Production of extracellular glucans, that are thought to play a key role in the development of the dental plaque because of their ability to adhere to smooth surfaces and mediate the aggregation of bacterial cells and food debris. [(1->6)-alpha-D-glucosyl](n) + sucrose = [(1->6)-alpha-D-glucosyl](n+1) + D-fructose Glucan synthesis by GTF-S is independent of primer glucan unlike GTF-I. Synthesizes water-soluble glucans (alpha 1,6-glucose). Belongs to the glycosyl hydrolase 70 family.