We just got a chance to taste these Sour Skittles and they are really making our lips pucker !!
According to eHow:
Tongues sense sourness because one of the most common tastes occurring in expired food is sour. The primary function of the sensitivity is bodily protection. However, a number of safe, if not pleasurable, foods taste sour. The flavor occurs naturally in citrus fruits, such as lemons, limes, oranges and grapefruits. Other fruits may taste sour, or tart, depending on their ripeness. Processed foods created to replicate these flavors also taste sour, primarily candy products. The flavor is so pleasing to some people that candymakers create many kinds of candy that taste numbingly sour in an attempt to elicit a puckered reaction.