Since Elderberrys have a high Acidic content, I use between 5 and 6 cups of berrys per gallon of wine. Any more than that and I believe the yeast will have a problem producing alcohol. Yeast can not survive in high acid enviorments.
This year, as I was making Elderberry Jelly, I got to 7 batches of jelly and still had a little over a pint of pure elderberry juice left over from the jelly making so I decided to dilute that juice in a pot and see if it works out. It may be a little more acidic than my normal batches, but the yeast did its job just like any other gallon batch of wine. From past mistakes I know too many Elderberrys can ruin the batch because of the acid content, hence the 5 to 6 cups per gallon measurement. All I did was dilute the juice with the same amount of water as a regular batch and bring it to a rolling boil for about 3 minutes to pasteurize it.
A pint of pure juice per gallon has just about the same color in the jug as the others have. I figure that 6 cups of berrys probably don't have that much pure juice in them. When I taste it I'll know for sure.
This will help me out since I have about 4 qts of Edlerberry juice frozen and I may not have to make just jelly with it.