Analysis of Head Rice Recovery using Different Types of Rice Mills for Two Rice Varieties Grown in Two Extreme Rice Growing Altitudes

Abstract

There have been issues of increased broken rice when farmers finally sell their rice crop, especially in the higher altitudes, and this has always been attributed to the quality of milling machines used. In this study, the head rice recovery of two rice varieties grown in high and low altitudes in Bhutan was assessed in both pre-and post-milling through manually peeling and milling in four different types of rice milling machines, respectively. The head rice recoveries on manual peeling of high and low altitude rice varieties were 54.00±0.41% and 83.68± 0.45%, respectively, and were significantly different at P<0.05. Grain crack percentages were 29.44±0.45% and 5.37±0.45%, respectively, indicating that the climatic conditions had some influence on crack development and head recovery of rice. For machine milling, the rice head recoveries were statistically significant both between varieties and among the milling machines used. The head yield was higher in low attitude variety compared to that of the high altitude one. The friction type machine with 3.32 m/s peripheral velocity gave lower head yield compared to friction type of 1.2 m/s and rubber roller type I and II milling machines. This study recommends improving the drying method presently practised in high altitudes by not laying the paddy on the ground after harvest to avoid exposure of harvested paddy to extreme day and night temperature fluctuation. The use of lower peripheral speed rice milling machines and rubber rollers is recommended to increase head yield.