Microwave vacuum dryer setup and preliminary drying studies on strawberries and carrots.

A laboratory scale microwave vacuum dryer with the ability to record temporal variation of mass and temperature of a drying product was designed and built. The initial study was set up to investigate the effect of the position of a vacuum pressure control valve at two vacuum pressure levels, 6.5 and 13.3 kPa, with a fixed microwave power input of 1.5 W/g. Then, strawberry halves and carrot cubes (10 x 10 x 10 mm) were used for a preliminary study to investigate the effect on drying product temperature and the effect of input microwave powers (1, 1.5 and 2 W/g) at a fixed level of vacuum pressure (6.5 kPa). The position of the valve which allows air to pass through the vacuum container was found to provide shorter drying time and reduced the occurrence of water vapor condensation. The product temperature at the end stage of drying under continuous microwave mode was too high to ensure quality for both dried strawberry halves and carrot cubes.