Evaluation of rice milling quality and energy requirement via a developed vibratory rice grader

Abstract

In one of the approaches used in processing rice, rice is usually parboiled before milling operation and grading is one of the milling operations required to classify rice into different grades of importance viz. the head and broken rice. In this study, a vibratory rice grader was developed. The effect of processing conditions on the milling quality (milling recovery, head milled rice and broken rice), grading time, energy requirement and energy intensity were evaluated. Taguchi experimental design (L933) was used to interact the soaking time (4 – 6 h), steaming time (30 – 40 mins) and rice variety (FARO 15, FARO 60 and FARO 62). Standard equations were used to evaluate the effect of processing conditions on the milling quality, energy requirement and energy intensity. Milling recovery ranged from 53% to 70%, head milled rice (41% - 67%), broken milled rice (3% - 12%), grading time (4.4 – 5.8 mins), energy requirement (2.632 MJ to 2.649 MJ) and energy intensity (1.20 – 1.58 MJ/kg). An increase in soaking time and steaming time increased the grading time, milling recovery, head milled rice, energy requirement and energy intensity but reduced the broken milled rice. The estimated cost of the developed vibratory rice grader was $151. This study provides valuable information on a simple way of designing and developing a rice grader that could be adopted for grading rice into whole rice or head rice and broken rice.