Microwave-assisted freeze drying: The role of power input and temperature control on energy efficiency and uniformity

Abstract

Microwave-assisted freeze drying is fast and energy-efficient but can suffer from uneven microwave field distribution, leading to over- or under-processing in various product regions. This limits its time- and energy-saving potential, as concerns over product damage and uneven drying remain. Little is known, however, about the extent and how to address process inhomogeneity directly within the microwave-assisted freeze drying process. This study tackles these issues by analysing how power input and temperature control impact drying time, energy use, and temperature uniformity.

We compared microwave power settings ranging from 120 to 220 W (1.00–1.83 W/g) without temperature control to a temperature-controlled process that limits the drying temperature to 40 °C by reducing power near the end of drying. Results showed that higher power reduced drying time and energy use but increased temperature inhomogeneity. However, temperature control—especially at higher power levels—reduced temperature inhomogeneity with minimal negative effect on drying speed. By combining high microwave power with temperature control, the process achieved both, efficiency and uniformity. High power at the beginning accelerated drying and lowered energy use, while power reduction at later stages minimized temperature inhomogeneity at its peak. This study shows that targeted process control can successfully balance speed, energy efficiency, and temperature uniformity.

Our findings highlight the potential for simple control measures to address key challenges in microwave-assisted freeze drying, supporting more sustainable and gentle drying methods for future applications.