If fruit or vegetables are dried using heat, nutrients can be destroyed and flavorings lost. This is why non-thermal drying of food is particularly popular in the industry. A new drying process developed at Empa using ionic wind now promises more energy-efficient, faster and even gentler drying of food compared to conventional methods (e.g. using fans).
An ionic wind is created by connecting a metal wire to a positive high-voltage source of typically 10,000 to 30,000 volts. This charges the wire positively and ionizes the surrounding air. The electrons are attracted to the positively charged wire, while the much heavier protons are repelled from the wire. On their way from the wire to the earthed collector below, the positive ions collide with other air molecules and push them against each other. This impulse and the resulting particle movement create the ion wind, also known as the electrohydrodynamic air current.
Researchers have tried to use this ionic wind for the industrial drying of food, but so far without any notable success. However, the Empa researchers did not place the food to be dried on a plate as before, but used a grid, a simple method that apparently no one had tried before. This allows the water to escape from all sides of the vegetables and fruit, and the food dries twice as fast and more uniformly than on an impermeable surface due to the ionic wind. In contrast to the previously used approaches of electrohydrodynamic drying, the new design can also be scaled up more easily and is therefore also extremely interesting for industry.
