Once you think things are dry enough, fill the jar only about 2/3 of the way, lid it, then let it sit for several days where you can easily see it. Every day, shake the jar gently and turn it all around. You’re looking to see if anything sticks to the sides or bottom and can’t be easily dislodged, or if there’s clumps that don’t fall apart. Both of those things indicate that it’s not completely dry; take the food out and dry it longer right away. This process is called conditioning and it makes it easier to catch incompletely-dried foods before they go bad.
Caveats:
1. High-sugar foods (fruit, including tomatoes) can be a sit stickier even when completely dry. Even so, they should be relatively easy to dislodge with a shake. If you have to get your hand or a utensil in the jar to loosen them, dry more.
2. Powdered food takes a bit of additional handling. (I love doing powdered mixed green stuff to add to just about anything we eat.) For that, dry your food in reasonably-sized bits, powder them in a mortar and pestle, then lay them out on drying racks again in a warm location, such as near your wood stove. (I use parchment paper to keep the powder from falling through the holes in the racks.) Stir the powder once or twice while it’s drying. Then do the same conditioning process as above.
3. Tomato powder, being both fruit and a powder, will stick no matter how careful you are. Just dry those tomatoes until they snap or shatter when you try to break them and give them an extra-long second drying once they’re powdered. Even then, I often have to chisel the product out of the jar, but it’s so useful and space-conserving that I do it anyway!