Frying, especially deep frying in oil, ranks among simple and rapid food preparation techniques. In frying, exchange of water and oil take place. Main chemical reactions are hydrolytic and oxidation processes in frying oil, pyrolytic reactions in surface layers of food, and interactions between lipid oxidation products and proteins or other components of fried food, resulting in the formation of specific flavour. Loss of the nutrition value and health risks due to the oxidized oil are rather low under proper frying conditions.