A model describing the hydrolysis of starch catalysed by alpha-and beta-amylase in mashing was developed. The model was included in a simulation program that helps the planning of the mashing temperature profile. Measurements from laboratory scale mashings with different temperature profiles were used for estimating the model parameters for a Finnish malt made from the two-row barley variety Kymppi. An estimate for the proportion of gelatinized starch at different temperatures was also obtained. The model predictions for glucose, maltose and maltotriose concentrations were compared with independent measurements not used in the parameter estimation. The prediction errors for the final total concentration of fermentable sugars in wort (glucose, maltose and maltotriose) were +0.6 to -5.6% (3 mashings) when Kymppi malt was mashed. For the other two malts tested on the laboratory scale the prediction errors were -1.1 to -9.9% (4 mashings) and in the industrial scale mashings +4.6 to -2.6% (7 mashings). The model predicted the concentrations of active alpha- and beta-amylase to a sufficient accuracy in all experiments. Estimating the model parameters for the mashing conditions and the malt used would make the model predictions for fermentable sugar concentrations more accurate.