Since ancient times, olive oil has held an almost mythical status; it was considered to be not just an essential culinary adornment, but a contraceptive, detergent, pesticide and perfume. Today, its following remains cult-like, with devotees wed to tasting rituals, such as only tasting it in special glass containers at 28 degrees Celsius, and touting obscure bits of knowledge about the numerous olive oil varietals, from Albatro to Salicino, from which it is pressed. Throw in its additional health benefits, and sales of olive oil have doubled in the past two decades, according to International Olive Council figures.

But, as with all good things, retaining its high quality and purity has become a bone of contention, especially when it comes to labeling olive oil as "extra virgin."

A book published earlier this month "Extra Virginity: The Sublime and Scandalous World of Olive Oil" by Tom Mueller (Atlantic Books in the U.K.) explores the wide-scale adulteration of the product. Mr. Mueller, an American writer who lives in the northwestern Italian province of Liguria, first exposed the scandals surrounding the fraudulent production of olive oil in an essay published in the New Yorker in 2007. This included the blending of cheaper vegetable oils such as sunflower or hazelnut and then selling it as extra virgin olive oil, or deodorizing lower-grade olive oil to remove noxious flavors. Another scam was the importation of inferior olive oils into Italy and then selling them as if this was the country of origin.

Olives harvested for olive oil in Dolcedo, Italy.

This book expands the scope of his earlier work and makes unsettling reading for anyone who imagines that what they purchase in many supermarkets is actually high-quality olive oil, with all of its attendant life-enhancing attributes.

"The olive oil stocked on the shelves of the average supermarket is of a very, very low standard and most are flawed in one way or another," Mr. Mueller said in an interview earlier this week. He also believes the description of olive oil as "extra virgin" is a virtually meaningless phrase.

"According to the letter of the law—as drawn up by the U.S. [Department of Agriculture], the Australian government and an intergovernmental organization called the International Olive Council—the category 'extra virgin' olive oil is quite a low bar. The definition is that the oil must meet several basic chemical parameters, have some flavor or aroma of olives and cannot have any sensory flaws," he says. "This really doesn't say much about its quality, only that it cannot be bad. It is a bit like selling First Growth Bordeaux and cartons of nondescript stuff both under the category of fine wine."

The argument is that poor-quality, low-priced olive oils are driving the genuine high-quality producers out of business, as it is possible to purchase liter bottles of "Extra Virgin" olive oil in British supermarkets for less than £5.

Due to the labor-intensive practices of small-scale olive-oil producers in hilly regions like Tuscany, it would be a struggle for them to sell their handcrafted product for less than three or four times this amount, Mr. Mueller contends. These are the producers who create the intensely flavored, peppery oil that is used in the best restaurants or sold in small delicatessens and grocery stores.

Each autumn, London's River Café co-founder Ruth Rogers takes most of the kitchen staff to tour the leading producers in northern Italy to assess the olive oil vintage, which can vary as much as those of wines. Certain oils that catch the attention of the staff are bottled under the restaurant's private label, which includes harvest details.

Just last month, both kitchen and front-of-house staff tasted about a dozen oils to choose a handful River Café would use. A week later, I went there for lunch. Sian Owen, River Café's head chef, explained that the meal I was served used at least four different oils, depending on the dish. "The oil on the bruschetta was Selvapiana from Chianti Rufina in northern Tuscany, which is more robust to withstand the grill flavors. On the finely chopped raw veal dish plus the freshly grilled langoustines, we used Capenzzana oil, which is closer to Florence as it is a very beautiful delicate oil. With the wood-roasted turbot, I put on the I Canonici oil from the Fontodi estate in Chianti Classico, as its peppery, green flavors work best with fish."

Despite his criticism of the industry, Mr. Mueller isn't pessimistic about the future. "I have a sense of optimism because consumers are finally beginning to ask the right questions, like who is making this, how fresh is it, why isn't there a harvest date on this, what is rancidity, why are bitter and pungent flavors good? However, when it comes to enforcement of the regulations, I am less bullish—what is going to happen in southern Italy and Spain when the European Union agricultural subsidies fall off in 2013? This is serious stuff and it is going to get worse. In the European Union, the influence from above is largely negative—they merely wish to promote olive oil consumption but they don't celebrate quality."

The International Olive Council didn't respond to requests for comment.

Says Mr. Mueller: "I think in this case, the consumer is going to force the issue by saying 'I want an early harvest Picual variety,' or asking their supermarket 'why are you selling me this olive oil which smells bad?' It is a similar process to the way that wine drinkers, lovers of artisanal cheese and coffee have improved quality through their knowledge and demands."

Write to Bruce Palling at