Making homemade raisins takes a lot of work and takes a full two days of running the dehydrator on medium-high heat, but the raisins are so flavorful and different than what you buy at the store!
For these raisins, I had two paper grocery sacks of purple seedless concord grapes, a full stack of 10 dehydrator trays, and that equated to about a quart jar and a half of dried raisins.
First, you want to choose some home-grown, seedless table grapes (much more flavor than your standard grocery store grapes). You’ll only be able to get these in the late summer or early fall here in the temperate zone of the northern hemisphere, but when you do get them, you’ll probably be able to get your hands on a lot, and all at once. Be sure that you have lots of trays for your forced air dehydrator!
Remember what I said about it being a lot of work? Well, this is that part… Wash and de-stem your grapes, sort out the bad ones (compost or chuck them), and slightly squish each good one just until it pops open a little. (This will help speed dehydration. Cutting each grape in half, halves the time they take to dry, but it is a lot of work and makes your fingers sore, so I wouldn’t recommend it.) Place each popped grape on a dehydrator tray.
Set your dehydrator on medium high heat and begin the dehydration process. Check the grapes after a day, but I bet they will still be nowhere near done. I would let go a full two days, to be honest. Even then, depending on the size of your grapes (and whether or not you popped them), you may have to go even longer.
After your raisins are dry, try one. You will notice right away that the flavor is so much more vibrant and tart than that of a normal store-bought raisin! These literally taste like what you would imagine a dried grape should taste like, if you’d never tried a store bough raisin. And now you can see why some people live a lot of their lives not knowing that raisins are just dehydrated grapes!