Optimization of Polishing Conditions for Long Grain Basmati Rice in a Laboratory Abrasive Mill

Abstract

Rice milling operation is a very energy-intensive process. The major qualities of the rice which are taken into consideration while milling are the degree of milling and head rice yield. A laboratory abrasion polisher, modified by attaching a humidifying and cooling unit, was used to polish long-grain Pusa Basmati rice in order to optimize the polishing conditions. Polishing experiments were carried out using central composite design for a factorial with a central point, at different initial grain temperatures (5–25 °C) and milling chamber temperatures (11–25 °C) at a constant humidity level of 95 ± 2% for different time intervals. Models capable of predicting the quality of milled rice were developed using response surface methodology and used to determine optimum processing conditions. Responses such as degree of milling (DOM), broken content, and specific energy consumption were used to assess product quality. Optimum milling conditions of a minimum of 10% DOM, a broken content of 8%, and a specific energy consumption of 11 kJ/DOM were obtained at a milling chamber temperature of 11 °C, an initial grain temperature of 15 °C, and a milling period of 180 s.