According to the USDA safest way to defrost frozen minced beef is in the refrigerator. This is so because the meat is kept at an ideal temperature the whole time. The ground meat should then be used within 24-48 hours of thawing. One can also defrost the meat by placing the meat in a waterproof bag and submerging it in cold water. Change the water every 30 minutes and cook as soon as it is thawed.