Effect of moisture stress on malting quality in Triumph barley

Abstract

During the 1988/1989 season, a field-scale irrigation experiment during growth of barley (cv. Triumph) was conducted in which all rainfall was excluded by a mobile rainshelter. Twelve treatments were imposed, giving a wide range of timings and durations of drought. Grain β-glucan content and malt fine extract decreased with drought stress, and both were directly proportional to seasonal transpiration. Grain nitrogen content varied widely. Mean β-glucan levels in grain, and in wort from the corresponding malt samples, were high but uncorrelated. Wort β-glucan levels were independent of drought stress level if the drought occurred after β-glucan accumulation began, but otherwise decreased as drought stress increased. The expected correlation between grain nitrogen content and fine extract was only observed for treatments in which no post-anthesis drought occurred. Grain nitrogen concentration and total nitrogen per grain varied among treatments, indicating that final nitrogen concentration was not due just to carbohydrate dilution of a predetermined amount of nitrogen uptake per grain or unit area. Best utilization of applied nitrogen was made when the plants suffered no drought. This led to the lowest grain nitrogen content and the best malt quality. Modification of the grain during malting was relatively poor when drought occurred late, compared to earlier droughts, as indicated by the relatively poor wort nitrogen/grain nitrogen ratios. A similar effect was seen for β-glucan hydrolysis during malting. The study demonstrated that careful irrigation management, especially during grain filling, is necessary for the production of high quality malting barley.