PHYSIOLOGICAL, BIOCHEMICAL AND GENETIC REGULATION OF CARBOHYDRATE METABOLISM IN CEREAL TISSUES
Location: Cereal Crops Research
Title: Tracking the progress of wort sugar production during congress mashing with North American barley cultivars and comparisons to wort osmolyte concentrations and malt extract
Submitted to: Journal of American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 18, 2011
Publication Date: November 22, 2011
Citation: Duke, S.H., Henson, C.A. 2011. Tracking the progress of wort sugar production during congress mashing with North American barley cultivars and comparisons to wort osmolyte concentrations and malt extract. Journal of American Society of Brewing Chemists. 69(4):200-213.
Interpretive Summary: For over 100 years the commercial value of malt quality has been determined primarily by what is termed “malt extract” (ME), which is a measure of the mass of material extracted from malted seeds by water. This reflects the amount of starting material in malts that is available for use by brewer’s yeast to produce the desired fermented beverage. In contrast, osmolyte concentration (OC) measurements are of the actual concentration of soluble materials in water extracts of malts. It is well established and accepted that the conversion of starch to soluble sugars is the primary process resulting in nutrients that are used by brewer’s yeast during fermentation. We have previously demonstrated that osmolyte concentrations better correlate than ME with the soluble sugars produced during the malting process. However, the amount of sugars produced during malting are a relatively small amount compared to that amount produced during mashing. This study was designed to compare the correlations of OC and ME with the production of sugars during mashing in a wide variety of commercially available barley cultivars. The results demonstrate that, for the majority of the cultivars and time points of mashing tested, OC does indeed better correlate with the production of soluble sugars than does ME. As OC is a simpler and cheaper assay than ME, the impact of this research is that brewer’s have a new alternative measure of the potential fermentation capacity of malts and that plant researchers have a fast and cheap tool with minimal labor requirements for use in the development of barley varieties with commercial malting value.
This study was conducted to test the hypotheses: (1) that the magnitude of increase in barley wort total sugar concentrations during mashing would be greater than that for malt extract (ME) and more closely reflect increases in wort osmolyte concentrations (OC), and (2) wort sugars would correlate better with OC than ME. Malts of 6 two-row and 6 six-row barley cultivars were mashed in a micro-masher and aliquots removed for wort sugar separation and quantification at 6 time points during the 115 min mashing regime. Over the first 55 min of mashing total sugars for all cultivars combined increased 110% as compared to 120% and 91% for OC and ME, respectively. At the end of the mashing regime (115 min) total sugars for all cultivars combined increased to 116% as compared to 132% and 91-92% for OC and ME, respectively. These data indicate that starch conversion to fermentable sugars is more closely reflected by OC than ME and that after 55min of mashing both sugars and OC continue to increase due to degradation starch (sugars and OC) and other malt components (OC) to lower mol. wt. compounds In contrast, the mass of material in solution, as determined by ME, remains about the same, supporting the first hypothesis. Least squared difference analysis of all cultivars combined for OC, ME, and total sugars at each time point assayed over the course of mashing revealed that both OC and total sugars increased significantly from 55 to 70ºC whereas ME did not, also supporting the first hypothesis. Over all time points in mashing for all genotypes combined, OC correlated better than ME with total sugar concentrations (OC: r=0.961, P<0.0001, ME: r=0.948, P<0.0001), supporting the second hypothesis. In correlations of individual sugar concentrations with ME and OC for all mashing time points for all genotypes combined, OC also correlated better than ME with all sugars and maltodextins (glucose, maltose, sucrose, fructose, and the maltodextrins, maltotriose through maltoheptaose, e.g., low to high r values for OC: r = 0.306, P=0.0089 [sucrose] to r = 0.959, P<0.0001 [glucose]; ME: r = 0.294, P=0.0122 [sucrose] to r =0.927, P<0.0001 [maltotetraose]), supporting the second hypothesis. Among the 12 cultivars, total sugar production during mashing correlated better with OC than with ME in 7 cultivars, correlated equally with OC and ME for 3 cultivars and correlated better with ME than OC in just 2 cultivars. These results largely support the two aforementioned hypotheses.