Freshly juice the grape juice - I used about 1/2 large bunch of black grapes, but you can use whatever type of grape you like most, or, as said, buy a good organic grape juice.
Muddle the blackberries, mint and lemon juice until mostly pulverized.
Add blackberry mix, along with vodka and grape juice, to shaker with ice and shake it up!
Pour into cocktail glass and float seltzer on top if using, and add additional sprig of mint.
Cool off all summer long. You can up the recipe and make a pitcher of these beauties for any garden gathering as well. Its very easy to drink, so mind your refills;)
