Can you use frozen blueberries instead of fresh berries?
Yes, you can. This soda recipe is written for fresh blueberries, however it can also be made with frozen berries. When using frozen blueberries, thaw them first. Start by making the sugar syrup (ie. dissolve sugar in water over low heat) as usual and then add in the thawed fruits. Cook the fruits for a few minutes until they turn completely soft.