Cranberries on their own are quite tart, similar to limes. When you buy Cranberry Juice that says it is 100% juice, it is typically combined with the juice of other fruit such as apple, grape of cherry. However, if you purchase cranberry juice that does not claim it's 100% juice, it is likely combined with corn syrup to make it sweet. This is usually called Cranberry Cocktail. I recommend using either 100% cranberry juice, although it is most likely combined with other juices, but the sugars are natural, whereas the sugars in cranberry cocktail are not.