For the last 14 or 15 years, in addition to canning I have dehydrated foods. No particular reason other than I could and I had a dehydrator or 2. The first was given to me, a Ronco. Then several years later I found it's twin in a thrift store, complete with everything that came with it accept the box. As far as I could tell it had never been used and for $5 I figured it'd be good for the extra trays and parts if I ever needed them.
That was the plan at the time. Then I started using BOTH of them because one just wasn't enough, I had found even more things to dry out. And over the last 2 years or so it became apparent I needed yet another one to handle my load. So for Christmas I was given an Excalibur 9 tray electric fan monster of a dehydrating machine. It was in service the very next day working on a bunch of cabbage I found on sale. It's been in steady use since. Though at the rate I'm going I may end up pulling the Roncos back out once this garden comes in just to keep up!
So what do you do when you find onions on sale or happen to have a lot come out of your garden and no root cellar or other adequate storage for them? Pass them up? Give them away? Noooooo!!! You pull that dehydrator out! You can use that dehydrated onion later on in soups, stews, casseroles, etc. You won't have to chop one up if you are in a hurry to get everything in the pot.
So how is the next big question. It's easy really. Take that outer skin off your onions, trim the top and bottom and chop it up. How big or small depends on your dehydrator. In the Excalibur I have screens that can manage 1/2" pieces without letting too many tall through once they've dried to rice grain size. In those Roncos though, I didn't chop, I sliced and separated into rings. Then everything gets dunked in water for a quick soak to help pull out some of the vapors. Usually just over night. No more than 10 hours.
Then we drain and let sit in colanders until they stop dripping. This is the 6 pounds I started with the other night:
Next we load the dehydrator trays in as single of a layer as you can manage:
For the Excalibur I just turn the dial to vegetables/125* after putting the lid in place and walk away for 18 to 24 hours depending on how much water the onions had in them. For the Ronco, I would rotate the trays every 4 hours or so until the onions were completely dry, usually about 24 hours for the rings. This is what the above loaded tray looks like when done:
Let the onions cool for about a half hour or so after they are dried out. 6 pounds of dried onions takes up a lot less space for sure, a quart jar is more than enough to hold everything without them being packed in there! I also have a vacuum sealer that has a wide mouth jar attachment so I vacuum out all the air in these jars for longer shelf life.