Deep-fat frying is perhaps the most complex of food processing operations because of the multiplicity of reactions that occur and the vast quantity of chemical products that are generated. Understanding the chemical processes that occur during frying and the methods available to control oil degradation can have a big impact on finished product flavor and shelflife.
Frying is usually done in the 180°-200°C range. There are three major chemical reactions that occur: oxidation, polymerization and hydrolysis. Each of these reactions produces a wide range of compounds which contribute to the formation of both desirable and undesirable products in fried foods.