Many of the olive oils lining supermarket shelves in the United States are not the top-grade extra-virgin oils their labels proclaim, according to a report from the University of California, Davis.
Researchers analyzed popular brands and found 69 percent of imported oils and ten percent of domestic oils sampled did not meet the international standards that define the pure, cold-pressed, top-quality olive oils.
"Consumers, retailers and regulators should really start asking questions," said Dan Flynn, executive director of UC Davis' Olive Oil Center, which conducted the study in partnership with the Australian Oils Research Laboratory, in South Wales.
Funding for the study came in part from California olive oil producers and the California Olive Oil Council, a trade group that works to promote locally produced oils.
Although the survey's sample size was relatively small and selected at random -- 19 widely distributed brands purchased from retailers in San Francisco Bay Area, Sacramento and Los Angeles -- the study held the claims on their labels to a scientifically verifiable standard, said Flynn.
The results came as the U.S. Department of Agriculture prepares to adopted scientifically verifiable standards for nomenclature such as "virgin" or "extra virgin," in an effort to clear up concerns about labeling accuracy. The standards were adopted in April, and will be implemented in October.
The U.S. is the world's third largest consumer of olive oil.
The North American Olive Oil Association, which represents most olive oil importers, has conducted its own tests for years on the products it imports, and found problems with only one percent of samples, said its president, Bob Bauer.
Bauer also noted the study's funding, which came from industry groups.
"The research was done by academics, but with funds supplied by the industry," Bauer said. "When you look at results that are so different from ours, it does raise some questions."
The head of the Olive Oil Chemistry and Standardization Unit at the International Olive Council, based in Spain, was not available for comment.
There have long been questions about the quality of some of the olive oil being sold as extra virgin, said Flynn.
Olive oil production is labor intensive and costly. Poor quality oils can be made from olives that are too ripe or damaged.
Extra virgin olive oil is also fragile -- it is susceptible to oxidation and degradation of its aromatic compounds due to aging, or to exposure to high temperatures and light.
The delicate nature of the production has led to adulteration, where extra virgin olive oil was blended with cheaper, refined olive oil, or with seed or nut oils.
The discovery of altered oils in the 1990s led the European Union, which produces much of the world's supply, to create an investigative task force to look into the matter.
The results of the survey weren't surprising to Ruth Mercurio, who owns and runs We Olive, a California chain of stores specializing in olive oil.
"It's sad for consumers that there is fraud out there," said Mercurio, who has trained in-house tasters to help verify the quality of their product. "It's a problem, and maybe this will get folks to perk up and listen."