A Comparative Nuclear Magnetic Resonance and Rheological Study on Mash and Spent Grain Suspensions, Worts, and Carbohydrate Solutions

Nuclear magnetic resonance (NMR) was used to determine the T2 NMR relaxation times of mash and spent grain suspensions, worts, and carbohydrate solutions. T2 characterizes the molecular mobility of fluids. The T2 values, furthermore, correlate with both the zero-shear-rate viscosity and the viscosity at high shear rates that have been determined with a rotational rheometer. Thus, NMR provides the possibility to determine characteristic viscosities of materials during the brewing process by means of T2 experiments. The viscosities of the mash and the wort are important process parameters, since they are used 1) as a process and quality control of the brewing and filtering/lautering processes, and 2) for the determination of the wort density as a measure of the dissolving process of carbohydrates in spent grain. This NMR application, which has comparatively short measuring times, is especially interesting for use with dispersal systems in which the use of conventional rheometric techniques may cause great errors. The only prerequisite for measuring viscosities using NMR is a previous calibration.