During the manufacture of breakfast cereals, browning reactions occur when wheat grains are cooked by direct contact with saturated steam at elevated pressure. The development of surface colour during steaming has been quantified, as a function of cook time, steam pressure and salt content, by measuring standard L*, a* and b* colour parameters. Colour reactions have a significant effect on the lightness (L*) and blue-yellow (b*) parameters only. The interior pattern of colouration has been recorded by photomicroscopy of sectioned grains. Grains cooked for shorter times generally have a white central region surrounded by darker material. When cooked for longer, the white centres disappear, by colour developing fairly uniformly within the central region, discounting the belief that the dark layer progressively extends inwards. The results on interior colour development contribute significantly to a recent debate regarding the fundamental mechanism by which cooking proceeds. (C) 2002 Elsevier Science Ltd. All rights reserved.