There are a few ways to tell if a burger is 100% cooked without cutting it open:
Touch test: One common method is using the touch test. As the burger cooks, it will become firmer. You can use your finger to gently press the center of the burger. If it feels soft and squishy, it's likely still raw in the middle. If it feels slightly springy, it's probably medium-rare to medium. When it feels firm and doesn't yield much to pressure, it's likely well-done.
Thermometer: The most accurate way to determine if a burger is fully cooked is by using a meat thermometer. Insert the thermometer into the thickest part of the burger, avoiding the bone or any pockets of fat. For beef burgers, a safe internal temperature is 160°F (71°C). For poultry or pork burgers, the safe internal temperature is 165°F (74°C).
Visual cues: As the burger cooks, its color will change. A raw or undercooked burger will be pinkish-red in the center, while a well-done burger will be uniformly brown throughout. Keep in mind that visual cues may not always be accurate, especially if the burger is made from ground poultry, which can remain pink even when fully cooked.
Time and experience: With practice, you can develop a sense of how long it takes to cook burgers to your desired doneness. Cooking times can vary depending on the thickness of the burger, the heat of the grill or pan, and the type of meat used.
Remember, it's essential to cook ground meat, especially poultry and pork, thoroughly to prevent foodborne illnesses. Using a meat thermometer is the safest way to ensure your burgers are cooked to the appropriate temperature and are safe to eat.