Wheat grain cooking involves heating and moisture uptake. Stapley et al. (Int.. J. Food Sci. Technol. 1997, 32, 355) documented the differences between moisture uptake in boiled and steamed grains. The relationship and coupling between the heat- and mass-transfer processes is investigated here. By determining the moisture- activity diagram arising from the Stapley et al. steaming data (Chem. Eng. Sci. 1999, 54, 965), it is argued for the first time that heat transfer exerts the key controlling influence on the moisture mass transfer in steaming. A heat- and mass-transfer model for grain steaming is developed that extends and improves on the previous model (Chem. Eng. Sci. 1999, 54, 965). This model allows for the coupling of the two processes and the introduction of a dimensionless parameter, as well as providing neater solutions. In steaming, the observed temperature elevation in the grain suppresses the driving force for mass transfer. This study contributes to a better understanding of the cooking operation and will lead to improvements in batch cooking operations in breakfast cereal manufacturing.