Water diffusion and enzyme activities during malting of barley grains: A relationship assessment

► We identify water diffusivity in four barleys displaying distinct malting qualities. ► We quantify the hydrolytic enzymatic activities after a standard steeping diagram. ► Water diffusion is not the limiting factor for malt quality. ► Enzymatic activities play the major role on malt quality. ► Water diffusivity is affected by the endosperm structure. Maximal water uptake and diffusivity were determined from experimental soaking curves using analytical solution of the second Fick’s law in four barley samples displaying distinct hydrolytic activities during malting. Water diffusivities in the whole grains, were found to vary between 5.28 and 7.61×10−12m2/s, whereas those of the endosperms were 5–7-fold higher, ranging between 35.2 and 49.5×10−12m2/s. These differences highlighted the potential barrier role of the grain outer layers. The relationships between maximal water uptake, water diffusivity and grain biochemical and structural parameters (i.e. hardness and other less studied parameters such as vitreousness and porosity) was investigated. The lowest water diffusivity value was obtained for the barley sample displaying the lowest porosity, highest hardness and vitreousness but the highest enzymatic activity during malting, in contradiction with what is generally stated. Water diffusion was not found as the limiting factor for malt quality and, thus, its role during barley steeping has to be reconsidered.