Citric acid is probably way under your radar, but you almost certainly eat many foods that it's used in, like preserves, candy, and crunchy snacks.
So what is this ubiquitous ingredient? Citric acid is a natural, weak organic acid that is found in many fruits and vegetables, especially citrus fruits, hence their name. 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 in the ingredient list of many of the foods in your kitchen pantry.
Production of Citric Acid
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. Plus, 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 Aspergillus 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. Dr. Currie's technique still is used to produce citric acid today.
Citric Acid Uses in Food
About 50 percent of the world’s citric acid production is used as a flavor enhancer in beverages. Citric acid creates a slightly tart, refreshing flavor and balances the sweetness in sodas, teas, juices, and other drinks.
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 also be used in dry foods when a sour flavor is desired. Citric acid is 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 need an acidic pH for absorption. Citric acid is added to vitamin supplements to make some vitamins biologically available for absorption.
Availability of Citric Acid
Citric acid can be bought in powder form and is usually available in stores with other home canning supplies. Citric acid can 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."