The report, released Wednesday by the University of California-Davis Olive Center and the Australian Oils Research Laboratory, is a follow-up to a similar study the two research centers conducted last summer. That earlier report said that two-thirds of common brands of extra-virgin olive oil found in California grocery stores aren't what they claim to be. Many of those problematic oils, labeled "extra-virgin," were imports that commanded premium prices, according to the researchers.
Wednesday's report, entitled "Evaluation of Extra-Virgin Olive Oil Sold in California," drew a larger group of samples from fewer brands. That was done in part to address some of the criticisms from foreign producers about the research methods used in last year's report. Ninety-nine percent of the olive oil consumed in the U.S. is imported.
The brands tested for the most recent report were Filippo Berio, Bertolli, Pompeian, Colavita and Star. The researchers also tested samples of Lucini, the top-selling premium Italian brand; Cobram Estate, the largest Australian olive oil producer; and California Olive Ranch, the leading U.S. producer.
California Olive Ranch, headquartered in Oroville, Calif., helped fund the research.
For the latest study, UC Davis researchers said they went to retailers in Northern, Central and Southern California in September and October and bought bottles labeled 100 percent extra-virgin olive oil from domestic and imported producers. They then subjected the oils to sensory and chemical tests.
According to the report, researchers found that 73 percent of the 134 samples from the eight producers failed the sensory, or taste and smell, tests established by the International Olive Council, which is based in Madrid.
In addition, the report said, the imported and domestic samples were run through seven chemical laboratory tests. Seventy percent of the imports failed one particular test; 50 percent failed another test. Some of the samples failed five of the seven chemical laboratory tests.
Researchers said only 11 percent of the California-produced samples failed one test. The rest of those samples passed all of the chemical tests, as well as the sensory tests.
"This confirms what we found in the first report. Now, there are two reports and quite a bit of consistency," said Dan Flynn, executive director of the UC Davis Olive Center.
The International Olive Council, whose members account for 97 percent of the global production of olive oil, was less convinced. In a statement released Wednesday, the organization said both reports had "the same evident undercurrent of aggressive, inexplicable criticism of imported olive oil quality."
Industry officials generally agree that the "extra-virgin" designation is proper for oil that is cold-processed to prevent degradation of aromatic compounds and has higher levels of healthful fats and antioxidants. It also has relatively low acidity levels.
Purity is a serious concern for some consumers. Some state agencies previously have uncovered oils labeled 100 percent extra-virgin olive oil that were blended with cheaper canola, seed or nut oils -- a significant health threat to people with allergies. No such mixing of seed oils was found in last year's tests or the recent tests of products sold in California, according to the report.
Money is also at stake, as extra-virgin oil is often sold as a premium-priced product.
Yet consistently replicating the researchers' findings has proved challenging to a California legal team that led a class-action lawsuit over the purity of imported olive oil.
Last August, a group of chefs, restaurants and others filed a complaint in Orange County Superior Court claiming that several retailers and olive oil producers had misled Californians about the quality of the olive oil they sold.
But plaintiff attorney Daniel J. Callahan said his firm ran into difficulties when it sent olive oil samples to various laboratories for testing: The results, he said, were inconsistent.
"There were good grades in Georgia, but bad in California," Callahan said Wednesday. "It wasn't consistent enough to meet the profile of the kind of case" his firm handles.
The class-action complaint was dropped last month, Callahan said.
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