Effect of Grain Shape and Pre-soaking on Cooking Time and Cooking Energy

Abstract

Rice is the staple food of Sri Lankans with a per capita rice consumption of approximately 114 kg/year in 2010. Parboiled rice is gaining more popularity among Sri Lankans as it is healthier than raw rice. Households spend much of their energy on cooking, and parboiled rice consumes more energy than raw rice. A slender (Bg 94-1) and a medium (Bg 360) shaped rice varieties were selected and the optimum soaking duration was calculated using the Peleg's model. The optimum rice to water ratio was determined by cooking rice samples in a rice cooker till no opaque core was observed when pressed between two glass plates. A two factor factorial experiment was carried out to determine the cooking time and energy required for cooking considering the grain type and the precook condition (soaked, and un-soaked) using an electric rice cooker and a digital watt meter. The optimum soaking duration was found to be 150 min for Bg 94-1 and 44 min for Bg 360. The optimum rice: water ratio for cooking both rice varieties was 1:2.5. The main effect of both factors was significant (p<0.05) while the interaction was not significant (p0.05) for both cooking energy and cooking time. Medium shaped rice variety required 18% less cooking time compared to slender rice variety. Moreover, the energy spent for cooking of medium variety was 19% less than that of the slender variety. Further, pre-soaking of grains up to 86% saturation was found to reduce cooking energy and time by 17 and 18%, respectively.