Organic acid found in Citrus Fruits.
It is used to add acid in wine making (decrease pH), which will can help balance wines that seem flabby or are too sweet. It also helps reduce the potential for spoilage organisms to grow.
Citric acid can also be used in cheese making and making candy. In addition to being a natural preservative, it adds an acidic bite, or a sour tartness to foods...think sweet tarts.