Microwave/Dielectric Driers – Continuous, Solid, Not Heat Sensitive
Industry: Fruit and Vegetable Preserving and Specialty Food Mfg (NAICS 3114)
Process Brief: Moisture in pasta, fruits, and vegetables is removed using electromagnetic radiation.
Energy source: Electricity Energy Intensity: 1,500 Btu/lb of water in the product
Dielectric driers use microwaves or radio frequencies to dry food by using electricity to heat the water in the product. Most other food drying technologies use hot air or hot surfaces to transfer thermal energy to the product. Microwave driers use a magnetron to generate electromagnetic radiation that causes the water molecules to vibrate and generate heat. Dielectric driers have two metal plates and the product is placed between the plates. The plates are energized with opposing polarity that is rapidly reversed causing the water molecules to vibrate and come to the surface of the product. Dielectric driers require good contact between the plates and the product, which can be difficult. Both types of driers are efficient and rapid but can heat unevenly resulting in quality problems for some products.
Microwave and dielectric driers have found their greatest use in the drying of pasta but both types of driers have found limited applications elsewhere in the food industry. Two obstacles to greater use are the inability of microwaves to penetrate thicker products and the difficulty of matching dielectric plates to specific product shapes. Generally, microwave and dielectric driers are effective in bringing water to the surface of the product and are used in combination with forced air driers that actually remove the moisture from the product. Continuous microwave driers use a conveyor to move the product through a shielded microwaving zone. Continuous dielectric driers use groups of plates and a mechanized handling system that essentially automates the material handling to achieve continuous production.