Submitted to: Journal of American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2008
Publication Date: 8/15/2008
Citation: Duke, S.H., Henson, C.A. 2008. A comparison of barley malt quality measurements and malt sugar concentrations. Journal of American Society of Brewing Chemists. 66(3):151-161. Interpretive Summary: The research conducted resulted in the demonstration that osmolyte concentration is a rapid, simple and inexpensive indirect method to measure the amount of sugars produced during germination of barley seeds. This work further demonstrated that this new method better predicts starch conversion to sugars than does the determination of extract, the internationally accepted measure used to monitor the malting quality of barley. Because the ability of malted barley to rapidly convert starch to fermentable sugar is the primary quality criteria used to assess malt quality for brewing purposes and because the measure of osmolyte concentration is so rapid, simple and inexpensive, the use of this new method provides a ready tool for quality control monitoring of the malting process. Application of this new method should help maltsters ensure that under-malting or over-malting does not occur. Additionally, this new tool provides a quick, inexpensive screen of malt quality that plant breeder’s can use during early stages of cultivar development.
Technical 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 are malt extract (ME) values and (2) malt alpha-amylase activity (alpha-AA) would be better correlated with malt sugar concentrations than is diastatic power (DP). Seeds of four two-row and four six-row barley genotypes were steeped and germinated in a mircomalter for4 6 days. At 24 hr intervals throughout the germination regime, green malt was removed, kilned then assayed for ME, OC, DP, alpha-AA and sugar concentrations. Total sugars increased over the entire 6 day germination period in two-row genotypes but either declined or plateaued after 4 days 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 r=0.924 and 0.928 (glucose and maltotetraose, respectively), P<0.0001; low to high r values for ME, r=0.282 (fructose) to r=0.723 (glucose), P=0.00524 to <0.0001), also strongly supporting the first hypothesis. For all genotypes combined, alpha-AA correlated slightly better than DP with total sugar concentrations over all days of germination (alpha-AA, r=0.743, P<0.0001; DP, r=0.711, P<0.0001), supporting the second hypothesis. When correlating individual sugar concentrations with alpha-AA and DP for all days of germination for all genotypes combined, alpha-AA also correlated better than DP with most sugar concentrations [e.g. low to high r values for alpha-AA, r=0.517 (fructose) to r=0.900 (glucose), P=0.002 to <0.0001; low to high r values for DP, r=0.412 (fructose) to r=0.792 (maltotetraose), P=0.0037 to <0.0001], supporting the second hypothesis. Overall, malt OC correlated much better with malt sugar concentrations than ME, DP, or alpha-AA, indicating that OC best predicts starch conversion to sugars during germination.