Soured milk is a food product produced from the acidification of milk. It is not the same as spoiled milk that has gone bad naturally, commonly also called "soured". Acidification, which gives the milk a tart taste, is achieved either through the addition of an acid, such as lemon juice or vinegar, or through bacterial fermentation. The acid causes milk to coagulate and form a thicker consistency, and inhibits the growth of harmful bacteria and thus improves its shelf life. Soured milk that is produced by bacterial fermentation is more specifically called fermented milk or cultured milk. Soured milk that is produced by the addition of an acid, with or without the addition of microbial organisms, is more specifically called acidified milk. In the United States, acids used to manufacture acidified milk include acetic acid (commonly found in vinegar), adipic acid, citric acid (commonly found in lemon juice), fumaric acid, glucono-delta-lactone, hydrochloric acid, lactic acid, malic acid, phosphoric acid, succinic acid, and tartaric acid.