Effect of different analysis conditions on Rapid Visco Analyser malt viscograms in relation to malt of varying fermentability

摘要

Malt fermentability is a difficult and time consuming trait to measure. The Rapid Visco Analyser (RVA) was assessed as an alternative rapid method to indicate potential fermentability. This study evaluated changes in rheological profiles under different operational conditions and compared these changes with reference to malt fermentability from a limited number of samples. Viscosity measurements of samples were also made using different RVA (models 3D+ and 4) analysis conditions including a brewhouse time-temperature profile, heating/cooling rate, particle size and enzyme activity. Rheological measurements using the RVA-3D + gave similar results compared with the RVA-4, indicating adequate sensitivity of the RVA 3D+ for discriminatory purposes. Use of a time-temperature profile of a commercial brewery mashing process was unsuitable. When malt enzymes were inactivated with silver nitrate, differences in viscosities were observed. However, this eliminated the ability to discriminate on fermentability. Increasing or decreasing the heating rate influenced the time available for enzyme action, which affected the degree of discrimination. This also provided some insight into physical and biochemical processes affected by differences in particle size. RVA has the potential to be used as a tool to discriminate between poor and good fermentability barley malts. RVA conditions when using the 'Kilned Malt' method with an appropriate mashing malt-water ratio provided a fast and reliable indication of malt performance prior to conducting lengthy fermentability tests.