Maybe you've heard of citric acid, or seen it listed in recipes, and wondered, "What is citric acid?" Citric acid is a natural acid that is found in many fruits. It is very bitter, and it gives fruits like lemons and limes their characteristic sour flavor. Citric acid is a common food additive and is found in everything from sodas to candies. A small amount of citric acid can boost the "tanginess" of certain candy flavors like lemon, lime, orange, and raspberry candies, and make them taste more natural and similar to the raw fruits. A larger amount of citric acid is used to produce candies that are very sour, like the sour gummy worms that have become popular.