The brewery mashing process is an enzymatic-, time-, and temperature-dependent degradation process of viscosity creating macromolecules such as proteins, arabinoxylans, β-glucan, starch, and dextrins. This paper reports on the development of a new laboratory-based rheological method using a sensitive rotational rheometer that can determine viscosity changes in complex systems such as the brewery mashing process that contain dissolved and suspended materials. A Bohlin CS-50 rheometer, together with a specially designed star-shaped paddle rotor that enables mash particles to stay in suspension throughout measurement, was used. Studies were conducted to simulate an industrial mashing process, taking into account temperature, time, grist loads, adjunct amounts, and enzyme levels. The developed method was used to characterize the effects of different levels of malt modification. Clear correlations were made between the level of grain modification and the output rheological data points of peak viscosity at 50°C (R 2 = 0.9769), breakdown rate at 50°C (R 2 = 0.9784), peak viscosity at gel (R 2 = 0.9935), peak gel area (R 2 = 0.9943), the gelatinized starch breakdown rate at gel peak to 44 min (R 2 = 0.9736), and the rate of breakdown at 63°C at start and 63°C at end (R 2 = 0.9933). The developed rheological method is a useful tool for characterizing grain quality with regard to macromolecular viscosity compounds and the grains endogenous enzymatic capabilities.