Miracle fruit (formally known as Synsepalum dulcificum) is a red berry native to West Africa. It contains a protein called miraculin that has the odd effect of making foods taste good.

[...] When miracle fruit is consumed, the miraculin in the berry binds to the taste buds on the tongue. A person has receptors on their taste buds that identify sweet, sour, bitter and savory tastes. Normally, if you were to eat a lemon, your sour receptors would start firing. [...] Under the influence of miraculin, however, the sweet receptors start signaling and suppress the sour tastes. The miraculin rewires the sweet receptors to temporarily identify acids as sugars.

[snip]

Then, for about an hour, the miraculin modifies sour foods to taste sweet. Sweet foods will taste about the same, if not overly sweet, and other flavors remain unaffected. Because miraculin is a protein, heat will destroy the effect, so the berry can’t be cooked, and heated foods won’t taste any differently. Eventually, saliva washes away the miraculin, and your tongue returns to normal.

Read on for more, including a neat conspiracy theory involving foul play at the FDA that explains why we don’t have this miracle fruit here in the US.

h/t Z.