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Sear the rib roast (prime rib) for 15 minutes at the higher oven temperature (450 degrees F.), then turn the oven to the lower temperature (325 degrees F.) for the rest of the cooking time. Every 1/2 hour, baste the cut ends of the roast with the fat accumulated in the roasting pan. Do Not Cover the roast.rime Rib Roast (standing rib roast), at room temperature (very important) 2 tablespoons butter, room temperature. Preparation: Preheat oven to 450 degrees F. Pat the room-temperature standing rib roast (prime rib roast) dry with paper towels or napkins.
According to the Wyoming Beef Council, a prime rib roast will be medium rare when it reaches an internal temperature of 135 degrees F and medium when it reaches 150 degrees F.They say to remove the roast from the oven 5 to 10 degrees before it reaches the desired temperature.our most important tool for knowing when your prime rib is done to perfection is with a good quality meat thermometer. The time to start monitoring the internal temperature of your prime rib is at least 45 minutes before you expect it to be done.