Potassium benzoate is a food preservative, and is also used to make the whistling sound in many fireworks. In acidic foods with a pH level below 4.5, potassium benzoate becomes benzoic acid and slows the growth of certain bacteria, mold and yeast. As of 2011, potassium benzoate was an approved food preservative in the United States, Canada and the European Union. In the E.U., it is referred to as E212.

Fruit Juice
Potassium benzoate is commonly added to acidic fruit juices such as orange juice, apple juice, grapefruit juice or squeezed lemonade. Fresh fruit juices that require refrigeration are less likely to contain chemical preservatives than the cheaper, from-concentrate fruit juices found in the non-refrigerated aisles of the supermarket. Check the label for potassium benzoate, benzoic acid and sodium benzoate if you want to avoid benzoic acid in your fruit juice.

Soft Drinks
Potassium benzoate is commonly added to soft drinks containing phosphoric acid and sparkling drinks containing carbonic acid. Drink manufacturers in the United States are required to list potassium benzoate on the ingredients label. Regular and diet cola-type beverages commonly list potassium benzoate as an ingredient for the purpose of preserving freshness. Seltzer and soda-type carbonated drinks may contain potassium benzoate when the drink also contains an acidic component, such as citric acid from fruit extracts.

Pickles
Lactic acid is produced when food ferments, and is produced by the degradation of sugar in pickles and pickled products such as sauerkraut. Lactic acid controls the growth of certain bacteria. In pickled products, potassium benzoate is added to control the growth of yeasts and molds that are not inhibited by lactic acid. Other salts such as sodium benzoate may be used in place of potassium benzoate in pickled products.

The Center for Science in the Public Interest ranks chemical food additives according to their perceived health risks. Of five categories -- safe chemicals, chemicals to cut back on, chemicals to be used with caution, chemicals best avoided by certain people, chemicals best avoided by all people -- benzoic acid is ranked as best avoided by certain people. The E.U. recommends that potassium benzoate not be consumed by children. Since the 1990s, the Food and Drug Administration has investigated reports of the carcinogenic chemical benzene forming in foods and drinks which contain potassium benzoate or benzoic acid.