Hardness changes and endosperm modification during sorghum malting in grains of varying hardness and malt quality

Abstract

This study examined the interaction between sorghum grain hardness and sorghum malt quality in terms of diastatic power and free amino nitrogen with endosperm modification during malting. The changes in kernel hardness during malting of four commercial sorghum cultivars of differing quality in terms of endosperm texture and potential malt quality were measured using tests for hardness and density, and endosperm modification was followed by scanning electron microscopy. The general pattern of modification during sorghum malting was confirmed to start at the ensdosperm-scutellum interface, then into the floury endosperm towards the kernel distal end. Significantly, a cultivar of intermediate hardness and low malting quality remained harder and modified more slowly than a harder cultivar of high malting quality. It appears that intrinsic grain hardness and malt amylase and protease activity both affect malt hardness and endosperm modification, but amylase and protease activity have a greater effect due to their degradation of endosperm starch and protein. Of the hardness and density tests studied, the Tangential Abrasive Dehulling Device (TADD) gave the best measure of hardness throughout malting; maximum range 24% to 100% kernel removed over 5 days malting. Also, the data agreed with the observed malt modification rates. Thus, the TADD may have application as a simple and rapid test for estimating sorghum malt quality.