2. Cook the ribs slowly for 1-1/2 to 2 hours, over medium heat (325° to 350°) and over a drip pan half filled with water. Long, slow cooking makes for moist and tender ribs with a crisp crust. If in the first 30 minutes the ribs are browning too quickly, shut the grill vents. 3. Determining when pork ribs are done is a little tricky, but after 1-1/2 to 2 hours, you can be virtually certain that the ribs are fully cooked. However, the meat’s color is not an indication of doneness.