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). Only slight differences in lightness (Fig. 2a) were observed among the different samples. By contrast, the decrease in hue angle (Fig. 2b) was greater in the vacuum-processed coffee up to an F value of approximately 3.8 min. At increasing F values, browning was significantly higher for the conventionally roasted coffee. Nevertheless, these differences in hue angle were almost not appreciable by visual observation of the medium and dark roasted ground samples (Table 2).