Most people know what to expect from olive oil: a pleasant green tint, a faint aroma, a touch of bitterness. Upon advice from health experts who tout its cholesterol-lowering powers, many of us prefer it over its pale yellow, flavorless cousins.

Some years ago, I too gave over to the better taste and better qualities of olive oil for most everything. Here and there, by happy accident, I even had oil with an unusual pungency and stout scent, usually delivered for bread-dipping at a nice restaurant. I never gave it much thought.

Recently, however, I heard an NPR interview with Tom Mueller, whose book Extra Virginity tells tales wondrous and sordid about the slippery world of olive oil. In the book, Mueller explores the oil’s long history as a food substance, fuel, perfume base, and fodder for slathering with abandon upon one’s body. (He tells tales of ancient Greece, where bathers and athletes used so much perfumed oil that a side industry sprouted to sell the oil they subsequently squeegeed from their skin.)

He also explores the surprisingly shady world of olive oil production, one which has grown more complex—and exploitable—as the oil’s popularity has increased dramatically worldwide.

Mueller, in between waxing eloquent about the near-sacred status of olive oil and its longstanding reign as an extraordinarily versatile substance, basically shatters an illusion in which many of us have been ensnared for years. Go to the grocery store and grab a bottle of “extra virgin olive oil,” he says, and chances are you’re getting something that is quite far from the liquid that goes by the same name in the countries that are oft-touted on those bottles on the grocery shelf. It may not even be 100 percent olive oil.

It’s tempting to think that’s no big deal. Turns out it’s a very big deal.

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In seeking the real thing, olive oil that meets the legal definition of extra virgin olive oil (Europe has long had exacting standards, but new USDA definitions are voluntary), I sought the advice of Mary Lou and Bob Heiss, owners of Northampton’s Cooks Shop Here, which specializes in tea, coffee, spices and olive oils, among other imported treats. The Heisses don’t just sell their treats—they travel to the sources, find the small operations and the farmers who produce the goods and work directly with them.

They sat me down in front of three bowls of nearly luminescent green oil. The tastes that greeted me via small pieces of bread soaked in oil were eye-opening: astringent, peppery, bright, smooth. The difference in taste between these and more commonplace oils was readily apparent. But was I willing to pay a lot more for these clearly superior tastes? Would the difference matter once the oil was merely part of a dish instead of the main attraction?

I turned my attention to the last bowl. This one was called Siciliani, intriguing for its luminous opacity. It’s a “novello,” an oil that hasn’t been left to age and mellow. I dipped the bread, gathering a generous serving to really taste the oil. Very bright, distinctly and boldly fruity, though I didn’t have a ready arsenal of terms for what I tasted beyond those general impressions. A hint of bitter bite, not at all unpleasant, lurked too.

I swallowed appreciatively. Suddenly the back of my throat was assaulted with a peppery burn, as if horseradish had missed its usual top of the palate mark. My eyes watered so severely I nearly had to grip the chair. What on earth was this about?

I tried it again, and, once the burn was expected, the experience was as enjoyable as a dose of wasabi.

Mary Lou Heiss asked me, “Did you get the burn at the back of the throat?”

She explained that what I was experiencing was the burn created by some of the most healthful stuff in olive oil. In Exra Virginity, Mueller relates the story of a scientist who tasted that burn and, relating it to the taste of ibuprofen he’d experienced, set out to isolate the burn. The result was dubbed “oleocanthal.” This substance, along with hundreds of polyphenols, hydrocarbons and vitamins that give oil its healthy punch, “vanish[es] when the oil is treated with chemicals or heat.” That is, of course, precisely what happens with much of the oil that makes it to shelves.

The scientist in question, Gary Beauchamp, says, “I used to buy any old oil in the supermarket. … Today, knowing what I know, I’m willing to spend $25 or more for a bottle of high-quality oil.”

Europeans who know their oil feel the same way, and Mueller talked to more than one official who wished a major health scandal involving olive oil would surface to bring sufficient awareness to force changes in an industry that brings plenty of stock to our shelves, but stock that may or may not offer the benefits we seek. He says such a scandal came and went 30 years ago, when fake olive oil made with denatured rapeseed oil killed 800 and sickened some 20,000 in Spain. Though that’s clearly a unique extreme, Mueller says that (even, apparently, in Europe) olive oil is “a business where opaque and misleading labelling is the order of the day.”

It’s yet another maddening example of the difficulty of obtaining real food in a system that values quantity, replicability and homeogeneity. It’s impossible not to wonder how many other instances of adulteration and mislabelling fill our shelves, and how many advanced degrees are necessary to simply buy groceries that deliver what their packages purport to.

The mislabelling and misleading, contends Mary Lou Heiss, is partly because of two things that Americans value highly: bargains and a “safe” homegeneity of product. Since the dawning of the age of fast food some half-century ago, she says, “We’ve seen the rise of the belief that food should be cheap. It’s part of the American psyche to hunt for the good deal.”

So what do you do? One answer is obvious: ante up for extra virgin olive oil that meets the legal definition. It’s highly unlikely to be found at big supermarkets. Look closely at labels, and you can find it, even if it’s uncommon. The real McCoy will make mention of some of the defining characteristics of extra virgin: produced solely from olives, and solely by mechanical means.

Mary Lou Heiss says another good indicator is that it bears a place name that’s a real place rather a company name. Usually, she says, labels on inferior oil bear a list of source countries for the olives (even if the front says “product of Italy”). That means the producer has shipped in truckfuls of olives to make the oil, a sure sign of “commodity” oil. The real thing, made by small producers, is picked and very quickly turned into oil, not shipped.

“That speeds makes the difference,” says Mary Lou Heiss. “The oleic acid in the olive is stable, but once it’s picked, the clock’s running.” Twelve hours, she says, is the gold standard in terms of preserving the highest amount of the good stuff within.

Of course, not everyone has $25 to spend on oil, health benefits or no. There seems to be no easy answer to that issue. Bob Heiss says his best suggestion is to get real extra virgin olive oil, but supplement it with other things, like good brands of peanut or canola oil, or even butter.

In order to avoid getting olive oil that’s got little or none of its healthy qualities left, he says a couple of rules help. “Avoid anything in a really big container,” he says, adding that real olive oil is simply expensive to produce; price is, unfortunately, a good indicator. “If something seems too good to be true, it probably is,” he adds.

The oils you’ll find at Cooks Shop Here and other retailers who don’t deal in bulk are, truly, a world apart in taste. In fact, says Mary Lou Heiss, it can be a challenge for newcomers to their store to understand that the tastes they’ll encounter are “bigger and bolder.”

Once you get over the shock of just how big those tastes can be, however, chances are you’ll come back for more. Even if it’s a little at a time.