We’ve been dehydrating Walla Walla Sweets like mad this year, keeping the dehydrator going ’round the clock. This is actually the first time we’ve used our dehydrator, so we spent some time looking for information about drying onions with a high water content like Walla Walla Sweets and didn’t find much. While this information is fairly simple, it doesn’t appear to be out there anywhere else. Please let us know if you find this helpful.
Most instructions we were able to find for dehydrating onions said they should take about 12 hours. Given the higher water content of Walla Walla Sweets, we’ve found them to take a fair while longer. At 125 degrees, it’s been taking our dehydrator about 32 to 48 hours to finish the job, depending on how thick we layer them on.
To prepare the onions, we just ran them through our food processor with the slicing blade. This produced a nice thin slice which increases the surface area to volume ratio, which should reduce drying time. Before loading into the dehydrator, we let the onions sit for a little while in a mixing bowl in the fridge to rest. Pulling them out of the fridge, we were able to drain off some moisture before loading them up, which should further cut drying time a bit.
Make sure to dehydrate your onions outdoors, because it creates a strong odor for quite some distance. I would really hate to think how strong the smell would have been if we had done it indoors.
Store the dehydrated onions in an airtight container in a cool, dark place. We vacuum seal ours in jars. You can crush them up as you put them into the jars, which will make it easier to get them out of the jars later. Use the onions in soups or sauces. Make sure there is enough moisture to reconstitute them, and that you add them early enough that they have time to soak up the moisture. You may also be able to reconstitute them in hot water before adding them to a dish.
Good luck, and if anyone else has any better information or alternate techniques, please comment.