Citric acid is a mild natural acid found in citrus fruits; it is responsible for the sourness of lemons and limes. In its pure form, citric acid looks pretty much exactly like granulated sugar and acts as a natural preservative and a tart flavouring. It is sometimes used in the making of wine and ice cream, and is widely used in softdrinks, sour candies and other recipes to mimic the flavour of fresh lemon.