When dehydrating tomatoes it is best to use a meaty style tomato. I use Roma tomatoes both for canning and dehydrating. Choose firm ripe fruit. You don't want the tomatoes to be over ripe
Wash and slice. This little vintage slicer works really well for slicing tomatoes. It makes the slices even and will do a whole tomato.
The more evenly you make your slices the more evenly it will dehydrate. If you don't have a slicer like this, simply use a very sharp knife and make your slices as even as possible.
Lay the slices out on a dehydrator tray. Be sure air can flow freely between pieces.
Dehydrate at 145 degrees until crispy. 6 to 12 hours. This is a wide range, actual time will vary with the juiciness (is that a word?) of the tomato and your dehydrator. Check your trays every couple of hours and rotate if it seems one area is drying much faster.
Store in an airtight container. I usually use a recycled mayonnaise or similar type jar or a regular canning jar. Re-hydrate or add to soups and stews. They can even be snacked on just like they are.
Dehydrated tomatoes can be ground in a blender and made into tomato powder. This can then be re-hydrated and made into tomato paste or sauce. Or use it to thicken up tomato based soups or stew. It will add a lively tomato flavor.
Just place dried tomatoes in a blender and blend until it is a powder. You may have to stop occasionally and scrape the sides but I've not had a problem with getting it all blended.
For storage place it in an airtight jar. Turn the jar upside down and leave it on the counter for a day or two. Watch for any moisture in the jar. If you notice moisture, your tomatoes were not dry enough. Store this in the freezer. If no moisture shows up, it is good to go on the shelf.
I did this with some yellow pear tomatoes as well as the roma tomatoes. I have yet to use it but I expect it to be good!
To make tomato paste, mix water and powder in a ratio of 2:1.
For a tomato sauce mix in a ratio of 4:1 Add seasonings if you like.
Or simply add to soups stews etc as a thickener.
Use tomato powder to make a tomato sauce and then add garlic and seasonings to make a pizza sauce.