Confidence votes 4.8K. It doesn't. A raisin has as much sugar as a grape, assuming the producer didn't add corn syrup or sugar to the raisins. Because, however, raisins have had most of the water removed, the amount of sugar per ounce is going to be much more for raisins than fresh fruit. An ounce of raisins might contain several dozen raisins (which have the sugar of several dozen grapes) versus an ounce of grapes, which contains, perhaps, 8 grapes (the sugar content of 8 raisins).