"Ionic wind" tech could revolutionize the fruit-drying industry

"Ionic wind" tech could revolu...
Orange slices that were quickly and efficiently dried using the new technique
Orange slices that were quickly and efficiently dried using the new technique
View 2 Images
Orange slices that were quickly and efficiently dried using the new technique
Orange slices that were quickly and efficiently dried using the new technique
A diagram of the ionic wind fruit-drying system
A diagram of the ionic wind fruit-drying system

When you think of processes that could benefit from a high-tech makeover, the drying of fruit may not be the first one that comes to mind. It turns out, however, that the use of "ionic wind" for fruit-dehydration both saves energy and preserves nutrients.

For most of us, the application of heat may seem like the obvious choice for the drying of fruit. Unfortunately, though, subjecting fruit to high temperatures reduces its flavor and destroys much of its nutrient content.

Instead, commercial food producers typically utilize a "non-thermal drying" process, in which fans blow unheated air across the fruit to gradually evaporate the moisture out of it. This technique does leave most of the flavor and nutrients intact, but it also takes a long time and uses a lot of electricity.

Seeking an alternative to the power-hungry fans, scientists at Switzerland's Empa research institute looked to a phenomenon known as ionic wind. To understand how it works, you first have to consider that air is composed of gases such as oxygen, carbon dioxide and nitrogen. The atoms that make up each of the gas molecules in turn consist of negatively charged electrons and heavier positively charged protons.

When a suspended wire is positively charged to a high voltage, the electrons are thus drawn towards it, while the protons are repelled. In fact, the electrons actually split off from the nearby gas molecules, leaving the protons behind.

As a result, the gas molecules are now only positively charged, so they move away from the wire, towards a grounded collector located beneath it. While on their way to that collector, they collide with neutrally charged gas molecules, sending them heading in the same direction. All of those moving molecules ultimately create a wind.

In previous studies, scientists only had limited success using ionic wind technology to dry fruit. This time around, however, colleagues at Canada's Dalhousie University took the extra step of placing the fruit on a grounded mesh instead of an impermeable tray. This made a huge difference, as moisture could now evaporate from all sides of the fruit, allowing it to dry twice as fast and in a more uniform fashion.

"Now this isn't exactly rocket science, but so far no one has considered this adaptation for the drying with ionic wind," says the study leader, Prof. Thijs Defraeye.

When compared to conventional non-thermal drying techniques, the mesh-augmented ionic wind method was found to be much quicker, plus it dried the fruit more evenly while preserving more nutrients, and it consumed less than half as much energy. According to the researchers, it should also be fairly easy to scale the system up for industrial use – Empa is now working with a Swiss retailer on commercializing the technology.

Source: Empa

The ionized air might also reduce microbial growth. If people with mold sensitivities have problems with dried fruit, this new technique might solve that.
This article caught my eye because I just finished making a simple food dehydrator of my own a couple of weeks ago. It uses two fans (one blows in, the other out) from old computer cases and four incandescent light bulbs. With the lights on it reaches a temperature of 53 degrees Celsius, with the fans 31 degrees is maintained. It consumes 300 watts and takes 2 days to dry 2 dozen apples. I have also done chili peppers, parsley, and pears with excellent results. I hope this ionization process is efficient and economically effective and not some kind of rube goldberg solution because dried food requires no refrigeration, its nutrients intact and quite tasty. The dried parsley turns a bright green in a dish, just like as if it was fresh. I am quite pleased with the results.
I wonder how this process compares to room temp vacuum drying.
Also instead of grounding the mesh, it could be used as the cathode to charge the water in the fruit, which could be drawn to an anode collector above or below.
Bruce H. Anderson
How does this compares on energy usage to freeze-drying?