Beta-glycosidase that catalyzes the transfer of glucose moiety to anthocyanidin 3-glucoside at the 7 position. Anthocyanins are ubiquitous colored pigments that are responsible for variations in petal color. 1-O-(4-hydroxy-3-methoxybenzoyl)-beta-D-glucose + cyanidin 3-O-beta-D-glucoside = cyanidin 3,7-di-O-beta-D-glucoside + vanillate kcat is 0.17 sec(-1) with cyanidin 3-glucopyranoside (at pH 5.0 and 30 degrees Celsius). kcat is 0.10 sec(-1) with 1-O-beta-D-vanillyl-glucose (at pH 5.0 and 30 degrees Celsius). Optimum pH is 6.0. Optimum temperature is 40 degrees Celsius. Pigment biosynthesis; anthocyanin biosynthesis. Belongs to the glycosyl hydrolase 1 family.