Maturation of a virion after separation from the host cell. Not all viruses mature after separation. In those that do, maturation typically involves rearangement and/or cleavage of viral proteins, resulting in the virion becoming competent for reinfection. [ http://viralzone.expasy.org/all_by_protein/1946.html https://www.worldcat.org/search?q=bn%3A0781718325 https://www.uniprot.org/keywords/KW-0917 ]