How to make a microwave vacuum dryer with turntable

Abstract

A domestic microwave oven was modified in order to operate as a microwave vacuum dryer with turntable. The dryer performance was assessed with banana, grape tomato and carrot slices, dried under vacuum. Three different levels of microwave power (400, 700 and 1000 W) were tested to evaluate the influence of microwave power on the drying. The experimental results showed that it is possible to produce dried fruits and vegetables with characteristics similar (crisp and crunch) to those produced from a freeze-drying process, in much shorter process times, e.g. 20 min against the 14–16 h, typical of freeze-drying processes. The system presented in this work is a low cost, flexible and ease-to-assemble device, which can be made from domestic microwaves. It works properly with turntable, under vacuum that allows controlling the temperature and leads to uniform food heating, which improves the quality of the dried fruits and vegetables. In this way, this low-cost microwave vacuum drying is very useful to investigate the drying of fruits and vegetables at lab scale, and can be the base for making larger equipment.