"A Scandinavian recipe for a delicious berry drink, translated for me by a friend. Good for any kind of berry. When ready to drink, add small amount of saft to a glass of water, to taste. Add more sugar as needed; stir well."
Bring blackberries and water to a boil in a large pot until blackberries are softened, about 15 minutes. Remove from heat and mash berries using a potato masher.
Line a sieve with cheese cloth; place over a large pot. Pour mashed berries through cheese cloth-line sieve; let sit until all liquid has drained through cheese cloth, about 30 minutes. Stir 1 pound sugar per 1/2 gallon of drained blackberry juice.
Bring blackberry juice and sugar to a boil in a pot; cook until sugar is dissolved, about 5 minutes. Skim off any residue accumulated on top.
Sterilize jars and lids in boiling water for at least 5 minutes. Pack hot saft into the hot, sterilized jars, filling the jars to within 1/4 inch of the top. Run a knife or a thin spatula around the insides of the jars after they have been filled to remove any air bubbles. Wipe the rims of the jars with a moist paper towel to remove any food residue. Top with lids, and screw on rings. Store in refrigerator.