The science behind that sweet feeling
The flavour-modifying effect is due to a glycoprotein called Miraculin (hence the name Miracle Berry), in the berry. Miraculin binds to receptors on the taste buds and as a result, these proteins (known as "sweet receptors") respond to acidic or sour foods in a way that creates a sweet sensation.
The effect lasts from 20 minutes to 40 minutes (depending on quantity eaten and your taste buds).
The sweet intensity declines gradually as your saliva washes it away.