The development of the characteristic flavour of toffee has been investigated by a number of different methods. Macroscopic changes in the constituents of toffee due to the cooking process have been measured by standard methods and related to the chemical processes taking place in the system. The importance of reaction intermediates (Strecker aldehydes and 5-hydroxymethylfurfural) in the development of toffee flavour has been determined by the use of trained taste panels and chemical analysis involving extensive use of gas-liquid chromatography. The role played by butter in the development of toffee flavour has been investigated, with particular reference to aldehydes and carboxylic acids, by the use of trained taste panels and chemical analysis involving vacuum steam distillation techniques, followed by gas chromatography.