Citric acid is a natural flavoring found in citrus fruits like lemons and lime. It gives sour candies like Warheads and Sour Skittles their extra-sour burst of flavor.
You can find citric acid in seasoning packets and marinades, but it's also used to preserve food and can be used for a wide variety of medical and cleaning purposes.
For an extra citrusy popcorn experience, add a dash of lemon or lime zest to your popcorn. This combination will combine the sour flavors you love with an added fresh element.
You can also experiment with sour and spicy by adding a touch of cayenne powder, ground peppercorns, or even orange zest with your citric acid popcorn.