Sour sanding

Sour sanding, or sour sugar, is a food ingredient that is used to impart a sour flavor, made from citric or tartaric acid and sugar. It is used to coat sour candies such as lemon drops and Sour Patch Kids, or to make hard candies taste tart, such as SweeTarts.
Eating sour candies can cause irritation of the tongue because of the acid effect. It can also cause irreversible dental erosion.