The present invention relates to the use of carbon monoxide as a process aid to enhance the re-bloom of ground beef after packaging in a chub. In the present invention the ground beef is exposed to a treatment gas containing carbon monoxide before being packaged in the chub. The carbon monoxide converts some amount of the myoglobin in the ground beef into carboxymyoglobin, which has a desirable bright-red color. The carboxymyoglobin is not transformed to deoxymyoglobin while in the chub by the enzymes present in the meat. Therefore, when the chub is opened by a consumer or intermediate retailer the presence of the carboxymyoglobin enhances the re-bloom.