The potential of dielectric heating with microwaves at 2450 MHz for drying grapes into raisins was studied. Feasibility studies in a conventional microwave oven were successful. A new microwave drying system equipped with specialized instrumentation and data acquisition components and permitting full control of microwave power levels and duration of application was then developed and used for detailed experimental work. / It was found that when the grapes were dipped in surfactants, as is common practice in the raisin industry, microwave drying was not only faster than convective drying but also had a much lower specific energy requirement. However, it was also possible to obtain raisins of adequate quality without dippings. Good quality light coloured raisins were obtained without sulphur dioxide fumigation. Thus, microwave drying has potential in reducing both the quantity of chemicals entering at this point in the food chain and the energy consumed for food preservation. / The shrinkage and density of grapes were found to be linearly related to moisture content; initial size and method of drying had no influence. (Abstract shortened by UMI.)

No description available.