Starbucks' frappuccino has a fairly smooth consistency and mouth-feel. When I attempt to make something similar with my stick blender, I tend to end up with a layer of ice crystals floating on the top of the drink, which spoils the texture.
I've found that adding a banana seems to prevent this from happening. Is there some chemical reason for this? Does the Starbucks frappuccino mix have some additive for this purpose?