Development of an inflatable solar dryer for improved postharvest handling of paddy rice in humid climates

Ana Salvatierra-Rojas, Marcus Nagle, Martin Gummert, Tom de Bruin, Joachim Müller


Abstract: Rice is the staple food for more than three billion people worldwide. Although considerable progress has been made with respect to improved breeds and production practices, losses during postharvest handling remain considerable. Drying and storage of paddy are two key stages where management can be improved. For rice, grain moisture content of 14% prevents microbiological activity, while a level of about 12% minimizes quality losses over prolonged storage periods. Due to the need for simple and economical technologies, an inflatable solar dryer (ISD) was developed based on adaptations of the Hohenheim-type solar tunnel dryer. To form a drying tunnel, transparent polyethylene (PE) film attaches by zipper to a reinforced black polyvinyl chloride (PVC) film. To reduce heat loss, a flexible multilayer floor was used along the drying area. The tunnel does not need a substructure as it is stabilized adequately from pressure created by two axial flow ventilators. During experiments, paddy was spread on the floor and mixed with a special roller bar. The ISD has been evaluated for paddy in the Philippines during both rainy and dry seasons and was subsequently optimized. Sun drying and shade drying were carried out in parallel for comparison and product was evaluated for moisture content and quality in terms of milling recovery and head rice yield. Moisture content was reduced from 23% to 14% within 26-52 h of continuous operation during the rainy season and 16% to 14% within 4-26 h of drying during the dry season. In both seasons, the final moisture content of 12% was reached after prolonged drying periods. Quality was not found to be affected with respect to drying treatment. The ISD showed advantages over sun drying, despite longer drying periods.
Keywords: paddy rice, postharvest handling, solar dryer, mobile dryer, collapsible dryer, Philippines
DOI: 10.3965/j.ijabe.20171003.2444

Citation: Salvatierra-Rojas A, Nagle M, Gummert M, de Bruin T, Müller J. Development of an inflatable solar dryer for improved postharvest handling of paddy rice in humid climates. Int J Agric & Biol Eng, 2017; 10(3): 269–282.


paddy rice, postharvest handling, solar dryer, mobile dryer, collapsible dryer, Philippines


IRRI. World rice statistics online query facility. Philippines: IRRI. 2016. htm. Accessed on [2016-01-19].

FAOSTAT. Food and agriculture organization of the United, Nations. Rome, Italy: FAO. 2016. Accessed on [2016-01-26].

Intal P S, Power J H. Trade, exchange rate, and agricultural pricing policies in the Philippines. Washington, D.C.: World Bank Comparative Studies--Political Economy of Agricultural Pricing Policy. 1990.

Svendsen M. The impact of financial autonomy on irrigation system performance in the Philippines. World Development, 1993; 21(6): 989–1005.

Coxhead I. Consequences of a food security strategy for economic welfare, income distribution and land degradation: The Philippine case. World Development, 2000; 28(1): 111–128.

Otsuka K. Role of agricultural research in poverty reduction: lessons from the Asian experience. Food Policy, 2000; 25(4): 447–462.

Mehta A, Jha S, Quising P. Self-targeted food subsidies and voice: Evidence from the Philippines. Food Policy, 2013; 41: 204–217.

De Padua D B. Philippine rice postproduction systems (PPS): moving to a brighter future. International Rice Research Institute Repository, 2013.

Sebastian L, Alviola P, Francisco S. Bridging the rice yield gap in the Philippines. In: Papademetriou M K, Dent F J, Herath E M, editors. Bridging the rice yield gap in the Asia-Pacific Region. Nueva Ecija, Philippines: FAO Regional Office for Asia and the Pacific, 2000; 222 p.

Lim J S, Abdul Manan Z, Hashim H, Wan Alwi S R. Towards an integrated, resource-efficient rice mill complex. Resources, Conservation and Recycling, 2013; 75: 41–51.

Maclean J L, Dawe D C, Hardy B, Hettel G P. Rice Almanac, 4th edition: Source book for one of the most important economic activities on earth. Wallingford: CABI, 2002.

De Padua D B. The Philippine rice post-production consortium: Need assessment of the post-production industry. In: Johnson GI LVT, Nguyen Duy Doc, Webb MC, editor. Quality assurance in agricultural produce. Ho Chi Minh City: Australian Centre for International Agricultural Research, 2000; 736 p.

Lantin R. Rice: post-harvest operation. Post-harvest compendium. Los Baños, Philippines: International Rice Research Institute. 1999. user_upload/inpho/docs/Post_Harvest_Compendium_-_RICE.pdf. Accessed on [2015-07-19].

