Temperature and power control in microwave drying

A microwave drying system with the ability of automatic temperature and power control was developed for apple drying. The samples’ mass and the moisture content could be obtained online. Four different drying modes were attempted with different combination of temperature and power controls. Feedback temperature control with predefined variable power profiles resulted in the best temperature control and product quality. All other modes proved their own pros and cons. The study also verified that it was difficult to maintain a constant temperature during microwave drying process when a feedback temperature control was not included. The results can be used to determine microwave power levels in microwave drying practices both with and without temperature control.