Citric acid is a weak organic acid, and is triprotic. It is a natural preservative and is also used to add an acidic, or sour, taste to foods and soft drinks. In biochemistry, it is important as an intermediate in the citric acid cycle and therefore occurs in the metabolism of almost all living things. It also serves as an environmentally benign cleaning agent and acts as an antioxidant.

Citric acid exists in a variety of fruits and vegetables, most notably citrus fruits. Lemons and limes have particularly high concentrations of the acid; It can constitute as much as 8% of the dry weight of these fruits (1.44 and 1.38 grams per ounce of the juices, respectively[1]). The concentrations of citric acid in citrus fruits range from. 005 mol/L for oranges and grapefruits to. 030 mol/L in lemons and limes. These values will vary depending on the circumstances in which the fruit was grown.