Foods usually have a moisture content of 30% to 97%. The use of microwave drying or microwave-enhanced dry food has broad application prospects.
(1) Microwave quick-drying of foods, such as drying vegetables with microwave heating method to "dry vegetables" with a moisture content of less than 20%, which is more than ten times more efficient than traditional methods. This method is not only suitable for the drying of vegetables, but also suitable for the drying of seaweed foods. Microwave-dried vegetables were observed under a microscope, and the tissue was found to be inferior to fresh vegetables by freeze-dried products, but the drying time was shorter than freeze-drying. Microwaves can also be used for final drying of fried products, which not only saves oil, but also provides light, delicious foods with low oil content.
Dry the dough with hot air for 5~8h to avoid crust or cracking. Dry the microwave for only 1~2h, dry from the initial moisture content to 20%, and take away the moisture with hot air to save 25%. Drying with microwaves can also reduce bacterial contamination, such as hot air and microwave combined drying of garlic, hot air drying from 80% to 10% (wet basis), then drying to 5% with microwaves, the total number of bacteria is reduced by 90%, energy saving 30 %.
Under vacuum, microwaves can handle materials that deteriorate or degrade at temperatures above 40 ° C (sometimes even at 15 ° C). Vacuum ovens can only pass heat conduction, usually without convection heating, and have a long drying time. Microwave vacuum drying products include fruit juice, tea powder, enzymes, vegetables (mushrooms, garlic, soybeans, etc.), and the operating cost is between spray and freeze-drying. In these systems, the material is usually a paste-like material placed on a conveyor belt and passed through a specially manufactured tunnel (vacuum degree 133.3 to 2666 Pa) to form a bubble with good rehydration performance.