lower grade behaved just like the genuine extra virgin, so it would “pass” the fridge test while not being pure extra virgin at all. And the high-quality and low-quality extra virgin oils behaved the same, so the test says nothing about quality either.
The reason is chemistry. Waxes and certain long-chain fats make olive oil cloud and thicken in the cold, but the amounts vary from oil to oil. Before the Davis report, Australian taster Richard Gawel had called the test a myth, and the North American Olive Oil Association, the importers’ group, called it “completely false and misleading”.
What to do instead
- Look for a harvest date and buy within about 15 months of it. A best-before date is not the same thing.
- Prefer dark glass or tins, and keep the oil away from light and heat at home.
- Look for a certification seal that involves both a chemical analysis and a tasting panel. Flynn pointed to the Australian and Californian programs.
- Taste it. Fresh extra virgin should smell of fruit and green things, with some bitterness or pepper. Flat, greasy or crayon-like means old or poor oil.
Plenty of genuine oils are filtered hard or chilled at the packing plant precisely so they stay bright in the bottle and do not cloud on a cold shelf, because customers return cloudy oil thinking it has gone off. So a perfectly honest extra virgin can sail through your refrigerator without a hint of solidifying, while a blend with enough virgin oil in it can thicken nicely. The cold tells you about waxes, not about honesty.
Sources
- UC Davis Olive Center: Refrigeration is not reliable in detecting olive oil adulteration (March 2013)
- Olive Oil Times: Davis Researchers Put Olive Oil ‘Fridge Test’ to the Test (March 12, 2013)