Ground beef should not be left out of the fridge at room temperature for more than two hours. This two-hour rule applies to all perishable foods, not just ground beef. The reason for this is related to food safety and the risk of bacterial growth.
Bacteria thrive in temperatures between 40°F (4°C) and 140°F (60°C), a range commonly known as the "danger zone." When ground beef is left at room temperature, it can quickly enter this danger zone, promoting the rapid growth of harmful bacteria, such as E. coli, salmonella, and others, which can cause foodborne illnesses.
Refrigeration slows down the growth of bacteria, which is why perishable foods like ground beef should be stored in the refrigerator or freezer to keep them safe to eat. If ground beef has been left out for more than two hours, it is best to discard it to avoid the risk of food poisoning. If the ambient temperature is particularly warm (above 90°F or 32°C), the time that ground beef can safely stay out of the fridge is even shorter, reduced to just one hour.