Critical evaluation of viscometrically determined pasting temperatures in barley malt

Modern varieties of malting barley allow mashing to proceed efficiently to enable saccharification and other biochemical processes. A prerequisite for starch hydrolysis is the disruption of starch granule structure by exceeding a grain specific pasting temperature. For grains, several viscometric methods based on the Rapid‐Visco‐Analyser were developed to determine variations in the pasting temperature reproducibly. Absolute pasting temperatures, as they are necessary to optimize the isothermal mashing process, cannot be determined owing to constructional and data evaluation related limitations. The aim of this research is to investigate and compensate for temperature deviations caused by standard data evaluation and lagging heat transfer from the heating unit into the sample. Accordingly, an improved determination of the pasting onset and a formula to compensate for temperature lags were developed. The optimized data leads to more accurate and reduced pasting temperatures compared with the standard method. The heat transfer was reproducibly quantified (Δϑ: 2.9–5.8°C) and integrated into a compensation formula (R2 = 0.99). It was found that the lag is strongly dependent on the actual sensor temperature but independent of the unpasted sample's initial viscosity. The results were applied on viscometric analyses (n = 161) to calculate the intrinsic pasting temperatures of barley malt. The determined temperature range is considerably lower than anticipated (56.7–60.5°C). Winter barley exhibits significantly lower pasting temperatures. The outcome of this work can be used to improve the accuracy of prospective analysis and to correct already existing viscometric raw data. Copyright © 2017 The Institute of Brewing & Distilling