Application of Microwave Drying Technology in the Food Industry
Food typically has a moisture content of 30% to 97%, and the use of microwave drying or microwave enhanced drying of food has broad application prospects.
(1) The microwave quick drying of food, such as using microwave heating to dry vegetables into "dry vegetables" with a moisture content of less than 20%, can be more than ten times more efficient than traditional methods. This method is not only suitable for drying vegetables, but also for drying seaweed based foods. Observing vegetables that have been microwave dried under a microscope, it can be observed that their tissues are second only to freeze-dried products in terms of similarity to fresh vegetables, but their drying time is shorter than freeze-drying. Microwaves can also be used for final drying of fried products, which not only saves fuel but also produces light and delicious food with low oil content.
Drying dough with hot air takes 5-8 hours to avoid crust or cracking, while microwave drying only takes 1-2 hours to dry from the initial moisture content to 20% and use hot air to remove moisture, saving 25% energy. Microwave drying can also reduce bacterial contamination, such as combining hot air and microwave drying of garlic. Hot air dries the moisture from 80% to 10% (wet basis), and then microwave drying is used to 5%, reducing the total number of bacteria by 90% and saving energy by 30%.
Microwaves can process materials that deteriorate or degrade at temperatures above 40 ℃ (sometimes even 15 ℃) in a vacuum state. Vacuum drying ovens can only conduct heat and usually do not have convective heating, resulting in long drying times. Microwave vacuum drying products include concentrated 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 substance, which is laid on a conveyor belt and passed through a specially manufactured tunnel (vacuum degree of 133.3~2666Pa) to form a foam with good rehydration performance.
