Parboiling of dehusked rice N. Kar, R.K. Jain * , P.P. Srivastav Harvest and Post Harvest Technology Scheme, Department of Agricultural and Food Engineering, Indian Institute of Technology, Kharagpur 721302 India Received 5 May 1998; accepted 10 October 1998 Abstract Parboiling of dehusked rice, that is, soaking of dehusked rice at initial temperatures of 70±100°C and cooling at room tem- perature for 2 h followed by open steaming for 20 min, shade drying and polishing gives rice with quality attributes comparable with normal parboiled rice. The cooking time is reduced by at least 30%. The process saves about 40% energy and can be easily adopted by primary processors in developing countries. The rices have been organoleptically evaluated and found acceptable. Ó 1999 Elsevier Science Ltd. All rights reserved. 1. Introduction Parboiling of paddy, a hydro-thermal treatment aimed at inducing milling, nutritional and organoleptic improvements in rice, is applied to about half of the Indian and one fourth of the world paddy produce. It is one of most widespread food industries of the world (Bhattacharya, 1985, 1990; Pillaiyar, 1988). In modern parboiling practice in India, paddy is soaked in hot water, steamed to complete gelatinization and dried and milled. However, the siliceous husk oc- cupies about one fourth of paddy mass by weight and more than one third by volume (Houston, 1972) does not wet easily and is a barrier which resists water movement into the kernel. Often air is trapped within the husk and prevents access of water to the kernel. The husk has a poor thermal conductivity and slows down heat transfer to the kernel. Thus considerable time and heat energy is required in wetting and heating the husk mass. Moreover the husk is also a barrier during the drying operation after parboiling. Parboiling of dehusked rice (brown rice) is an attrac- tive alternative with the following potential advantages: 1. Natural contamination associated with the husk is avoided during soaking. 2. Colour and odour development in parboiled rice due to the presence of the husk (Luh & Mikus, 1980) dur- ing soaking is avoided. 3. Processing time and energy will be reduced and par- boiling capacity will be increased. 4. Handling cost per tonne of processed rice will be re- duced. 5. It will help in the modernization of the rice milling in- dustry by shifting parboiling between the shelling and the polishing operations. This will lead to collection of pure by-products, husk and bran. Parboiling of dehusked rice has been attempted by Abrol (1983), who recommends soaking at 70°C for 1.5 h and steaming for 12 min. However, such hot soaking requires precise control. Soaking at room temperature (traditional method of parboiling) is slow and invites microbial contamination while hot soaking (CFTRI method) requires precise control and special care because a steep temperature and moisture gradient develops and may cause sloughing-o of the surfaces before hydration up to the core of the kernel is achieved. It has been suggested that starting soaking of paddy at 75°C and allowing the batch to cool naturally ensures the fastest possible hydration without complications (Bhattacharya, 1985). In this paper simple soaking procedures using de- husked rice have been pursued to produce quality par- boiled rice with minimum process energy requirement and facilitation of adoption at rural level. 2. Materials and methods Paddy, cultivars Pankaj, Kavirajsal, IR-36 and Swarna abundantly grown in this region, were used for this study. Journal of Food Engineering 39 (1999) 17±22 * Corresponding author. Tel.: 91-03222 55221; e-mail: rkj@ phtc.iitkgp.ernet.in 0260-8774/99/$ ± see front matter Ó 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 0 - 8 7 7 4 ( 9 8 ) 0 0 1 3 8 - 1