Skip to main content
ARS Home » Southeast Area » Dawson, Georgia » National Peanut Research Laboratory » Research » Publications at this Location » Publication #187752


item Butts, Christopher - Chris

Submitted to: American Society of Agri Engineers Special Meetings and Conferences Papers
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2005
Publication Date: 7/12/2006
Citation: Harraz, H., Wang, Y., Butts, C.L. 2006. Dehydration of in-shell peanuts using radio frequency energy with intermittent stirrings. ASABE Paper No. 066048. . American Society of Agri Engineers Special Meetings and Conferences Papers.

Interpretive Summary: The conventional process of drying in-shell peanuts after harvest to moisture levels low enough for safe storage is time consuming and uses a lot of energy. It takes approximately 14-18 hours to dry peanuts from 17 to 10% moisture content and about 8-10 gallons of propane per ton of peanuts. Dielectric heating using radio frequency (RF) energy, similar to using a conventional microwave oven, has been used to rapidly dry many foods while using less energy. In-shell peanuts were dried using RF energy by heating fresh peanuts to 104 F then stirring until they reached room temperature. The heating and stirring cycle was repeated until the moisture content was reduced to acceptable levels. The tests were repeated with peanut temperatures of 122 F and 140 F. A mathematical model was developed to predict the time required to dry peanuts using RF energy. Peanut quality was comparable to conventionally dried peanuts.

Technical Abstract: Both conventional wagon drying (curing) systems and batch/continuous flow dryer systems are time and energy consuming. RF dielectric heating has been used in drying many foods to take advantages of the effective, fast heat generated by the interaction between RF energy and biological products, reducing the drying time and energy consumed. RF energy was applied in the postharvest drying (curing) of peanuts. The non-uniformity due to difference in orientation, sizes and shapes of shells as well as the location of shells in the drying container was overcome using multiple numbers of RF treatments and intermittent stirrings. A set of 6 cycles of RF treatment and intermittent stirring was used to dry peanuts at three different final temperatures of 40, 50 and 60 °C. Fiber optics thermal sensors were used in the RF experiments to monitor the change in temperature inside the kernels. With the RF drying method it took about two and half hours, including six cycles of RF heating and intermittent stirring,, to achieve the required peanut storage moisture content (less than 10.5% wet basis). The actual RF heating time was in a range of 10 to 20 minutes for final temperatures at 40 to 60°C versus 24 hours hot air blowing in conventional wagon drying (curing) systems to achieve the same moisture reduction. The total percentage decrease in moisture content was relatively fixed with a certain average heating temperature regardless of the starting moisture content of the peanuts. The heating curves of kernels during the RF treatment unit as well as the decrease in moisture content after every RF unit and intermittent stirring are illustrated in the paper. A mathematical model was developed to determine the relation of the percentage decrease of peanut moisture content with heating time at certain average heating/drying temperature.