The mystery of Quorn begins before the first bite.

You approach the food with suspicion, pick up a single tan-colored morsel, roll it between your digits to test its texture, perhaps sniff it a bit to see if it reminds you of anything you've eaten before ... and then, if you're brave, you might decide to cautiously put in your mouth.

There's a pleasant surprise, then, because Quorn tastes just like chicken. Or, depending on the kind of Quorn you're trying, it might taste just like beef. Either way, it's pretty good.

But Quorn is not chicken or beef, and even though it's pronounced KWORN, it doesn't have anything to do with corn. The meat substitute -- which has been popular in Europe for more than a decade and is now on the market in the United States -- is instead made from a substance called mycoprotein, which Marlow Foods, Quorn's manufacturer, says is one of the most nutritious and tasty foods ever discovered.

But this is where Quorn's mystery deepens. What is mycoprotein? According to Quorn's packaging, mycoprotein is "mushroom in origin." But the stuff is not mushroom at all: Instead, it is "the processed cellular mass that is obtained from the filamentous fungus Fusarium venenatum strain PTA-2684," according to Marlow's application to the U.S. Food and Drug Administration for sale in America.

In other words, Quorn is a kind of fungus, and it's not at all a kind of mushroom. That doesn't mean there's anything wrong with it. Indeed, the FDA thought well enough of the fungus to approve late last year, admitting it into a class of foods "generally recognized as safe."

But some scientists are concerned that mycoprotein was not adequately tested, and that it could cause a host of allergic reactions in the population if it becomes popular. More than that, some nutritionists and Quorn's competitors say that at the very least Marlow Foods should tell consumers what Quorn really is -- it's deceptive, they say, to carry on like it's a mushroom when it's actually something else.

Mycoprotein was discovered in the 1960s, at a time when nutritionists believed -- erroneously, it turned out -- that humans were on the brink of a worldwide protein shortage. The tiny organism was found in the soil in the village of Marlow, England, and though nutritionists found its properties intriguing, it took them some time to figure out how to mass-produce it.

"After research, it was found that the most successful way of growing mycoprotein was by fermentation, similar to the process used when making products such as yogurt," the company says on its website. "When it is harvested, mycoprotein has a similar appearance to bread dough, and is composed of a mass of very fine fibers. Because of the similarity between mycoprotein and meat fibers, Quorn products have a texture similar to that of lean meat, although non-animal in nature."

Like other meat substitutes -- many of them made from soy -- Quorn is much healthier than meat, as it is low in fat and high in non-animal protein and fiber. Also, the company says that it takes about five times less energy to produce a gram of Quorn than it does a gram of meat, and factory-based Quorn production is even more ecologically friendly than growing huge fields of soybeans.

But the best thing about Quorn is that "it has a really fabulous bite," said David Wilson, Quorn's U.S. vice president. He means that it has the firmness of meat -- when you chew into a nugget of Quorn, it pushes back against your teeth a little, like beef and chicken do. Soy products are generally softer, requiring less effort to chew.

All that is well and good, said Michael Jacobson, the executive director of the Center for Science in the Public Interest, but people would be a lot less receptive to Quorn if they know what it is: a fungus that comes from the ground, an organism that's "grown in big vats in England."

"They're trying to trick people that it's mushrooms," Jacobson said, explaining his beef with Quorn. While all mushrooms are fungi, not all fungi are mushrooms, and many of them are very different from your standard salad-caliber 'shroom. Calling Quorn "mushroom in origin," then, is a bit like saying that beef is chicken in origin, or that ice cream is a kind of grass.

"The fungus family is an enormous family, and one expert told us that this is as distantly related to common mushrooms as a jellyfish is to a human being," Jacobson said.

That's why Jacobson has petitioned the FDA (PDF) to require that Quorn products not say "mushroom in origin" and instead state that mycoprotein is a "fungus." Gardenburger, the manufacturers of one of the country's most popular meat-free patties, have filed a similar claim (PDF), as have some mushroom growers and processors.

Wendy Preiser, Gardenburger's vice president for marketing, said that her company is afraid that Quorn's labels will cause people to be suspicious about all meat-free products. She pointed to a survey Gardenburger commissioned, which found that most people -- six in 10 -- thought that "mushroom in origin" meant that the product had actual mushrooms in it. When they were told it was "fungus," half as many people were willing to try it, she said.

In addition to his concerns about the labeling, CSPI's Jacobson is also worried about the safety of Quorn. The FDA did not perform its own tests on the food, and it instead relied upon Marlow's tests of mycoprotein.

Jacobson thinks these tests were not comprehensive, especially since he says that he has found at least 10 documented cases of adverse reactions caused by mycoprotein, and more are coming in to a website his group set up to collect complaints.

Without any publicity for this site, half a dozen complaints have trickled in, which leads Jacobson to believe that many more people are suffering from Quorn-related problems.

But Marlow is adamant that its products are safe. Wilson, the company's U.S. rep, said that numerous studies have been done, and all of the data has been shared with the FDA and international regulatory agencies. Moreover, he said, this year the company is set to sell its billionth portion of Quorn, and in that time it has received a relatively small number of complaints.

One person in 146,000 will have an adverse reaction to Quorn, Wilson said. That's a smaller rate than soy -- which Wilson said was around one in 350. Wilson also dismissed Gardenburger's complaints, saying that they had an obvious interest in seeing Quorn suffer.

Wilson sent Wired News a big variety of Quorn chicken-style products last week -- nuggets and patties (which are breaded), tenders (unbreaded, for use in cooked meals like stir-fries and fajitas) and a serving of Quorny fettuccine Alfredo.

For about an hour on Thursday, the office went a bit Quorn crazy, with 10 or so people popping into the coffee bar to taste this advanced food. The feedback was mostly positive. Everyone liked it, and some people said they loved it. Several said that the nuggets were indistinguishable from chicken, and others said that while they could taste a difference, they thought Quorn was very similar to meat.

But Wired News's acerbic copy chief, a man who seems to know his way around a slab of steak, said that the nuggets weren't "chicken-y" at all -- bizarrely and cryptically, he said that they tasted like "some sort of hors d'oeuvres."

One copy editor said she thought Quorn had succeeded beautifully in creating something that tastes exactly like chicken, but she added that it was the type of chicken that McDonalds serves, a greasy, fast-food sort -- which is an achievement something on the order of creating a perfect imitation of a Thomas Kinkade painting. Sure you can do it, but why?

Only one person -- a reporter -- reported any adverse reactions. It wasn't a physical thing, she said, but rather a "negative aftertaste. Recollections of the nugget sort of remained in my digestive memory throughout the day, and it required the consumption of a very garlicky pizza for dinner to exorcise it."

Others were kinder, and after they tasted it, many said it didn't bother them so much that Quorn is actually a mysterious fungus.

Perhaps that's because the whole business of phony food depends on deception; to really enjoy fake meat, you might have to forget, if only for a moment, the true origins of the stuff you're biting into. On the bright side, at least it's not the flesh of some poor cow.