A gallon of "sugar wine

How much sugar would one use to make a gallon (3.8 litres) of water with a S.G. of about 1.090 (P.A. of about 12%)?

Yesterday someone gave me about 7 pounds of some tiny pruple grapes. (They're about the size of smallish blueberries. If anyone has a guess as to what they are, I'd be interested. They were grown here on the west coast, near Vancouver BC.) I squeezed them and got a little more than half a gallon of juice, and added about 3 cups of sugar, and water. (I'm not planning to ferment on the skins. The must is quite red.) The S.G. is about 1.100. The must is obviously sweet, but there's something not right about it ... I'm not sure if it's sour or bitter. It sort of sets the teeth on edge.

So my plan is to lessen the influence of this not-great grape flavour on the wine by diluting it into 2 gallons. Three-and-a-half pounds of fruit per gallon seems to me acceptable for a country wine. So how much sugar would I use to make a gallon of "sugar wine"? Or, if anyone thinks this is a bad idea, I'd be happy to hear of alternative suggestions.

Thanks,

Jeff Hay-Roe Sechelt, B.C.