A thesis submitted in partial fulfilment of the requirement for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1982

A study of expressing raw and heat-treated peanuts using a vertical continuous screw press was made. The effects of particle size and different modes of thermal preparation such as blanching, steaming and cooking upon oil yield were evaluated. The pressing of raw whole peanuts resulted in maximum oil yield and best quality in comparison with the pressing of smaller sizes. For raw peanuts, the motor amperage was determined to be a function of the screw speed and the peanut size only. The oil yield, however, could not be significantly related with any of the operational factors for raw peanuts. The optimum speeds for pressing raw and steamed peanuts were determined close to 31 and 25 rpm, respectively. The feed moisture content for general smooth operation of the screw press ranged from 7.0 to 9.5 per cent (w.b.). In pressing of steamed and blanched peanuts, the oil yield could be related with the feed moisture content and motor amperage based on the stepwise multiple linear regression analysis. A comparative evaluation of different peanut preparation modes prior to pressing revealed that conventional method of cooking gave best results in terms of oil yield, quality and energy requirements.