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I also have a UDS and I will cook the ribs in a rib rack without foil for about 5-6 hours at 225 deg F. I will spritz hourly with apple juice to help maintain moisture. I know when they are done by the meat pulling back from the bones 1 or 2 inches and the way the meat cracks when I hold it in the middle with tongs. I like this method better than the 321 method as the ribs come out a bit smokier and not quite fall of the bone but very close.