here at mother Earth News. I did it last year with my blackberries, and will be making a lot more this year. I started with blueberries this year. The juice concentrate can be turned into a drink any strength you like, from a really sweet juice to something more like fruit water.
It's super easy too!
1. Thoroughly rinse berries, and place them in a heavy pot with just enough water to make them bob. (I used 3 pounds of blueberries and 4 cups of water) Bring to a slow boil, mash with a potato masher or spoon, bring back to a boil, and remove from the heat. Cool slightly.
3. Return juice to the pot and sweeten to taste with sugar, honey, or other fruit juices (such as pineapple). I warmed the juice back up a bit to help the sugar melt. Under-sweeten, because you can always add more sugar later, but you can't restore lost tartness. (I used about 1/2 cup of raw sugar) At this point you have a concentrate, which can be diluted with 3 to 4 parts water.
4. Pour it into clean hot jars, leaving half an inch headspace and seal. Or freeze your concentrate in ice cube trays or small freezer containers.