Involved in the production of dextran, an extracellular glucan polymer. [(1->6)-alpha-D-glucosyl](n) + sucrose = [(1->6)-alpha-D-glucosyl](n+1) + D-fructose Optimum pH is 5.0. Optimum temperature is 35 degrees Celsius. Synthesizes water-soluble glucans (alpha 1,6-glucose). Belongs to the glycosyl hydrolase 70 family.