"Lactic acid is an organic acid. It has a molecular formula CH3CH(OH)CO2H. It is white in solid state and it is miscible with water. While in liquid state (dissolved state) it is a colorless solution. In industry, lactic acid fermentation is performed by lactic acid bacteria, which convert simple carbohydrates such as glucose, sucrose, or galactose to lactic acid." (from Wikipedia)

While it is most commonly used in the procuction of other products, such as yogurts, sauerkraut and some types of cheese, it is found in the composition of sourdough breads, due to the concentration of lactic acid bacteria in the sourdough starter.