The Tonka Bean: An Ingredient So Good It Has to Be Illegal

A wrinkled legume could be the next big thing—if only the FDA would stop busting chefs who crave its spicy, fruity aroma

Modern haute cuisine is working so hard to add scents to our plates: pillows of vaporized fresh-mown grass that vent at Grant Achatz's Alinea, bowls of smoke that seep at José Andrés's Minibar, hay brulée. With a flourish, the chefs at these restaurants call it "avant-garde cuisine"—drama and novelty are also very important. But according to the FDA, drama can sometimes be deadly.

Enter the tonka bean, a flat, wrinkled legume from South America with an outsize flavor that the federal government has declared illegal. Nonetheless, it proliferates on elite American menus. The tiniest shavings erupt in a Broceliande of transporting, mystical aromas.

The taste of the tonka bean is linked strongly to its scent. "Scents," I should say, as the tonka bean has many at once. I register the aromas of vanilla, cherry, almond, and something spicy—a bit like cinnamon. When served cold—say, in tonka bean ice cream—the taste is like a vanilla caramel with dark honey. When warm, perhaps shaved over scallops, it moves toward spiced vanilla. Additionally, the aroma of the tonka bean shavings (it's almost always shaved) is so affecting that it seems like an actual taste in the way that opium, which has no taste in the traditional sense, "tastes" like its rich, flowery smoke.

The French have had "fièvre tonka" ("tonka fever")—an overused food-mag pun on fève, the French word for "bean"— for years. The French version of Saveurmagazine features recipes that call for the tonka bean without fanfare. But in the United States it's a different story. Here, all foods that contain the chemical compound coumarin are considered by the FDA to be "adulterated" and have technically been illegal since 1954. Tonka beans are a major source of coumarin.

Before the law, refined coumarin was commonly added to commercial foods like cream soda, and used in synthetic vanillin. Extreme concentrations caused liver problems in rats (how unappetizing), and a rather overreaching ban on even natural sources of the compound was put in place. Coumarin has since been found to occur naturally in cinnamon, lavender, licorice, and a host of other commonly eaten plants—all of which would seem to be illegal under the regulation. Coumarin also accounts for the particular smell of fresh-cut grass and of fresh-dried hay (both in Alinea's grass-gas scent-pillows, and on your front lawn).

The fear of coumarin in the U.S. stems from the oft-repeated saw that it is a blood thinner. It's not. Coumadin® is the blood thinner trademarked by Bristol-Meyers Squibb. To make matters more confusing, Coumadin is made, in part, by changing the chemical structure of coumarin. Doctors who spoke with me (and who were terrified of being quoted) said there they're aware of no anti-coagulant effect from naturally occurring coumarin in general, or tonka beans in particular. In nature, only certain rare decomposition fungi can convert coumarin to the anti-coagulant molecule. Cows grazing on (pounds of) such rotting sweet clover led to the discovery of the Coumadin drug.

Humans would need to eat an unreasonably bovine amount of tonka bean to fall ill. The shavings of a single bean is enough for 80 plates. At least 30 entire tonka beans (250 servings, or 1 gram of coumarin total) would need to be eaten to approach levels reported as toxic—about the same volume at which nutmeg and other everyday spices are toxic.

So is the FDA enforcing this old law? Has anyone been busted for tonka bean possession? Yes! While the financial industry recently spun out of deregulated control, federal regulators got busy tracking down chefs using the tonka bean. An early bust, in 2006, was at Chicago's Alinea, currently the top U.S. restaurant in the San Pellegrino rankings, and a probable recipient of three Michelin stars in 2011. Chef Grant Achatz described the warning call from his supplier: "They said, 'Don't be surprised if the FDA shows up soon.'" His face still shows disbelief as he relates the story. "Two days later, they walked in: Can we look at your spice cabinet?"

But enforcement is clearly imperfect. Last month, I was able, after a dozen attempts at various merchants, to purchase tonka beans from a Seattle-based supplier on the Internet. The spice arrived in a plain yellow envelope, and made an excellent enhancement to my mother's Winesap apple tart recipe.

Ike DeLorenzo

A clever dessert leveraging the temperature-sensitive taste of the tonka bean is "Le Gâteau" created by chef Gabriel Bremer at Salts, in Cambridge, Massachusetts: a block of warm chocolate-tonka layered cake, semi-dried cherries, and light tonka bean ice cream. The fruit underscores the tonka bean's cherry notes, and accompanying smoked honey amplifies its spice. Brilliantly, the dish contains no vanilla, so the unique vanilla-like scent of the bean can reign on its own.

This is the kind of culinary innovation and taste experience we are missing when tonka is excluded from menus, and even products. The age-old and fortunately undisclosed recipes of various imported Italian amaro liqueurs probably also use tonka bean. They could meet the same fate as Poland's luxury Żubrówka vodka, flavored and colored by Polish bison grass for the rest of the countries in the world, but switched to use artificial flavors and colors for the United States market. Buffalo grass is unfamiliar to us and—you guessed it—contains coumarin.

A scientific re-evaluation of this old law, and its 1950s research, seems to be in order so we can catch up with the rest of the world. My tonka version of my mom's apple tart might, for the first time, outshine her original this Thanksgiving. That should not be illegal.