Starch Gelatinization Properties Impacted by Growing and Process Factors and Implication to Brewing

While not commonly examined, starch gelatinization is a fundamental step that critically impacts efficiencies of brewhouse operation and fermentable sugar production. Research has demonstrated that gelatinization enthalpy for barley tends to increase with hot and dry growing conditions. In this study, samples from recent crop years were shown to have gelatinization temperatures (Tg) higher than 65 °C that is a widely used isothermal mashing temperature. Differential scanning calorimeter (DSC) analysis has shown that typical endothermic transition of barley and wheat and their malts occurs between 55 - 70 °C. Comparatively, rapid visco-analyzer (RVA) pasting curve, which closely simulates the mashing progression, presented similar trending to DSC results. It was found that the onset temperature for gelatinization does not necessarily reflect the total heat requirement to gelatinize the starch. The starch pasting process took a temperature range of 65-71˚C to complete the RVA peaking cycle. The total peak area may serve as an indicator of energy required to mash the malt, while the height of peak viscosity exhibits the potential torque level for stirring the mash. As germination progresses, the apparent on-set pasting temp (PT) appeared to increase slightly, but closing pasting temperature (Tc) shifts lower, hence peaks become smaller. Therefore, malting substantially reduces the peak viscosity and total heating energy (peak area) and makes the starch better accessible, but malting alone does not gelatinize starch significantly.  RVA results showed that the crop 2021 (drought year) samples, e.g. Synergy, needed higher thermal energy to liquify than 2020’s. It was particularly noteworthy that the RVA peak viscosity did not align with the viscosity of Congress wort which was more exhaustively extracted. Based on the observation, it is hypothesized that the small granules were preferably hydrolyzed in germination while the large ones in mashing. As small granules had been reported to have higher Tg than the large ones, leverage malting to hydrolyze small granules appears to be critical to increase the starch utilization. This study showed that grain type (millet, buckwheat, barley malt), barley variety and crop year all impacted the pasting properties of their starch component.