Citric acid is a natural compound, present in all animal and vegetable material.

Citric acid is essential for the citric acid cycle, which is one of the important pathways in a series of reactions in which sugar is oxidised into carbon dioxide and water with the release of energy. This conversion occurs in every living cell. Every cell needs energy, which is harnessed in the form of a compound known as ATP. ATP is mainly produced in the reactions of the citric acid cycle ; therefore the citric acid cycle is essential for respiration. Without citric acid living cells could not function.

Citric acid is the most widely used acid and pH control agent in the food industry. It strengthens the work of antioxidants such as ascorbic acid (vitamin C, E300), and prevents fruits from turning brownish; it is also used as an acidulant in the production of beer and jam. Citric acid stabilises sweets and confectionery, to prevent crystallisation of sugar.

Citric acid is present in large quantities in fruits, especially citrus fruits, in which it is predominant. In view of the fact that the isolation of citric acid from fruits is very expensive, it is commercially produced from sugar with the help of bacteria and yeasts.