It takes about 20-30 minutes to cook a typical store-bought bratwurst (like Johnsons) at 350°F. Flip the bratwurst as needed to ensure even browning. To check whether the bratwurst is done, insert a food thermometer into the center of the bratwurst. If the temperature is 160°F, the bratwurst is safely cooked per the United Stated Department of Agriculture (USDA).