The boysenberry is a hybrid between the loganberry (Rubus loganobaccus) and various blackberries (Rubus allegheniensis or Rubus ursinus) and raspberries (Rubus idaeus or Rubus occidentalis). As such, they do not grow wild except as escapees from cultivation.
Because their parentage is mixed, boysenberries vary in sweetness and tartness. The wine-red fruit of the boysenberry is high in acid content, but not as high as the fruit of the loganberry. Their natural sugar content is less than the blackberry and their tartness is less than the raspberry. As such, I am told they make a decent, flavorful wine when sugar is added to the must. In wine, the berry flavor is more subtle than wine made from either raspberries or loganberries, but more tart than wine made from blackberries. These are just reports. I have not made this wine yet myself, but I have four pounds of frozen boysenberries and intend to start a gallon in late January.
Pick fully ripe, best quality berries. Wash thoroughly and place in nylon jelly-bag. Mash and squeeze out all juice into primary fermentation vessel. Tie jelly-bag and place in primary fermentation vessel with all ingredients except pectic enzyme and yeast. Stir well to dissolve sugar, cover well, and set aside for 12 hours. Add pectic enzyme, recover and set aside another 12 hours. Add yeast, cover, and set aside for 5 days, stirring daily. Strain juice from jelly-bag and siphon off sediments into secondary fermentation vessel of dark glass (or wrap clear glass with brown paper), adding water to bring to shoulder, and fit airlock. Place in cool (60-65 degrees F.) dark place for three weeks. Rack, allow another two months to finish, then rack again and bottle in dark glass. Allow a year to mature. [Adapted from Raymond Massaccesi's Winemaker's Recipe Handbook]
My thanks to Dick Decker for this request