In the title mol-ecule, C(17)H(20)O(8), the two pyran rings form a dihedral angle of 61.2 (2)°. The two hy-droxy-methyl groups are each disordered over two sets of sites in a 0.764 (3):0.236 (3) ratio. In the crystal, O-H⋯O hydrogen bonds link the mol-ecules into layers parallel to the ac plane.