I sweeten mine to a hydrometer reading of somewhere between 1008 to
1012. However you may prefer yours a little more or little less
sweet....It may be best to sweeten to 1005, then sample, and go from
there, adding more sugar to taste. I have tested the commercial
blackberry wine in my area and found it has a reading of 1025, but
that's far too sweet for my taste buds....And don't forget to add
sulphite and stabilizer.
I like blackberry wine between 1.008 and 1.012.
There are several ways to achieve this sweetness, but the two most
popular are to either add sugar dissolved in water, fresh juice or wine
or to add honey.