Understanding Wheat Grain Steaming

Wheat grain cooking involves heating and moisture uptake. Stapley et al. (Int. J. Food Sci. Technol. <BO>1997</BO>, 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. <BO>1999</BO>, 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. <BO>1999</BO>, 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.