Electromagnetic monitoring of the drying of in-shell Macadamia nuts

Macadamia nuts require drying to facilitate shelling, to improve the taste, and to extend shelf-life. In this research, the dielectric properties of whole nuts (kernel in shell) were measured using a coaxial resonator and an inexpensive vector network analyser, during the course of drying procedures. It was found that a collection of raw nuts had a real relative permittivity of 1.4 at low frequencies, which increased to 2.1 at 0.24 GHz, and an imaginary relative permittivity of 0.015 at low frequencies, rising to 0.10 at 0.24 GHz. With increased drying, both components decreased. The relative permittivity correlated with mass loss during drying. It is expected that the results can be used in designing a real-time drying monitor, and a radio frequency or microwave heating scheme for drying.