Freeze dried blueberries are blueberries that have had all the moisture removed from them. The blueberries undergo a process whereby they are frozen and placed in a vacuum. This causes the moisture in the berries to turn from ice to gas, and it is completely extracted from the blueberries. What you are left with is a crispy blueberry that still has all its flavor but no moisture whatsoever. Unlike dried fruit which can be chewy and sticky, freeze dried fruit is crisp and crumbly. This complete lack of moisture makes freeze dried fruit a great option for flavorings in macarons, cake batter and buttercream, as you can add concentrated flavor without adding moisture.