Milk, whether it is sour or not, is a mixture and thus does not have a chemical formula. It is made sour by lactic acid, which has the formula C3H6O3.

salt

Sour gas is a natural fuel gas that has high concentration of H2S (hydrogen sulfide). The sulfide gives the gas an unpleasant odour like that of rotting eggs. When burned sour gas releases SO2 (sulfur dioxide) an acid gas that can corrode metals. Acid are often referred to as sour as the origin of the word is from the Germanic word sauer or acidic

Lactic acid.

There are other flavor compounds formed in small amounts, like diacetyl, acetic acid, and dimethyl sulfide.

• A sour taste is chemical and it can be caused by anything from bad teeth; problems with digesting food; Acid Relux where the acid comes from the stomach up through the throat to the back of the throat giving off a acidic and sour taste in the mouth so, it's part hormonal and chemical.