Dielectric Properties and Microwave Processing

In the food industry, microwave heating has applications primarily in thawing, cooking, drying and pasteurization. The number of installations is slowly growing. In addition to economical feasibility, successful applications must meet technological requirements such as good energy utilization and control of the temperature development in the foods — the uniformity of heating. Both oven design factors and the food composition and geometry influence the uniformity. The dielectric properties of foods are important for the interpretation of the influence of the electromagnetic wave nature of the microwave on the temperature distribution in the food material. Available data and prediction models for dielectric properties is reviewed and the major dielectric measuring methods commented on. Different methods for distributing and controlling the microwave field in microwave oven are described. Microwave penetration is influenced by food composition and the microwave field of the heating system in the oven. Food geometry greatly influence overheating phenomena such as centre overheating of round foods and corners and edges of brick shaped foods. Some future perspectives and questions are finally given.

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