Journal of Ready to Eat Food | July-September, 2016 | Volume 03 | Issue 02 | Pages 40-44 © 2016 Jakraya JOURNAL OF READY TO EAT FOOD Journal homepage: www.jakraya.com/journal/jref ORIGINAL ARTICLE Optimization of the Drying and Tempering Parameters to Enhance the Head Rice Yield of Paddy Gajendra Prasad*, Md.I.A. Ansari** and Pramod Rai** *Department of Agricultural Engineering, Assam University, Silchar-788011, Assam, India. ** Department of Agricultural Engineering, Birsa Agricultural University, Kanke, Ranchi-834006, India. *Corresponding Author: Pramod Rai Email: pramod_kgp@yahoo.co.uk Received: 08/09/2016 Accepted: 26/09/2016 Abstract The drying and tempering process are important unit operation after harvesting of paddy. The experiments were conducted using Rotatable Central Composite Design (RCCD) technique based on Response Surface Methodology (RSM) to optimize the drying and tempering process. The independent variables taken were drying air temperature (T, º C), drying time (t d , min), and tempering time (t t , min) and response variables taken were head rice ratio (HRR), percentage point moisture removal (PPMR), drying rate (DR). The HRR decreased with increase in T and t d while with increase in t t increased the HRR. The PPMR increased with increase in T and t d . The DR increased with increase in T. The optimum operating conditions was found to be drying air temperature (74 º C), drying time (56.32 min) and tempering time (169 min). Keywords: Drying, Paddy, Tempering, Drying, Drying time. 1. Introduction One of the major problems of the rice industry is breakage of kernels during milling. Breakage in rice kernels occur because of fissure in rice kernel. Improper drying and tempering processes can be a major cause of fissuring (Ban, 1971; Kunze and Choudhury, 1972; Kunze, 1979; Sharma and Kunze, 1982; Cnossen and Siebenmorgen, 2000). Understanding the effects of drying and tempering processes on rice kernel fissuring is important to control and optimize drying and tempering conditions for maximizing milling quality. Drying is one of the oldest unit operations and yet it is one of the least understood and most complex process (Majumdar, 1996, Patil et al., 2015). The commercial dryers used for drying of agricultural products, use the heated air, which is circulated around the product for removal of moisture. The rice is tempered by being held in bins between drying passes to reduce the MC (moisture content) gradients within kernels created during drying, to achieve equilibration. The MC gradients cause differential stress inside the kernel, which, if sufficiently large, causes the kernel to fissure (Kunze, 1979). Proper tempering using high temperatures can minimize kernel damage, as measured by HRY, from severe drying conditions (Cnossen et al., 1999; Cnossen and Siebenmorgen, 2000). The objective of this study was to optimize the drying and tempering parameter for raw paddy to reduce the broken losses during milling operation. 2. Material and Methods 2.1 Materials Long grain paddy (variety: Pusa-1121) was taken for the experiment. The paddy samples were thoroughly cleaned to remove stone, dust, and chaff. The raw paddy was used for drying and its initial moisture content was 16.67% (w. b.). 2.2 Drying and Tempering The lab model dryer was used for drying. The thickness of paddy layer was kept at about 2 cm. Tempering of dried paddy was carried out by placing the sample in sealed plastic container and stored at ambient conditions. 2.3 Drying Rate (DR) The average drying rate (DR), based on wet basis, was calculated by dividing the percentage point moisture removal (PPMR) by drying time (t d ) and wet solid weight (W). d d t PPMR t W PPMR wb DR × = × = 100 ) ( 2.4 Milling