A MODEL OF THE EFFECT OF HEATED-AIR DRYING ON THE BREAD BAKING QUALITY OF WHEAT

A model was developed of the effect of heated-air drying of wheat on bread baking quality for use in computer simulation of wheat drying. Two varieties of wheat at three initial moisture contents were dried in thin layers with air from 65 to 85 °C for periods from 1 min to 4 h to produce both records of the moisture and temperature of the grain during the drying and heat-damaged samples. The moisture and temperature within the kernels were modelled by fitting a diffusion model to the thin-layer drying curves. Moistures and temperatures of the kernel as a whole were then derived from the distributed parameters so the benefit of using the more complex diffusion model could be assessed. Two models were also used to express the dependence of the rate of loss of loaf volume, relative to controls, on temperature and moisture. The first was a model of zero order with an exponential dependence on temperature and moisture, and the second was a first-order model, using the Arrhenius equation for temperature dependence and a linear equation for moisture dependence. Both models of loaf volume loss fitted the data equally well when used with the drying model which considered the kernel as a whole. However, the diffusion drying model, in conjunction with the first-order model of loaf volume loss, produced much closer predictions and was concluded to be the best approach. Published data were used as an independent test. Good results were obtained for runs at and below 80 °C air temperature but, at 90 and 100 °C air temperature, measured damage was less severe than that predicted by the model probably because of discrepancies between actual kernel temperatures and those predicted by the diffusion model. © 1992 Silsoe Research Institute.