Tonka beans: Delicious, sought-after, and potentially deadly in large doses

The scent of Tonka beans has been described as a multi-layered sensation embracing notes of vanilla, almond, honey, caramel, cinnamon and cloves.
The scent of Tonka beans has been described as a multi-layered sensation embracing notes of vanilla, almond, honey, caramel, cinnamon and cloves.PHOTO: WIKIMEDIA COMMONS

Gourmet restaurants might not seem to be a natural candidate for drug raids.

But one ingredient, which appears regularly on the menus of fancy eateries across the United States, has been targeted by law enforcement: the humble tonka bean.

This wrinkly black seed, from a tall tree native to Central America, is much coveted for its fragrance, which has been described as a multi-layered sensation embracing notes of vanilla, almond, honey, caramel, cinnamon and cloves.

In fact, tonka bean has been used as an additive to boost vanilla bean flavours in all sorts of products.

In Michelin-starred restaurants, it is shaved in tiny slivers over desserts to lend a heady fragrance to sweets.

Tthis delicious ingredient is also officially banned for consumption in the United States, although it is used in perfumes soaps and candles.

The reason for the consumption ban: the bean contains high levels of a chemical called coumarin. This chemical was first isolated from tonka beans in 1820 , and studies have shown that it causes damage to the liver and could cause death. For example, 5g of coumarin could kill a sheep.

Coumarin also occurs naturally in cinnamon, lavender, liquorice, cassia and even grass. But the tonka bean contains very high levels of coumarin.

As a result, the US outlawed the ingredient for food, and even the European Union has set limits for safe daily doses of the chemical.

But connoisseurs of flavour are not discouraged by the science or the law. Thomas Raquel, head pastry chef at Michelin-starred Le Bernardin in New York, told the BBC: "As long as you don't use a copious amount of it - obviously a copious amount could cause death - it really is delicious."

In spite of government crackdowns on restaurants, Paul Liebrandt, former co-owner of the Corton in New York, told the BBC: "Let's just say I know where to get them, it's not a problem to get them."

For gourmands, the data should be reassuring enough. A single bean contains enough shavings for 80 plates of food, according to The Atlantic, and you need to eat at least 30 tonka beans (or 250 servings, with 1 gram of courmarin) for ill effects to kick in.

Then again, the tonka bean is hardly the most dangerous ingredient in the world.

Just for a little perspective, a single pufferfish, prized by the Japanese as a delicacy, contains enough poison to kill 30 people. Just one milligram of the fugu's deadly tetrodotoxin can kill a man.

In this case, one man's meat really is another man's poison.