Impact of Drying Techniques on Physicochemical Properties of Dried Rice and Its Influences on Rice Beer Brewing Process

Abstract

Highlights Implications of microwave drying on rice brewing performance were tested. Microwave-dried rice is most similar to natural air-dried rice in protein and amylose content. Microwave-dried rice is most similar to natural air-dried rice in brewing utilization. Abstract. Rice is used as an adjunct grain by the beer manufacturing industry. Before utilization, the rice has to be dried to the desired moisture content. The drying process employed may have an impact on the rice’s physicochemical properties, which influence the rice’s performance in the brewing process. This study focused on investigating the impact of microwave drying on rice’s physicochemical properties and utilization in the brewing process. Rough rice samples with an initial moisture content of 19.7% wet basis were exposed to a microwave dryer to deliver specific energy at the rate of 525 kJ/Kg of initial grain mass in a single drying pass. The effects of the single-pass continuous drying on the dried rice amylose content, protein content, and specific gravity (°Plato, fermentable sugar content) of the wort were determined. The results were compared with samples dried using natural air at 25°C and 56% relative humidity (RH) and two-pass hot-air drying at 45°C and 60°C with RH set at 20%. There was a statistical difference in measured rice amylose and protein contents (p= 0.042) between microwave-dried samples and the natural air-dried samples. However, these attributes were significantly different from those of samples dried at a higher temperature of 60°C and an RH of 20%. There was a significant difference (p=0.0197) in the initial gravity content of the all-malt samples and the rice adjunct samples, as expected, but there was no significant difference between the rice adjunct samples. Overall, this study analyzed the effect of microwave drying on rice processing and its subsequent use in the brewing process, but no measurable differences were observed among the wort’s initial and final gravity contents, attenuation levels, and alcohol by volume. Microwave drying was most comparable to natural air drying, but it results in a greater head rice yield, which may benefit rice farmers and processors. Keywords: Amylose content, Brewing process, Microwave drying, Rice drying, Specific gravity.