Roasting of coffee under different pressure conditions was also responsible for different rates of browning. Fig. 2 shows the lightness and hue angle changes of coffee beans subjected to conventional, combined conventional-vacuum and vacuum roasting processes as a function of the F value. As known, a decrease in these two colour parameters is an index of browning development due to the formation of melanoidins (i.e. the brown polymers that are formed during the final stage of the Maillard reaction).