Color: Ground beef that is gone bad may have a slightly flat gray color. However, the USDA notes[1] that the interior of packaged ground beef can be gray or brown while the surface is red; this is due to lack of oxygen penetrating below the surface of the meat and is not necessarily a sign the meat has gone bad. Additionally, any ground beef that has turned green is definitely rotten. Smell: When ground beef goes bad, it will start to smell off. If it smells bad to you, then it is probably spoiled. The smell of rotten meat is distinct: a pungent or nasty smell that makes you cringe or even gag. Texture: The surface of ground beef tends to become slimy when it has gone bad. It also may feel sticky or tacky to the touch. Length of time since purchase: Typically, ground beef should last in the refrigerator about one to two days from date of purchase. Either cook it within the first couple of days, or freeze. ________________ [1]https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/meat-preparation/the-color-of-meat-and-poultry/the-color-of-meat-and-poultry/ct_index