Submitted to: Journal of American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2007
Publication Date: 7/15/2007
Citation: Duke, S.H., Henson, C.A. 2007. Green Malt Osmolyte Concentration as an Early Indicator of Finished Malt Quality. Journal of American Society of Brewing Chemists. 65(3):145-150. Interpretive Summary: Malting quality is typically defined by the results of 10 – 15 different tests which range from simple and inexpensive to conduct (e.g. - kernel plumpness) to difficult and expensive to conduct (e.g. - beta-glucan and protein content, alpha-amylase activity, diastatic power and malt extract). Maltsters continue to seek additional measures of malt quality, especially those that are easy to perform and require only minor investments of capital to conduct. This study examined the utility of using measurements of the concentrations of total solutes in water extracts of barley malts that were unkilned (green malts) as predictors of the quality of kilned (finished) malts. A vapor pressure osmometer, the instrument required to determine the concentrations of solutes, which are called osmolytes, is small, rugged and inexpensive in addition to being very easy to use. The result of our work reported here is the demonstration that the osmolyte concentrations of green malts germinated for one and two days do predict the quality, as defined by traditional measures of malt quality, of finished malts germinated for three to six days. This rapid, easy and inexpensive measure of osmolyte concentrations at day one and two of malting will have a positive impact on the maltster as it allows them to monitor the malting process early when process conditions can be adjusted to enhance the quality of the final product.
Technical Abstract: This study was conducted to test the hypothesis that barley green malt osmolyte concentration (GMOC) can be used as an early indicator of finished barley malt quality. Seeds of three six-row and three two-row genotypes were steeped and germinated in a mircomalter for six days. At intervals of 24 h over the germination regime, green malt, from each cultivar was both removed and tested for GMOC and kilned and analyzed for the finished malt quality measurements of malt extract (ME), diastatic power (DP), '-amylase activity, soluble/total protein (S/T), and '-glucan concentration. GMOC values increased most rapidly from days one to three of germination. Except for cv. Robust, after three days rates of increase in GMOC values began to slow and/or plateau. ME followed a similar pattern to that of GMOC, but the rates of increase in ME levels began to slow and/or plateau sooner than for GMOC values. ME and GMOC values for all genotypes combined and for each genotype individually were significantly and positively correlated over the six days of germination (r=0.840, P<0.0001, combined; r=0.878 to 0.943, P<0.0001, individually). Significant correlations were also found between GMOC and other finished malt quality parameters over the six days of germination for all genotypes combined and individual genotypes ('-amylase activity, DP, and S/T were positive, r= 0.757 to 0.835, P<0.0001 combined, r=0.737 to 0.944, P=0.0006 to <0.0001 individually; '-glucan concentrations were negative, r=-0.851, P<0.0001 combined, and '-glucan concentration was negative, r=-0.851, P=<0.0001 combined, individually r=-0.788, P=0.0001 to P<0.0001). GMOC values on day one were significantly and positively correlated with ME on days one through five (r=0.756 to 0.886, P=0.0003 to <0.0001) and GMOC values on day two were significantly and positively correlated with ME on days one through six (r=0.769 to 0.910, P=0.0002 to <0.0001). This indicates that GMOC values from early periods in germination (days 1 and 2) are good indicators of finished malt ME and other finished malt quality values from malt produced one to four days later.