Ingredient
Sour coatings
Three acids, three different jobs.
The story
The sour on a sweet is almost always a mixture of acids on the surface rather than through the sweet. Citric acid hits first and fades fast. Malic acid, the acid in apples, builds more slowly and lasts longer. Tartaric acid, from grapes, is sharper and drier. Fumaric acid dissolves slowest of all. A good sour coating uses several, so the sourness arrives in waves rather than all at once.
