That bottle of extra virgin olive oil you take off the grocery store shelf may not be what you think it is.

Instead of being a greenish-gold, fruity, fresh oil made from olives, rich in antioxidants and delicious to drizzle over a beautiful caprese salad, more likely than not it is a blend of oils, some made from olives, and some not.

In fact, a recent study by UC Davis that tested a number of the best-selling olive oils in California, including Bertolli, Star, and Colavita, found that 69% of the extra virgin olive oil imported into the U.S. did not meet the standards for extra virgin.

“It’s a big hoax,” said Tom Mueller, who will be talking about the issue, and his new book, Extra Virginity: The Sublime and Scandalous World of Olive Oil, on Saturday from 2 to 6 pm at Amphora Nueva Berkeley Olive Oil Works on Domingo Avenue. “What’s written on the bottle does not guarantee what is inside.”

Mueller, who lives in a medieval stone farmhouse surrounded by olive groves in Liguria, Italy, stumbled into the murky world of blackmarket olive oil in 2007, when he agreed to write an article about oil for the New Yorker. What he found surprised him.

“I figure I am living in Italy,” said Mueller, 48. “I’ve been eating some good olive oil. Italy is the world center of olive oil. Surely it would be an easy, folksy story. I had no idea what I was getting into – the collusion, the crime, talking to investigative magistrates.”

The result of his research was Slippery Business, an article that shook up American palates by showing how many large companies pass off inferior oil as extra virgin olive oil. Since neither the FDA nor the Italian equivalent really regulate the market, unscrupulous producers have developed numerous ways to adulterate extra virgin olive oil, according to Mueller. They cut olive oil with hazelnut or sunflower oil. They take musty oil made from rotting olives, deodorize it to remove the bad smell, and then add a bit of extra virgin oil to make it smell authentic. Then they slap fancy labels on glass bottles and sell it as extra virgin olive oil.

Some of the worst oil goes into industrial food, said Mueller.

“There’s a river of rotten oil going into food service — restaurants hotels, schools, hospitals,” he said. “The big companies are selling things that are not even olive oil.”

Most of the olive oil stocked in a grocery store is not as bad as the industrial oils, said Mueller. But the UC Davis test showed that even though the supermarket oils were branded extra virgin, much of the time they were only of virgin quality. The only imported oil that passed the test was Kirkland’s Extra Virgin Olive Oil – which is from Costco.

A number of California olive oils also tested well, including McEvoy Ranch, Corto Oil, California Olive Ranch, or COR.

Mueller, who hopes his book will kickstart a consumer campaign to fight for enforceable standards for extra virgin olive oil, said one reason to care is that true good olive oil, besides tasting good, has numerous health benefits. Consumers often think they are getting those health benefits when they buy a bottle labeled extra virgin, but often they are not.

“It would be hard to find a single more healthful substance than olive oil,” said Mueller. “Science is just starting to understand its 200+ compounds that are antioxidant and anti-inflammatory.”

Mueller is holding a book signing at Amphora in Berkeley because it is a store dedicated to carrying only the best olive oils. In Extra Virginity, he discusses the store’s owners, Mike and Veronica Bradley, who run Veronica Foods, founded by Veronica’s grandfather in 1924. The Bradleys have scoured the world to find well-made and flavorful olive oil from places as diverse as Italy, Morocco, Tunisia, Turkey, Portugal and Syria, among others. The company imports more than one million gallons of premium olive oil from 70 producers in 20 countries, according to Mueller. The Bradleys ship most of that to specialty stores around the country. Their only retail outlet is Amphora in Berkeley.

“They have been fighting against really sleazy merchandise for a long time in an industry that makes used-car dealers look transparent.”

Mueller’s readings at 3 pm and 5 pm will be accompanied by tastings of some of Amphora’s best olive oils.

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Olive oil in lieu of bicycles on Domingo Avenue [06.07.10]

Frances Dinkelspiel, Berkeleyside and CItyside co-founder, is a journalist and author. Her first book, Towers of Gold: How One Jewish Immigrant Named Isaias Hellman Created California, published in November...