A Comparison of Barley Malt Quality Measurements and Malt Sugar Concentrations

Abstract

This study was conducted to test two hypotheses: 1) that malt osmolyte concentration (OC) values would be better correlated with malt sugar concentrations than malt extract (ME) values; and 2) that malt α-amylase activity (α-AA) would be better correlated with malt sugar concentrations than diastatic power (DP). Seeds of four two-row and four six-row barley genotypes were steeped and germinated in a micromalter for 6 days. At intervals of 24 hr throughout germination, green malt was removed and kilned and then assayed for ME, OC, DP, α-AA, and sugar concentrations. Sugars were extracted from milled malt in H2O at 70°C for 30 min. Except for cv. Harrington, total sugars increased throughout the entire 6 days of the germination regime in two-row genotypes but either declined or plateaued after 4 days of germination in the six-row genotypes. Over all days of germination for all genotypes combined, OC correlated much better than ME with total sugar concentrations (OC: r = 0.867, P < 0.0001; ME: r = 0.589, P < 0.0001), strongly supporting the first hypothesis. When correlating individual sugar concentrations with ME and OC for all days of germination for all genotypes combined, OC also correlated much better than ME with glucose, maltose, sucrose, fructose, and the maltodextrins maltotriose through maltoheptaose (e.g., low to high r values for OC: r = 0.642 [fructose] to 0.924 and 0.928 [glucose and maltotetraose, respectively], P < 0.0001; low to high r values for ME: r = 0.282 [fructose] to 0.723 [glucose], P = 0.0524 to <0.0001), strongly supporting the first hypothesis. For all genotypes combined, α-AA correlated slightly better than DP with total sugar concentrations over all days of germination (α-AA: r = 0.743, P < 0.0001; DP: r = 0.711, P < 0.0001), supporting the second hypothesis. When correlating individual sugar concentrations with α-AA and DP for all days of germination for all genotypes combined, α-AA also correlated better than DP with most sugar concentrations (e.g., low to high r values for α-AA: r = 0.517 [fructose] to 0.900 [glucose], P = 0.0002 to <0.0001; low to high r values for DP: r = 0.412 [fructose] to 0.792 [maltotetraose], P = 0.0037 to <0.0001), supporting the second hypothesis. Overall, malt OC correlated better with malt sugar concentrations than ME, DP, or α-AA, indicating that OC best predicts starch hydrolysis during malting and a subsequent short mashing period.