Popular olive oil brands are under investigation for trying to pass off inferior olive oil for extra virgin, according to London's Telegraph newspaper. The brands in question are all from Italy and include big names in the olive oil business like Bertolli, Santa Sabina and Primadonna.

Italian media first discovered the alleged fraud, the Telegraph reports, with a consumer protection organization later picking up the case. Of 20 brands tested in a laboratory, nine were said to contain lesser quality olive oil. The other brands named in the investigation are Antica Badia, Carapelli, Coricelli and Sasso.

"The damage caused by this deceit is enormous, not just for consumers but also for the entire country and for the image of products that are made in Italy," said Rosario Trefiletti, the president of Federconsumatori, a consumer association in Italy, which is the world's second biggest olive oil exporter behind Spain.

At least one of the companies named in the investigation has disputed the claim. 

"These analyses, although carried out by professional tasters, are now widely considered not sufficient to evaluate the quality of an olive oil," Coricelli said in a statement. 

Olive oil production is more or less a shady business. In Europe, olive oil is the most adulterated agricultural product, according to the Tom Mueller, author of the book "Extra Virginity: The Sublime and Scandalous World of Olive Oil." Producers often cut olive oil with cheaper oils like hazelnut and sunflower and still call it extra virgin, the highest quality.

But the problem isn't confined to Europe. "In America, olive-oil adulteration, sometimes with cut-rate soybean and seed oils, is widespread, but olive oil is not tested for by the F.D.A.—F.D.A. officials tell me their resources are far too limited, and the list of responsibilities far too long, to police the olive-oil trade," Mueller told The New Yorker in 2012.

Earlier this year, the National Consumers League, a nonprofit advocacy group, found that six of 11 bottles marked extra virgin olive oil were not, in fact, extra virgin. The organization didn't publish the names of the brands, but it did say they were sold at Whole Foods, Safeway, Trader Joe's and Giant.

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