Lactic acid comes from fermented foods such as yogurt, cheese, pickles, sourdough bread and some types of cured meat and sausage. Bacteria produces lactic acid during the fermentation process. When added to packaged foods, lactic acid alters flavor and deters spoilage.
Some sources of dietary lactic acid are sauerkraut, kimchi, kefir and certain types of bread. The process of making these foods involves introducing lactic acid bacteria to the food and allowing it time to ferment. Lactic acid bacteria refers to a number of different strains of bacteria that are found in the human body and produce lactic acid, such as Lactobacillus acidophilus. Fermenting foods with these bacteria lends the food a slightly sour or tart flavor.
Lactic acid is used as an additive in cured meat, poultry and fish to extend shelf life, protect the flavor of the foods and to stop the growth of other potentially harmful strains of bacteria. In juices and soft drinks, lactic acid is sometimes used as an acidity regulator. Lactic acid bacteria may also be found in drinks such as wine and kombucha. In candy and confectionery, lactic acid helps to reduce stickiness and increase shelf life. Sour breads and sour grain porridge rely on lactic acid for their flavor.