Citric acid is a natural, weak organic acid that is found in many fruits and vegetables, especially citrus. Because citric acid is also a byproduct of the citric acid cycle, it is also produced by many living organisms, including mold.
Citric acid is prized for its sour flavor, preservative quality, and ability to act as a pH buffer. For these reasons, citric acid is found on the ingredient list of many food products today.
How is Citric Acid Produced?
Although citric acid is found in high concentrations in many citrus fruits, it is not economical to extract the acid from fruit for industrial use. Furthermore, the demand for citric acid far outweighs the supply of citrus fruit available.
The ability of the mold Aspergillus niger to produce citric acid as a byproduct of metabolism was discovered by American food chemist James Currie in 1917. The process of cultivating A. niger and allowing it to metabolize sucrose or glucose to yield citric acid proved efficient and inexpensive. Once it was possible to produce a seemingly endless supply of citric acid, companies like Pfizer and Citrique Belge began producing it on an industrial scale. This same technique is used to produce citric acid today.
Uses for Citric Acid in Food
Approximately 50% of the world’s citric acid production is used as a flavor enhancer in beverages. Citric acid is used in soft drinks, teas, juices, and other beverages to create a slightly tart, refreshing flavor and balance sweetness.
The acidic pH of citric acid also makes it useful as a preservative. Since many bacteria are unable to grow in an acidic environment, citric acid is often added to jams, jellies, candy, canned foods, and even meat products as a preservative.
Because citric acid can be made in a powder form, it can be used in dry foods when a sour flavor is desired. Citric acid is therefore a dry alternative to lemon juice or vinegar in dry foods such as seasoning salts, flavoring powders, and crunchy snacks.
Citric acid is sometimes used to create an acidic environment and facilitate the ripening process when making cheese, particularly mozzarella. Citric acid is also used to adjust the pH of solutions when brewing both beer and wine.
The acid pH of citric acid also makes it useful as a dietary supplement. Many minerals require an acidic pH for absorption. Citric acid is added to vitamin supplements to make some vitamins biologically available for absorption.
Citric Acid Availability
Citric acid can be purchased in powder form and is usually available in stores with other home canning supplies. Citric acid may also be found in natural food stores or health food stores with other vitamins and dietary supplements. In some grocery stores, citric acid is sold in small shakers and labeled as "sour salt."