Lactic acid, also known as milk acid, is found primarily in sour milk products, such as yogurt, kefir, koumiss, laban, and some cottage cheeses.

The casein in fermented milk is coagulated (curdled) by lactic acid.

Lactic acid is also responsible for the sour flavor of sourdough breads.

This acid is used in beer brewing to lower the pH and increase the body of the beer. It is also used in various beverages and cocktails to impart a sour taste.

Other application includes: pickled vegetables, wine, sauerkraut, kimchi, and fermented soy foods like soy sauce and miso.

Besides food and beverage, it can be used in cosmetics and pharma industry.