Pop the red, cranberry-sized miracle fruit in your mouth and chew it for a while, allowing its juices to coat your mouth. It doesn't taste like much.
But what follows "is just a miracle or a kind of magic" according to Keiko Abe, of the University of Tokyo, as you sample other foods. "Beer tastes like sweet juice. Lemon tastes like sweet orange."
Sour foods are perceived as trippily sweet when tasted for up to an hour after consuming the berry. This effect has led curious folks in the U.S. and elsewhere to seek the miracle fruit for "flavor-tripping" parties : pop the fruit with friends, then sample a smorgasbord of sour-leaning snacks: limes, goat cheese, beer, grapefruit, vinegar, pickles and more.
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"To me it was very exhilarating. It really is a very joyous experience," said writer Adam Gollner of trying the fruit. Gollner is author of The Fruit Hunters, which includes a chapter on the miracle fruit. "It's almost like this thing that you can't understand that is happening to you. That sense of incomprehensibility is a great feeling."
Abe and his colleagues report this week exactly how the wacky effect of the miracle fruit works. The team used a novel system of cultured cells that allowed them to test human taste receptors at various pHs to uncover the mechanism.
The key ingredient in the fruit, a protein known as miraculin, binds strongly to the sweet taste receptors on our tongues, Abe reported, but it does not activate the receptors at neutral pH.
When acid is introduced, the miraculin protein changes shape in such a way that it turns on the sweet receptors it is bound to, creating a sensation of ultra-sweet without affecting the other flavors in the food.
After the acidic food is swallowed, miraculin returns to the inactive shape, but it remains bound to the sweet receptor for up to an hour, ready to receive a new acid trigger. The strong binding explains the molecule's lasting effect.
While flavor-tripping has driven demand for the miracle fruit, which grows natively in West Africa, its ability to make things taste sweet without the calories that accompany sugar, makes it an intriguing candidate for a non-calorie sweetener.
The new findings show "the sweetness of miraculin at acidic pH in the mouth is the strongest of almost all the known sweeteners," Abe noted. "This will lead to industrial use of this non-calorie sweetener."
Miracle fruit is bred for sale in Japan, where it is served in some restaurants, and production of the purified miraculin protein is being pursued, Abe said.
Meanwhile, its status in the U.S. is murky. Sale of purified miraculin was disallowed in 1974 by a Food and Drug Administration ruling. But Gollner's numerous efforts to clarify the legal status of the whole fruit ended in frustration.
Nonetheless, the fruit is available, for example via miraclefruitman.com, along with miracle fruit gum and lollipops. The site advertises the fruit's suitability for diabetics, since it provides sweetness with no sugar. It also claims to be useful for chemotherapy patients, whose taste is often distorted by an unpleasant metallic cast. The miracle fruit may improve the taste of foods for some patients.