Originally Posted by clengman
Grapes have a lot of sugar, enough that you really don't need to add any sugar to make a wine. Most other fruit doesn't contain nearly as much natural sugar so if you want a final product with 7 or 8 % or more ABV you need to add sugar. You can start out with juice and measure the specific gravity. If it's under 1.065 or so you'll probably want to add more sugar. Or if you want to make, for instance, a berry wine, you can use grape juice or apple juice concentrate in place of sugar to boost the initial gravity, but really the end result is the same for the most part.
Well, some grapes don't have much sugar at all, unless you're talking about wine grapes. Native grapes may only have a touch of natural sugar.
That's why sugar is added, to boost the alcohol content of non-sweet fruits.
Apple juice might be the best wine to start with, if you don't want to add any sugar. Apple juice might be at 1.050-1.060 or so. Other fruits commonly available to us do not have enough natural sugar, aside from wine grapes.