How do you make dried blueberries? Can I use an oven? Is there a proper technique or do I just bake them on low for a few hours?
While you could probably do dried blueberries in a VERY low oven (150F), you'll most likely need to prop the door open slightly to allow moisture to escape. You'd be best to do them in an actual food dehydrator which will have a fan to expell the moisture being released from the food.
Keep in mind however that if dried as they are, they will shrivel up into fairly hard little bits. If your goal is something similar to the dried blueberries that you can buy in retail stores, they will have to be treated in a sugar syrup to maintain the chewy texture and keep them from totally drying out. I'm not sure if the commercial producers are first drying and then soaking in a sugar solution and perhaps drying again so that the sugar is drawn into the cells of the berry. Whatever the case...commercial dried cranberries and blueberries maintain the chewy texture due to being treated with a sugar solution at some point.
If you are looking for ways to handle a bumper crop or bulk buy on blueberries, I would recommend freezing them and stick to buying commercially processed dried berries for the best results, least effort, and greatest bang for your buck.
I have made dried blueberries in the oven by simply placing them on a baking sheet and drying for about 12 hours at the lowest temperature my oven would go (250). 12 hours at 250 was way too long. While the berries are edible and a similar texture to what you would get if you put them in a dehydrator, they taste a bit burnt. If you can find the magic temperature and time combo, I like the taste of bluberries dried in a dehydrator or done correctly in an oven quite a bit.
After that experiment, I've decided to stick to making fruit leather. I use the basic guidelines from Simply Recipes and actually dry the leather in the back of my car on a hot day. It tastes great!