Temperature distribution and measurement for Grape Puffs(TM) in the microwave vacuum drying system

A combination microwave/vacuum drying system (MIVAC) is a unique dehydration technology to produce puffed dried fruit products. The heating mechanism of the microwave process differs from conventional dehydration processes. Therefore, temperature measurement and control are critical product quality in the MIVAC process. The objectives of this thesis were to determine the appropriateness of temperature measurement and evaluate temperature rise characteristics in relation to the power levels, and the dielectric properties of grape as a function of moisture content and temperature. Thompson seedless grapes and water were treated in a batch type of the MIVAC system. The results of water experiments indicated the infrared temperature detector had certain lower power level such as 500 W had faster temperature rising curve than the other power levels. The grape experiments indicated moisture content is a major factor that affected the dielectric constant of grapes.