Originally derived from citrus fruits, the so-called "sour salt" is used as a flavor enhancer and a preservative. For the homecook, use it in fruit preservation, to emulsify ice cream, or to make soft cheeses like ricotta or paneer. It's also a useful replacement for lemon or lime juice when you don't have any on hand, but you need that sharp acidic brightness.
 
Note about refill bags: 1x refill bag size is the same volume as a large jar. 2x refill bag size is double the volume of a large jar. 3x refill bag size is triple the volume of a large jar.