For maximum sweetness, the berries should be picked not when they are a shiny black color, but when this color has dulled and they come off the plant very easily. If you have been picking them when they are a shiny black color, then they will have a tart taste.

Sugarshane:

Second the motion on what Austransplant said about the duller color, and would add only that ripe blackberries tend to separate from the plant with a very tender pull. Trouble is, at that stage they are also about ready to fall off, and if that happens they are usually ruined. They do not accumulate more sugars once they are off the canes.

But let's be realistic. Blackberries are not intrinsically a very sweet berry until they reach the danger point for falling off, and when picked at the dull stage their shelf life is very short indeed. You either have to eat them, process them, or freeze them very quickly. For industrial uses like jellymaking, winemaking, or cobblers, where some sugar is added, I wouldn't wait until the very end.

Don Yellman, Great Falls, VA

thanks for the responces. seems i'm picking too early,when there shiny black. they are great in the last 4 pies i've made,also made 2 batches of jelly, but haven't tasted it yet and i don't even think even half the berries are ripe yet. unbelievable producer of huge berries.
thanks.......Jim

Thanks1 Was going to ask this Q myself.

Eating at vine swell druplets are dull black has highest sugar content. Then when we want pie cobbler blackberry dumplings cobbler blackberry homemade icecream are jelly we pick blacks so these food have tart taste. At harvesting you can get tartness to increase by adding few (12) with red druplets 3 to 5 per berry in gallon berries. sugarshane you put berries in gallon ziplock press to seal type bag in freezer do jelly later in winter when need heat up house.