Datta S K D. Principles and practices of rice production. John Wiley & Sons. 1981.

Loewer O J, Bridges T C, Bucklin R. On-farm drying and storage systems: American Society of Agricultural Engineers, 1994.

Bhattacharya K R. Rice quality: A guide to rice properties and analysis. Elsevier Science, 2011.

Jayas D S, White N D G, Muir W E. Stored-grain ecosystems: Taylor & Francis, 1994.

Fukushi K, Hassan K M, Honda R, Sumi A. Sustainability in food and water: An Asian perspective. Springer Netherlands, 2010.

Janier J B, Maidin M B. Paddy moisture content detector. Journal of Applied Sciences, 2011; 11(7): 1476–1478.

Adhikarinayake T B, Palipane K B, Müller J. Quality change and mass loss of paddy during airtight storage in a ferro-cement bin in Sri Lanka. Journal of Stored Products Research, 2006; 42(3): 377–390.

Prasantha B D R, Hafeel R F, Wimalasiri K M S, Pathirana UPD. End-use quality characteristics of hermetically stored paddy. Journal of Stored Products Research, 2014; 59: 158–166.

Koide N, Robertson A W, Ines A V M, Qian J H, Dewitt D G, Lucero A. Prediction of rice production in the Philippines using seasonal climate forecasts. Journal of Applied Meteorology and Climatology, 2013; 52(3): 552–569.

Phillips S, Widjaja S, Wallbridge A, Cooke R. Rice yellowing during post-harvest drying by aeration and during storage. Journal of Stored Products Research, 1988; 24(3): 173–181.

Proctor D L. Grain Storage Techniques: Evolution and Trends in Developing Countries: GASGA, 1994.

Hayami Y, Kikuchi M, Marciano E B. Middlemen and peasants in rice marketing in the Philippines. Agricultural Economics, 1999; 20(2): 79–93.

Gragasin M, Maruyama A, Kikuchi M. An economic evaluation of post-harvest technology: the case of rice and corn drying in the Philippines. Japanese Journal of Tropical Agriculture, 2004; 48(4): 253–264.

Janjai S, Esper A, Mühlbauer W. A procedure for determining the optimum collector area for a solar paddy drying system. Renewable Energy, 1994; 4(4): 409–416.

Maurer R. Untersuchung und modifikation einer solaren tunneltrocknungsanlage mit integriertem kollektor für den einsatz bei der reistrocknung in Humiden Gebieten Stuttgart: Universität Hohenheim. Institut für Agrartechnik, 1989; 112 p.

Djokoto I K, Maurer R, Muehlbauer W. Solar tunnel dryer for drying paddy. AMA (Agricultural Mechanization in Asia), 1989; 20(3): 41–43.

Bautista E, Aldas R, Gagelonia E. Rice hull furnaces for paddy drying: The Philippine rice research institute's experience. ACIAR Proc, 1996; pp.253–260.

Regalado M J C, Bekki E, Madamba P S. Dehumidification drying of high-moisture rough rice in a radial-flow, circular bin. Drying Technology, 2000; 18(10): 2307–2326.

Basunia M A, Abe T. Design and construction of a simple three-shelf solar rough rice dryer. AMA. Agricultural Mechanization in Asia, Africa and Latin America, 2001; 32(3): 54–59,66.

Amir E J, Grandegger K, Esper A, Sumarsono M, Djaya C, Mühlbauer W. Development of a multi-purpose solar tunnel dryer for use in humid tropics. Renewable Energy, 1991; 1(2): 167–176.

Lutz K, Mühlbauer W. Solar tunnel dryer with integrated collector. Drying Technology, 1986; 4(4): 583–603.

Lutz K, Mühlbauer W, Müller J, Reisinger G. Development of a multi-purpose solar crop dryer for arid zones. Solar and Wind Technology, 1987; 4(4): 417–424.

Müller J, Mühlbauer W. Solar drying. In: Tsotsas E, Mujumdar A, editors. Modern Drying Technology, Energy Savings: John Wiley & Sons, 2014; pp. 199–243.

Schirmer P, Janjai S, Esper A, Smitabhindu R, Mühlbauer W.

Experimental investigation of the performance of the solar tunnel dryer for drying bananas. Renewable Energy, 1996; 7(2): 119–129.

Janjai S, Lamlert N, Intawee P, Mahayothee B, Boonrod Y, Haewsungcharern M, et al. Solar drying of peeled longan using a side loading type solar tunnel dryer: Experimental and simulated performance. Drying Technology, 2009; 27(4): 595–605.

