EVERYDAY SCIENCE

Detailed explanation-1: -When milk turns sour, the bacteria are converting the lactose sugars in milk into energy, with lactic acid as a byproduct. The souring of milk results in the production of sour-tasting lactic acid. In this chemical process, new substances that are lactic acid have been formed.

Detailed explanation-2: -The souring of milk is classified as a chemical change because it results in the production of sour-tasting lactic acid.

Detailed explanation-3: -The rising acidity literally sours the milk, and causes the milk proteins to coagulate. Casein, the major protein in milk, is the compound that-suspended in minuscule particles in water-makes milk look white. Acid causes the casein molecules to clump together (curdle), forming soft lumps called curds.

Detailed explanation-4: -In all types of heat treatment, the Maillard reaction occurs in milk. The Maillard reaction (nonenzymatic glycation) is a chemical reaction between amino group and carbonyl group; it is the extremely complex reaction that usually takes place during food processing or storage.

Detailed explanation-5: -However, the chemical equation of spoiled milk is C12H22O11+H2O→4CH3CH (OH) COOH.