This food grade lactic acid is used for the production of several types of cheeses, especialy when UHT, ultra-pasturized or powdered milk are used as the starting materials. The inclusion of additional lactic acid prior to rennetting overcomes this shortage and improves the curd yield. Lactic acid is usually added up so that the pH of the milk is 5.0
The casein in fermented milk is coagulated (curdled) by lactic acid and it is also responsible for the sour flavor of sourdough breads.
