|DUKE, STANLEY - University Of Wisconsin|
Submitted to: Journal of the American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2010
Publication Date: 2/18/2011
Citation: Duke, S.H., Henson, C.A. 2011. Tracking the progress of congress mashing with osmolyte concentrations and malt extract values in North American barley cultivars and relationships between wort osmolyte concentrations, malt extract values and ASBC measures of malt quality. Journal of American Society of Brewing Chemists. 69(1):28-38.
Interpretive Summary: This work was designed to test the utility of a new method for assessing the potential of barley seeds to be useful to maltsters and brewers. The assay is based on measurement of the molarity of the liquid produced after germinated barley seeds are extracted with water and uses a vapor pressure osmometer to determine the concentration of materials extracted. This liquid is the nutrient broth that supports fermentation by brewer's yeast and, as such, must contain the proper blend and concentration of nutrients. This work demonstrated that extracts from germinated barley seeds that have high malting quality can readily be distinguished from those of lessor quality by this method. Furthermore, this new method can discriminate between genotypes with varying levels of malting potential better than the method that has been in use since the late 1700's and was finally standardized in the late 1800's. The impact of this work is that maltsters, brewers and barley geneticists breeding for malt quality have another quality analysis tool that has the advantage of being cheap, fast and simple.
Technical Abstract: This study was conducted to test three hypotheses: (1) that barley malt osmolyte concentration (OC) would increase more rapidly during mashing than malt extract (ME), (2) OC would better discriminate between differing barley malts during mashing than ME, and (3) that OC after mashing would better correlate with ASBC measures of malt quality than ME. Malts of 6 two-row and 6 six-row barley cultivars were mashed in a micro-masher and aliquots removed for wort OC and ME measurements at 6 time points during the 115 min mashing regime. Over the first 55 min of mashing, for all cultivars combined, wort OC values increased 120% as compared to 91% for ME. At the end of the mashing regime (115 min) wort OC values further increased to 132% whereas wort ME values remained about the same (91-92%). This indicates that the mass of material in wort remains about the same after 55 min but is further degraded to lower mol. wt. compounds increasing the wort molarity and thus OC, but not ME. Steptoe, a feed barley, was much more separated from elite malting cultivars by wort OC than by ME values throughout the mashing regime. Except for very early in mashing (5 min), there was better separation of all cultivars with OC than by ME values throughout mashing as determined with LSD analysis, indicating that OC may be better than ME in judging differences in cultivar malt quality. Linear correlations of time course mash OC vs. ME values were excellent for all cultivars combined (r=0.977, P<0001) and for 2- and 6-row cultivars separately. Correlations of the 115 min mashing OC and ME values with malt ASBC quality measurements were considerably better for OC than ME [e.g. wort protein (OC, r=0.819, P=0.001; ME, r=0.407, P=0.189), DP (OC, r=0.765 P=0.004; ME, r=0.287, P=0.365), a-amylase (OC, r=0.737, P=0.006; ME, r=0.584, P=0.046), ß-glucan (OC, r=-0.0.754, P=0.005; ME, r=-0.0.595, P=0.041)]. This study supports all three proposed hypotheses.