The kinetics of microemulsion formation in a multicomponent blend of two homopolymers and a block copolymer was studied by neutron scattering. The scattering profiles indicate the presence of large length-scale defects that coexist with the periodic microemulsion. With time, the large-scale structures undergo coarsening, while the periodic structures undergo refinement, i.e., they become more organized. The defect density at a given temperature can be controlled to some extent by thermal history.