MICROWAVE AND CONVECTIVE DRYING OF GRAPES

Thompson seedless grapes were dried under forced convection and also c ombined convection and microwaves in a modified microwave (MW) oven. E ffect of chemical pretreatment on drying rate was compared with fruits with no pretreatment. Different air temperatures and power levels wer e investigated. Dipping of fruits in hot alkaline solution of ethyl ol eate considerably reduced drying time resulting in better quality rais ins. MW drying reduced drying time resulting in raisins of comparable product quality even without chemical pretreatment. An air temperature of 50 degrees C was found to be optimum for MW drying. Page's equatio n fitted the MW drying data adequately well and the estimated paramete rs of the equation are presented.