While leaving your frozen ground beef out on the counter helps it thaw more quickly than transferring it to the refrigerator, leaving it out for more than two hours becomes unsafe. Instead, there are several alternate methods to use for thawing it out safely before cooking it to a temperature recommended by the U.S. Department of Agriculture.
Raw meats like ground beef can last indefinitely when they are frozen, but that doesn't mean that they're still safe after they thaw. Bacteria forms and thrives on cool-to-warm ground beef and will multiply quickly and undetected. While cooking the meat thoroughly destroys most bacteria, you should not take any chances. Don't thaw your ground beef in a manner that encourages bacterial growth. The USDA advises against leaving frozen ground beef out for more than two hours, after which the risk of bacteria growing and multiplying increases.
The Best Defrosting Method
The safest way to thaw ground beef, especially if you plan on doing it gradually, is to simply transfer it to the refrigerator. This keeps it at a safe temperature -- below 40 degrees Fahrenheit -- while it thaws. Place a plate under your meat while it thaws to prevent water and juices from leaking throughout your refrigerator, and plan on giving it at least a day to fully defrost. Once your ground beef has thawed, even though it's in the refrigerator, it should be used within two days, as ground beef that has been frozen deteriorates at an accelerated rate.
If you need your ground beef to be ready to cook sooner, there are two safe methods for thawing it. The first is to use the defrosting feature on your microwave. You should only use this method if you are using the meat immediately afterward, as the microwave may start to cook the outside of it as it thaws. The second method is to seal your meat in a watertight bag and treat it with water. You may either submerge it in a bowl of cold water that you dump and refill every 30 minutes, or simply run it under slightly warm water, turning it periodically for even thawing. You should never leave your ground beef in standing warm water, however, as this encourages bacterial growth.
The only way to be completely sure your ground beef is bacteria-free is to take its temperature. Because bacteria can grow on your raw meat even when you use a relatively safe thawing method, the USDA recommends cooking your ground beef until it reaches a safe internal temperature, which indicates that lingering bacteria has been destroyed. The minimum internal temperature for your ground beef is 160 F -- check it by inserting a meat thermometer into its center.