Bala B K, Woods J L. Simulations of the indirect natural convection solar drying of rough rice. Solar Energy, 1994; 53(3): 259–266.

Buck A L. New equations for computing vapour pressure and enhancement factor. Journal of Applied Meteorology, 1981; 20(12): 1527–1532.

ASHRAE. Fundamentals handbook. 2001.

Gummert M. Measuring rice moisture content. Los Banos-Philippines: International Rice Research Institute. 2010. Accessed on [2012-05-15].

Chen C. Evaluation of air oven moisture content determination methods for rough rice. Biosystems Engineering, 2003; 86(4): 447–457.

Perdon A, Siebenmorgen T J, Mauromoustakos A. Glassy state transition and rice drying: Development of a brown rice state diagram. Cereal Chemistry, 2000; 77(6): 708–713.

Juliano B O. Rice in human nutrition. Cereals international proceedings of an international conference, Brisbane, Australia, 9-13 Sept. 1991. Martin D J and Wrigley C W, eds. Cereal Chemistry Division, Royal Australian Chemical Institute, Parkville, Victoria, 3052 Australia. pp. 31–34.

Laborte A G, Paguirigan N C, Moya P F, Nelson A, Sparks A H, Gregorio G B. Farmers' preference for rice traits: Insights from farm surveys in Central Luzon, Philippines, 1966-2012. PLoS ONE, 2012; 10(8): e0136562.

Chen X D, Mujumdar A S. Drying technologies in food processing. John Wiley & Sons, 2009. 352 p.

Banaszek M M, Siebenmorgen T J. Head rice yield reduction rates caused by moisture adsorption. Transactions of the ASABE, 1990; 33(4): 1263–1269.

Ondier G O, Siebenmorgen T J, Mauromoustakos A. Low-temperature, low-relative humidity drying of rough rice. Journal of Food Engineering, 2010; 100(3): 545–550.

Ramaswamy H S, Marcotte M. Food Processing: Principles and Applications: CRC Press, 2005.

Bala B K, Mondol M R A, Biswas B K, Das Chowdury BL, Janjai S. Solar drying of pineapple using solar tunnel drier. Renewable Energy, 2003; 28(2): 183–190.

Hossain M A, Bala B K. Drying of hot chilli using solar tunnel drier. Solar Energy, 2007; 81(1): 85–92.

Gagelonia E C, Bautista E U, Regalado M J C, Aldas R E. Flatbed dryer re-introduction in the Philippines. AMA, Agricultural Mechanization in Asia, Africa and Latin America, 2001; 32(3): 60–66.

Meas P, Paterson A H J, Cleland D J, Bronlund J E, Mawson A J, Hardacre A, et al. Effects of different solar drying methods on drying time and rice grain quality. International Journal of Food Engineering, 2011; 7(5): 341–350.

Assar M, Golmohammadi M, Rajabi-Hamaneh M, Hassankiadeh M N. A combined experimental and theoretical approach to study temperature and moisture dynamic characteristics of intermittent paddy rice drying. Chemical Engineering Communications, 2016; 203(9): 1242–1250.

Cnossen A G, Jiménez M J, Siebenmorgen T J. Rice fissuring response to high drying and tempering temperatures. Journal of Food Engineering, 2003; 59(1): 61–69.

Aquerreta J, Iguaz A, Arroqui C, Vírseda P. Effect of high

temperature intermittent drying and tempering on rough rice quality. Journal of Food Engineering, 2007; 80(2): 611–618.

Dong R, Lu Z, Liu Z, Nishiyama Y, Cao W. Moisture distribution in a rice kernel during tempering drying. Journal of Food Engineering, 2009; 91(1): 126–132.

Zhou L, Liang S, Ponce K, Marundon S, Ye G, Zhao X. Factors affecting head rice yield and chalkiness in indica rice. Field Crops Research, 2015; 172: 1–10.

Zhao X, Fitzgerald M. Climate change: implications for the yield of edible pice. PLoS ONE, 2013; 8(6): e66218.

Martinez R. Modeling and simulation of the two-stage rice drying system in the Philippines. PhD dissertation. Stuttgart: Universität Hohenheim, 2001. 165 p.

GrainPro I. Solar Bubble Dryer™. Subic, Philippines. Subic: GrainPro, Inc. 2015. option=com_content&view=article&id=115&Itemid=1653#. Accessed on [2016-01-30].

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