How miracle fruit turns sour into sweet

Miracle fruit is the berry of Synsepalum dulcificum, a shrub native to West Africa, where the fruit has a long history of being eaten. The berry is small and red, with a thin layer of pulp around a single seed. The pulp tastes faintly sweet and not much else. The effect comes afterward: for a while after eating one, sour foods taste sweet.

One protein does the work

The active substance is miraculin, a protein that carries sugar chains attached to it, which makes it a glycoprotein. Kenzo Kurihara and Lloyd Beidler showed in a 1968 paper in Science that the active principle was a protein. In its working form two identical chains of 191 amino acids pair up.

Miraculin has no sweetness of its own at the pH of saliva. What it does was worked out in 2011 by a Japanese team that grew human sweet taste receptors in cultured cells and exposed them to the protein. The sweet receptor is a pair of proteins called T1R2 and T1R3 that sit on taste cells and respond to sugars and sweeteners. Miraculin binds to that receptor.

At neutral pH the bound protein acts as a brake. The cells responded less to other sweeteners when miraculin was present. As the solution around them turned acidic, between pH 6.5 and 4.8, the same bound protein switched on the receptor instead, and the cells signaled sweet. The switch happened each time acid arrived, which matches what tasters report: every bite of lemon or sip of vinegar reads as sweet again, for roughly one to two hours after a single berry.

The effect is specific to people. Mice do not taste sour solutions as sweet after miraculin, and when the researchers swapped parts of the human and mouse receptors, the response depended on the front section of human T1R2, the part that reaches out from the cell.

What a tasting feels like

The usual method is to roll the pulp of one berry, or a tablet of freeze-dried berry, around the mouth for a minute or two so the protein coats the tongue, then spit out the seed. Lemon wedges taste like sweet lemonade. Grapefruit loses its bite. Plain yogurt, sour beer and cider vinegar shift toward dessert, and the difference is largest with foods whose flavor is mostly acid.

Only the perception changes. The acid is still at full strength on the teeth, the lips and the inside of the mouth. A tasting that runs through several lemons, limes and vinegars can leave a sore mouth for exactly that reason, since the usual signal to stop never arrives. Spacing out the acidic foods and rinsing with water afterward is sensible.

Where it stands in the United States

The berry’s legal history is longer than its fame. In the 1970s a company planned to sell it as a sugar substitute, and in 1977 the FDA determined that miracle fruit berries, concentrates and extracts were unapproved food additives. In practice that kept the fruit out of packaged foods for decades.

The picture changed slightly in late 2023. A Florida grower, Miracle Fruit Farm, notified the FDA that it considered a freeze-dried powder of the deseeded fruit generally recognized as safe (GRAS) for use as a taste modifier in water-based drinks, at no more than 0.005 percent. The FDA answered that it had no questions about that conclusion and that the 1977 determination did not apply to that specific use. The letter, GRN 1144, was signed in December 2023 and reissued with a correction in January 2024.

The scope is narrow. The notice covers flavored and sweetened waters and similar drinks and excludes soft drinks, sports drinks and energy drinks, as well as infant formula and baby food. A “no questions” letter is also not an FDA approval. It means the agency did not object to the company’s own safety conclusion for the uses described. Other foods with miracle fruit added would still need their own basis.

Where it stands in the European Union

In Europe the berry counts as a novel food, since it was not widely eaten there before 1997. The European Food Safety Authority assessed pitted, freeze-dried miracle berries in 2021 following an application from a Spanish company. The applicant asked for up to 0.9 grams a day in food supplements. EFSA concluded the product was safe at 10 milligrams per kilogram of body weight a day, which works out to 0.7 grams for an adult.

The European Commission authorized it on that basis in Implementing Regulation (EU) 2021/1974. The dried fruit may be sold as or in food supplements for adults, excluding pregnant and breastfeeding women, at no more than 0.7 grams a day. It is not authorized as an ordinary food ingredient, and for five years from authorization, until December 2026, only the original applicant may market it. Both decisions, American and European, concern the dried whole fruit rather than purified miraculin, and both come with tight limits.